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==CHAPTER XVIII CRUSTACEA==
History of the larval forms 1 '.
THE larval forms of the Crustacea appear to have more faithfully preserved their primitive characters than those of almost
any other group.
BRANCHIOPODA.
The Branchiopoda, comprising under that term the Phyllopoda and Cladocera, contain the Crustacea with the maximum
number of segments and the least differentiation of the separate
appendages. This and other considerations render it probable
that they are to be regarded as the most central group of the
Crustaceans, and as in many respects least modified from the
ancestral type from which all the groups have originated.
1 The following is the classification of the Crustacea employed in the present  chapter.
i Phyllopoda. ( Natantia.
I. Branchiopoda. ciadocenu III. Copepoda. Euc P e P da Iparasita.
( Branchiura
T Nebaliadse. jThoracica.
M f Sat- < v - wdi, p a minai ia
II. Malacostraca. ] Stomatopoda . ULocephaia.
I Cumacese. v. Ostracoda.
I Edriophthalmata.
2 The importance of the larval history of the Crustacea, coupled with our comparative ignorance of the formation of the layers, has rendered it necessary for me to
diverge somewhat from the general plan of the work, and to defer the account of the
formation of the layers till after that of the larval forms.
The free larval stages when such exist commence with a
larval form known as the Nauplius.
The term Nauplius was applied by O. F. Muller to certain
larval forms of the Copepoda (fig. 229) in the belief that they
were adult.
FlG. 208. TWO STAGES IN THE DEVELOPMENT OF APUS CANCRIFORM1S.
(After Claus.)
A. Nauplius stage at the time of hatching.
B. Stage after first ecdysis.
an 1 , and a 2 . First and second antennae ; md. mandible ; MX. maxilla ; /. labrum;
fr. frontal sense organ ; /. caudal fork ; s. segments.
The term has now been extended to a very large number of
larvae which have certain definite characters in common. They
are provided (fig. 208 A) with three pairs of appendages, the
future two pairs of antennae and mandibles. The first pair of
antennae (an 1 ) is uniramous and mainly sensory in function, the
second pair of antennae (an*) and mandibles (md) are biramous  swimming appendages, and the mandibles are without the future
cutting blade. The Nauplius mandibles represent in fact the
palp. The two posterior appendages are both provided with
hook-like prominences on their basal joints, used in mastication.
The body in most cases is unsegmented, and bears anteriorly a
single median eye. There is a large upper lip, and an alimentary canal formed of cesophagus, stomach and rectum. The anus
opens near the hind end of the body. On the dorsal surface
small folds of skin frequently represent the commencement of a
dorsal shield. One very striking peculiarity of the Nauplius
according to Claus and Dohrn is the fact that the second pair
of antennae is innervated from a sub-oesophageal ganglion. A
larval form with the above characters occurs with more or less
frequency in all the Crustacean groups. In most instances it does not exactly conform to the above type, and the divergences
are more considerable in the Phyllopods than in most other
groups. Its characters in each case are described in the sequel.
Phyllopoda. For the Phyllopoda the development of Apus
cancriformis may conveniently be taken as type (Claus, No. 454).
The embryo at the time it leaves the egg (fig. 208 A) is somewhat oval in outline, and narrowed posteriorly. There is a
slight V-shaped indentation behind, at the apex of which is
situated the anus. The body, unlike that of the typical
Nauplius, is already divided into two regions, a cephalic and
post-cephalic. On the ventral side of the cephalic region there
are present the three normal pairs of appendages. Foremost
there are the small anterior antennae (an 1 ), which are simple
unjointed rod-like bodies with two moveable hairs at their
extremities. They are inserted at the sides of the large upperlip or labrum (/). Behind these are the posterior antennae, which
are enormously developed and serve as the most important
larval organs of locomotion. They are biramous, being formed
of a basal portion with a strong hook-like bristle projecting
from its inner side, an inner unjointed branch with three bristles,
and an outer large imperfectly five-jointed branch with five long
lateral bristles. The hook-like organ attached to this pair of
appendages would seem to imply that it served in some ancestral
form as jaws (Claus). This character is apparently universal in
the embryos of true Phyllopods, and constantly occurs in the
Copepoda, etc.
The third pair of appendages or mandibles (md) is attached
close below the upper lip. They are as yet unprovided with
cutting blades, and terminate in two short branches, the inner
with two and the outer with three bristles.
At the front of the head there is the typical unpaired eye.
On the dorsal surface there is already present a rudiment of the
cephalic shield, continuous anteriorly with the labrum (/) or
upper lip, the extraordinary size of which is characteristic of the
larvae of Phyllopods. The post-cephalic region, which afterwards
becomes the thorax and abdomen, contains underneath the skin
rudiments of the five anterior thoracic segments and their
appendages, and presents in this respect an important variation
from the typical Nauplius form. After the first ecdysis the larva (fig. 208 B) loses its oval form, mainly owing to the elongation of the hinder part of the body and the lateral extension of
the cephalic shield, which moreover now completely covers over
the head and has begun to grow backwards so as to cover over
the thoracic region. At the second ecdysis there appears at its
side a rudimentary shell gland. In the cephalic region two
small papillae (fr) are now present at the front of the head close
to the unpaired eye. They are of the nature of sense organs,
and may be called the frontal sense papillae. They have been
shewn by Claus to be of some phylogenetic importance. The
three pairs of Nauplius appendages have not altered much, but
a rudimentary cutting blade has grown out from the basal joint
of the mandible. A gland opening at the base of the antennae
is now present, which is probably equivalent to the green gland
often present in the Malacostraca. Behind the mandibles a pair
of simple processes has appeared, which forms the rudiment of
the first pair of maxillae (mx).
In the thoracic region more segments have been added
posteriorly, and the appendages of the three anterior segments
are very distinctly formed. The tail is distinctly forked. The
heart is formed at the second ecdysis, and then extends to the
sixth thoracic segment : the posterior chambers are successively
added from before backwards.
At the successive ecdyses which the larva undergoes new
segments continue to be formed at the posterior end of the body,
and limbs arise on the segments already formed. These limbs
probably represent the primitive form of an important type of
Crustacean appendage, which is of value for interpreting the
parts of the various malacostracan appendages. They consist
(fig. 209) of a basal portion (protopodite of Huxley) bearing two
rami. The basal portion has two projections on the inner side.
To the outer side of the basal portion there is attached a
dorsally directed branchial sack (br) (epipodite of Huxley). The
outer ramus (ex) (exopodite of Huxley) is formed of a single plate
with marginal setae. The inner one (en) (endopodite of Huxley)
is four-jointed, and a process similar to those of the basal joint
is given off from the inner side of the three proximal joints.
At the third ecdysis several new features appear in the
cephalic region, which becomes more prominent in the succeeding stages. In the first place the paired eyes are formed at each side
of and behind the unpaired eye, second
ly the posterior pair of maxillae is
formed though it always remains very
rudimentary. The shell gland becomes
fully developed opening at the base of
the first pair of maxillae. The dorsal
shield gradually grows backwards till it
covers its full complement of segments.
After the fifth ecdysis the Nauplius
FIG. 209. TYPICAL PHYLLOPOD APPENDAGE. (Copied appendages undergo a rapid atrophy. f rom ciaus.)
The second pair of antennae especially ex. exopodite ; en. endo
becomes reduced in size, and the man
dibular palp the primitive Nauplius portion bearing the two proxir . ..... , mal projections is not sharply
portion of the mandible is contracted separated from the endopoto a mere rudiment, which eventually dite completely disappears, while the blade is correspondingly enlarged and also becomes toothed. The adult condition is only
gradually attained after a very large number of successive changes
of skin.
The chief point of interest in the above development is the
fact of the primitive Nauplius form becoming gradually converted without any special metamorphosis into the adult condition 1 .
Branchipus like Apus is hatched as a somewhat modified Nauplius,
which however differs from that of Apus in the hinder region of the body
having no indications of segments. It goes through a very similar metamorphosis, but is at no period of its metamorphosis provided with a dorsal
shield : the second pair of antennae does not abort, and in the male is provided with clasping organs, which are perhaps remnants of the embryonic
hooks so characteristic of this pair of antennas.
The larva of Estheria when hatched has a Nauplius form, a large
upper lip, caudal fork and single eye. There are two functional pairs of
swimming appendages the second pair of antennae and mandibles. The
first pair of antennae has not been detected, and a dorsal mantle to form
the shell is not developed. At the first moult the anterior pair of
antennae arises as small stump-like structures, and a small dorsal shield
is also formed. Rudiments of six or seven pairs of appendages sprout
1 Nothing appears to be known with reference to the manner in which it comes
about that more than one appendage is borne on each of the segments from the
eleventh to the twentieth. An investigation of this point would be of some interest
with reference to the meaning of segmentation
out in the usual way, and continue to increase in number at successive
moults : the shell is rapidly developed. The chief point of interest in
the development of this form is the close resemblance of the young larva
to a typical adult Cladocera (Claus). This is shewn in the form of the
shell, which has not reached its full anterior extension, the rudimentary
anterior antennae, the large locomotor second pair of antennas, which differ
however from the corresponding organs in the Cladocera in the presence
of typical larval hooks. Even the abdomen resembles that of Daphnia.
These features perhaps indicate that the Cladocera are to be derived
from some Phyllopod form like Estheria by a process of retrogressive
metamorphosis. The posterior antennas in the adult Estheria are large
biramous appendages, and are used for swimming ; and though they
have lost the embryonic hook, they still retain to a larger extent than
in other Phyllopod families their Nauplius characteristics.
The Nauplius form of the Phyllopods is marked by several
definite peculiarities. Its body is distinctly divided into a cephalic and post-cephalic region. The upper lip is extraordinarily
large, relatively very much more so than at the later stages.
The first pair of antennae is usually rudimentary and sometimes
even absent ; while the second pair is exceptionally large, and
would seem to be capable of functioning not only as a swimming
organ, but even as a masticating organ. A dorsal shield is
nearly or quite absent.
Cladocera. The probable derivation of the Cladocera from a form
similar to Estheria has already been mentioned, and it might have been
anticipated that the development would be similar
to that of the Phyllopods.
The development of the majority of the Cladocera takes
place however in the egg,
and the young when hatched
closely resembles their parents, though in the egg they
pass through a Nauplius
stage (Dohrn). An exception to the general rule is
however offered by the case
of the winter eggs of Leptodora, one of the most primitive of the Cladoceran
families. The summer eggs after Sars.)
FIG. 709 A. NAUPLIUS LARVA OF LEPTODORA
IIYAI.INA FROM wiNTKR EGG. (Copied from Bronn ;
develop without metamor
;/'. antenna of first pair; an*, antenna of
phosis, but Sars (No. 461) second pair; ntd. mandible;/ caudal fork.
has discovered that the larva leaves the winter eggs in the form of a
Nauplius (fig. 209). This Nauplius closely resembles that of the Phyllopods.
The body is elongated and in addition to normal Nauplius appendages
is marked by six pairs of ridges the indications of the future feet. The
anterior antennae are as usual small ; the second large and biramous,
but the masticatory bristle characteristic of the Phyllopods is not present.
The mandibles are without a cutting blade. A large upper lip and unpaired
eye are present.
The adult form is attained in the same manner as amongst the Phyllopods after the third moult.
MALACOSTRACA.
Owing to the size and importance of the various forms
included in the Malacostraca, greater attention has been paid to
their embryology than to that of any other division of the
Crustacea ; and the proper interpretation of their larval forms
involves some of the most interesting problems in the whole
range of Embryology.
The majority of Malacostraca pass through a more or less
complicated metamorphosis, though in the Nebaliadae, the
Cumaceae, some of the Schizopoda, a few Decapoda (Astacus,
Gecarcinus, etc.), and in the Edriophthalmata, the larva on
leaving the egg has nearly the form of the adult. In contradistinction to the lower groups of Crustacea the Nauplius form of
larva is rare, though it occurs in the case of one of the Schizopods
(Euphausia, fig. 212), in some of the lower forms of the Decapods
(Penaeus, fig. 214), and
perhaps also, though this
has not been made out, in
some of the Stomatopoda.
In the majority of the
Decapoda the larva leaves
the egg in a form known
as the Zoaea (fig. 210).
This larval form is
characterised by the presence of a large cephalo
thoracic t shield usually FIG. 210. ZO^EAOFTHIAPOLITA. (After'Claus.)
, ., , , , , mxp*. second maxillipede.
armed with lateral, anterior, and dorsal spines. The caudal segments are well de
B. II. 30
466 SCHIZOPODA.
veloped, though wit/tout appendages, and the tail, which functions
in swimming, is usually forked. The six posterior thoracic segments are, on the other hand, rudimentary or non-existent. There
are seven anterior pairs of appendages shewn in detail in fig. 21 1,
viz. the two pairs of antennae (At. I. and At. II.), neither of them
used as swimming organs, the mandibles without a palp (ma 7 ),
well-developed maxillae (two pairs, mx I and mx 2), and two or
sometimes (Macrura) three pairs of biramous natatory maxillipeds (mxp I and mxp 2). Two lateral compound stalked eyes
are present, together with a median Nauplius eye. The heart
has in the majority of cases only one or two (Brachyura) pairs of
ostia.
The Zoaea larva, though typically developed in the Decapoda,
is not always present (e.g. Astacus and Homarus), and some
FIG. 211. THE APPENDAGES OF A CRAB Z<VEA.
.-//./. first antenna ; At. I I. second antenna ; md. mandible (without a palp); mx.
\. first maxilla; mx. i. second maxilla; mxp. \. first maxilliped ; mxp. i. second
maxilliped.
ex. exopodite ; en. endopodite.
times occurs in a very modified form. It makes its appearance
in an altered garb in the ontogeny of some of the other groups.
The two Malacostracan forms, amongst those so far studied,
in which the phylogenetic record is most fully preserved in the
ontogeny, are Euphausia amongst the Schizopods and Penaeus
amongst the Decapods.
Schizopoda. Euphausia leaves the egg (MetschnikofT, No. 4689)
as a true Nauplius with only three pairs of appendages, the two hinder
CRUSTACEA.
467
biramous, and an unsegmented body. The second pair of antennae has not
however the colossal dimensions so common in the lower types. A mouth is
present, but the anus is undeveloped.
After the first moult three pairs of prominences the rudiments of the
two maxillae and ist maxillipeds arise behind the Nauplius appendages
(fig. 212). At the same time an anus appears between the two limbs of
a rudimentary caudal fork ; and an unpaired eye and upper lip appear in
front. After another moult (fig. 212) a lower lip is formed (UL) as a
pair of prominences very similar to true appendages ; and a delicate
cephalo-thoracic shield also becomes developed. Still later the cutting blade
of the mandible is formed, and the palp (Nauplius appendage) is greatly
FIG. 212. NAUPLIUS OF EUPHAUSIA. (From Glaus; after Metschnikoff.)
The Nauplius is represented shortly before an ecdysis, and in addition to the
proper appendages rudiments of the three following pairs are present.
OL. upper lip ; UL. lower lip ; Md. mandible ; MX', and MX", two pairs of
maxillae ; mf . maxilliped i .
reduced. The cephalo-thoracic shield grows over the front part of the
embryo, and becomes characteristically toothed at its edge. There are also
302
468 SCHIZOPODA.
two frontal papillae very similar to those already described in the Phyllopod
larvae. Rudiments of the compound eyes make their appearance, and
though no new appendages are added, those already present undergo further
differentiations. They remain however very simple ; the maxillipeds
especially are very short and resemble somewhat Phyllopod appendages.
Up to this stage the tail has remained rudimentary and short, but
after a further ecdysis (Claus) it grows greatly in length. At the same
time the cephalo-thoracic shield acquires a short spine directed backwards.
The larva is now in a condition to which Claus has given the name of
Protozoasa (fig. 213 A).
Very shortly afterwards the region immediately following the segments
already formed becomes indistinctly segmented, while the tail is still without a trace of segmentation. The region of the thorax proper soon becomes distinctly divided into seven very short segments, while at the same
time the now elongated caudal region has become divided into its normal
number of segments (fig. 213 B). By this stage the larva has become
FIG. 213. LARVAE OF EUPHAUSIA. (After Claus.) From the side.
A. Protozorea larva. B. Zonea larva.
mx'. and tux", maxillre I and 2 ; mxp^. maxilliped r.
a true Zoaea though differing from the normal Zoaea in the fact that
the thoracic region is segmented, and in the absence of a second pair of
maxillipeds.
The adult characters are very gradually acquired in a series of successive moults ; the later development of Euphausia resembling in this
respect that of the Phyllopods. On the other hand Euphausia differs from
that group in the fact that the abdominal (caudal) and thoracic appendages
develop as two independent series from before backwards, of which the
abdominal series is the earliest to attain maturity.
CRUSTACEA.
469
This is shewn in the following table compiled from Claus' observations.
LENGTH OF LARVA.
APPENDAGES OF THORACIC
REGION ; viz. the 2nd and
3rd maxilliped and 5 ambu
latory appendages.
APPENDAGES OF ABDOMEN.
3 3^ mm.
2nd maxilliped, rudimentary.
ist abdominal appendage.
3 4 mm.
2nd maxilliped, biramous.
3rd rudimentary,
ist and 2nd ambulatory appendages, rudimentary.
2nd and 3rd abdominal appendages.
4th and 5th rudimentary.
4^ 5 mm.
3rd maxilliped, biramous.
4 th, 5th, and 6th fully developed.
55^ mm.
3rd and 4th ambulatory appendages.
6 mm.
5th ambulatory appendage.
All the appendages following the second pair of maxillas are biramous,
and the first eight of these bear branched gills as their epipodites. It is
remarkable that the epipodite is developed on all the appendages anteriorly
in point of time to the outer ramus (exopodite).
Although in Mysis there is no free larval stage, and the development
takes place in a maternal incubatory pouch, yet a stage may be detected
which clearly corresponds with the Nauplius stage of Euphausia (E. van
Beneden, No. 465). At this stage, in which only the three Nauplius
appendages are developed, the Mysis embryo is hatched. An ecdysis
takes place, but the Nauplius skin is not completely thrown off, and
remains as an envelope surrounding the larva during its later development.
Decapoda. Amongst the Decapoda the larva usually leaves
the egg in the Zoaea form, but a remarkable exception to this
general rule is afforded by the case of one or more species of
Penseus. Fritz M tiller was the first to shew that the larva of
these forms leaves the egg as a typical Nauplius, and it is
probable that in the successive larval stages of these forms the
ancestral history of the Decapoda is most fully preserved 1 .
The youngest known larva of Penaeus (fig. 214) has a somewhat oval unsegmented body. There spring from it the three
typical pairs of Nauplius appendages. The first is uniramous,
the second and third are biramous, and both of them adapted
1 The doubts which have been thrown upon Miiller's observations appear to be
quite unfounded.
470 DECAPODA.
for swimming, and the third of them (mandibles) is without a
trace of the future blade. The body has no carapace, and bears
anteriorly a single median simple eye. Posteriorly it is produced
into two bristles.
After the first moult the larva has a rudiment of a forked
tail, while a dorsal fold of skin indicates the commencement of
FIG. 214. NAUPLIUS STAGE OF PEN^EUS. (After Fritz Miiller.)
the cephalo-thoracic shield. A large provisional helmet-shaped
upper lip like that in Phyllopods has also appeared. Behind
the appendages already formed there are stump-like rudiments
of the four succeeding pairs (two pairs of maxillae and two pairs
of maxillipeds) ; and in a slightly older larva the formation of
the mandibular blade has commenced, together with the atrophy
of the palp or Nauplius appendage.
Between this and the next observed stage there is possibly a
slight lacuna. The next stage (fig. 215) at any rate represents
the commencement of the Zoaea series. The cephalo-thoracic
shield has greatly grown, and eventually acquires the usual
dorsal spine. The posterior region of the body is prolonged
into a tail, which is quite as long as the whole of the remainder
of the body. The four appendages which were quite functionless
at the last stage have now sprouted into full activity. The
CRUSTACEA.
471
region immediately behind them is divided (fig.
215) into six segments
(the six thoracic segments) without appendages, while somewhat
later the five anterior
abdominal segments become indicated, but are
equally with the thoracic
segments without feet.
The mode of appearance
of these segments shews
that the thoracic and
abdominal segments develop in regular succession from before backwards (Claus). Of the
palp of the mandibles,
as is usual amongst Zosea
forms, not a trace remains,
though in the youngest
Zoaea caught by Fritz
Miiller a very small rudiment of the palp was present. The
first pair of antennae is unusually long, and the second pair
continues to function as a biramous swimming organ ; the
outer ramus is multiarticulate. The other appendages are fully
jointed, and the two maxillipeds biramous. On the dorsal
surface of the body the unpaired eye is still present, but on each
side of it traces of the stalked eyes have appeared. Frontal
sense organs like those of Phyllopods are also present.
From the Protozoaea form the larva passes into that of a true
Zoaea with the usual appendages and spines, characterised however by certain remarkable peculiarities. Of these the most
important are (i) the large size of the two pairs of antennae and
the retention of its Nauplius function by the second of them ;
(2) the fact that the appendages of the six thoracic segments
appear as small biramous Schizopod legs, while the abdominal
appendages, with the exception of the sixth, are still without
FIG.
215.
PROTOZO^EA STAGE OF PEN/EUS.
(After Fritz Miiller.)
472 DECAPODA.
their swimming feet. The early appearance of the appendages
of the sixth abdominal segment is probably correlated with
their natatory function in connection with the tail. As a point
of smaller importance which may be mentioned is the fact that
both pairs of maxillae are provided with small respiratory plates
(exopodites) for regulating the flow of water under the dorsal
shield. From the Zoaea form the larva passes into a Mysis or
Schizopod stage (fig. 216), characterised by the thoracic feet and
maxillipeds resembling in form and function the biramous feet
of Mysis, the outer ramus being at first in many cases much
larger than the inner. The gill pouches appear at the base of
these feet nearly at the same time as the endopodites become
functional. At the same time the antennae become profoundly
modified. The anterior antennae shed their long hairs, and from
the inner side of the fourth joint there springs a new process,
FIG. 216. PEN^EUS LARVA IN THE MYSIS STAGE. (After Claus.)
which eventually elongates and becomes the inner flagellum.
The outer ramus of the posterior antennae is reduced to a scale,
while the flagellum is developed from a stump-like rudiment of
the inner ramus (Claus). A palp sprouts on the mandible and
the median eye disappears.
The abdominal feet do not appear till the commencement of
the Mysis stage, and hardly become functional till its close.
From the Mysis stage the larva passes quite simply into the
adult form. The outer ramus of the thoracic feet is more or less
completely lost. The maxillipeds, or the two anterior pairs at
any rate, lose their ambulatory function, cutting plates develop
on the inner side of their basal joints, and the two rami persist
CRUSTACEA.
473
as small appendages on their outer side. Gill pouches also
sprout from their outer side.
The respiratory plate of the second maxilla attains its full
development and that on the first maxilla disappears 1 . The
Nauplius, so far as is known, does not occur in any other
Decapod form except Penaeus.
The next most primitive
larval history known is
that which appears in the
Sergestidae. The larval
history, which has been
fully elucidated by Claus,
commences with a Protozoaea form (fig. 217), which
develops into a remarkable
Zoaea first described by
Dohrn as Elaphocaris.
This develops into a form
originally described by
Claus as Acanthosoma,
and this into a form known
as Mastigopus (fig. 218)
from which it is easy to
pass to the adult.
The remarkable Protozoaea (fig. 217) is characterised by the presence on
the dorsal shield of a frontal, dorsal and two lateral
spikes, each richly armed
with long side spines. The
FIG. 217. LATEST PROTOZO^A STAGE OF SEK
GESTES LARVA (ELAPHOCARIS). (After Claus.)
mxp'" '. third pair of maxillipeds.
normal Zoasa appendages are present, and in addition to them a small third
pair of maxillipeds. The thoracic region is divided into five short rings, but
the abdomen is unsegmented. The tail is forked and provided with long
spines. The antennae, like those of Penasus, are long the second pair
biramous ; the mandibles unpalped. Both pairs of maxillae are provided
with respiratory plates ; the second pair is footlike, and has at its base a
glandular mass believed by Claus to be the equivalent of the Entomostracan
shell-gland. The maxillipeds have the usual biramous characters. A
1 From Claus' observations (No. 448) it would appear that the respiratory plate
is only the exopodite and not, as is usually stated, the coalesced exopodite and
epipodite. Huxley in his Comparative Anatomy reserves this point for embryological
elucidation.
474
DECAPOD A.
FIG. 218. MASTIGOPUS STAGE
OF SERGESTES. (From Claus.)
Mf". maxilliped 3.
helmet-shaped upper lip like
that of a typical Nauplius is
present, and the eyes are situated on very long stalks.
In the true Zoaea stage there
appear on the five thoracic
segments pouch-like biramous rudiments of the limbs. The
tail becomes segmented; but the segments, with the
exception of the sixth, remain without appendages. On
the sixth a very long bilobed pouch appears as the commencement of the swimming feet of this segment. The
segments of the abdomen are armed with lateral spines.
From the Zoaea stage the larva passes into the form
known as Acanthosoma, which represents the Mysis stage
of Penaeus. The complex spikes on the dorsal shield of
the Zoaea stage are reduced to simple spines, but the
spines of the tail still retain their full size. In the appendages the chief
changes consist (i) in the reduction of the jointed outer ramus of the
second pair of antennae to a stump representing the scale, and the elongation of the inner one to the flagellum ; (2) in the elongation of the five
ambulatory thoracic appendages into biramous feet, like the maxillipeds,
and in the sprouting forth of rudimentary abdominal feet.
CRUSTACEA.
475
The most obvious external indications of the passage from the Acanthosoma to the Mastigopus stage (fig. 218)
are to be found in the elongation of the
abdomen, the reduction and flattening
of the cephalo-thoracic shield, and the
nearly complete obliteration of all the
spines but the anterior. The eyes on
their elongated stalks are still very
characteristic, and the elongation of
the flagellum of the second pair of
antennae is very striking.
The maxillae and maxillipeds undergo considerable metamorphosis, the
abdominal feet attain their adult form,
and the three anterior thoracic ambulatory legs lose their outer rami. The
most remarkable change of all concerns
the two last pairs of thoracic appendages, which, instead of being metamorphosed like the preceding ones, are
completely or nearly completely thrown
off in the moult which inaugurates the
Mastigopus stage, and are subsequently
redeveloped. With the reappearance
of these appendages, and the changes
in the other appendages already indicated, the adult form is practically
attained.
FIG. 219. LARVA OF HIPPOLYTE
IN ZO/EA STAGE. (From Claus.)
MX', and MX", maxillae i and 2 ;
Mf. Mf. Mf". maxillipeds.
FIG. 220.
OLDER LARVA OF HIPPOLYTE AFTER THE THORACIC APPENDAGES HAVE
BECOME FORMED. (From Claus.)
476 DECAPODA.
With reference to the development of the majority of the
Carabidae, Penaeinae, Palaemoninae, Crangoninae, it may be stated
generally that they leave the egg in the Zoaea stage (fig. 219)
with anterior appendages up to the third pair of maxillipeds.
The thorax is unsegmented and indeed almost unrepresented,
but the abdomen is long and divided into distinct segments.
Both thoracic and abdominal appendages are absent, and the
tail is formed by a simple plate with numerous bristles, not
forked, as in the case of the Zoaea of Fritz M tiller's Penaeus and
Sergestes. A dorsal spine is frequently found on the second
abdominal segment. From the Zoaea form the embryo passes
into a Mysis stage (fig. 220), during which the thoracic appendages gradually appear as biramous swimming feet; they
FIG. 221. NEWLY-HATCHED LARVA OF THE AMERICAN LOBSTER. (After Smith.)
are all developed before any of the abdominal appendages,
except the last. In some cases the development is still further
abbreviated. Thus the larvae of Crangon and Palaemonetes
(Faxon, No. 476) possess at hatching the rudiments of the two
anterior pairs of thoracic feet, and Palaemon of three pairs'.
Amongst the other Macrura the larva generally leaves the
egg as a Zoaea similar to that of the prawns. In the case of the
1 Fritz Miiller has recently (Zoologisrher Anzeiger^ No. 52) described a still more
abbreviated development of a Pala-mon living in brooks near Blumenau.
CRUSTACEA. 477
Thalassinidae and Paguridae a Mysis stage has disappeared.
The most remarkable abbreviations of the typical development
are presented on the one hand by Homarus and Astacus, and on
the other by the Loricata.
The development of Homarus has been fully worked out by S. J. Smith
(No. 491) for the American lobster (Homarus americanus). The larva (fig.
221) leaves the egg in an advanced Mysis stage. The cephalo-thoracic
shield is fully developed, and armed with a rostrum in front. The first pair
of antennae is unjointed but the second is biramous, the outer ramus forming
a large Mysis-like scale. The mandibles, which are palped, the maxillae,
and the two anterior maxillipeds differ only in minor details from the same
appendages of the adult. The third pair of maxillipeds is Mysis-like and
biramous, and the five ambulatory legs closely resemble them, the endopodite of the first being imperfectly chelate. The abdomen is well developed
but without appendages. The second, third, fourth and fifth segments are
armed with dorsal and lateral spines.
In the next stage swimming feet have appeared on the second, third,
fourth and fifth abdominal segments, and the appendages already present
have approached their adult form. Still later, when the larva is about half
an inch in length, the approach to the adult form is more marked, and the
exopodites of the ambulatory legs though present are relatively much
reduced in size. The swimmerets of the sixth abdominal segment are
formed. In the next stage observed the larva has entirely lost its Schizopod
characters, and though still retaining its free swimming habits differs from
the adult form only in generic characters.
As has been already stated, no free larval stages occur in the development of Astacus, but the young is hatched in a form in which it differs only
in unimportant details from the adult.
The peculiar larval form of the Loricata (Scyllarus, Palinurus) has long
been known under the name Phyllosoma (fig. 222 C), but its true nature was
first shewn by Couch (No. 474) [Couch did not however recognise the
identity of his larva with Phyllosoma ; this was first done by Gerstacker]
and shortly afterwards by Gerbe and Coste. These observations were
however for a long time not generally accepted, till Dohrn (No. 477)
published his valuable memoir giving an account of how he succeeded in
actually rearing Phyllosoma from the eggs of Scyllarus and Palinurus, and
shewing that some of the most remarkable features of the metamorphosis of
the Loricata occur before the larva is hatched.
The embryo of Scyllarus in the egg first of all passes through the usual
Nauplius stage, and then after the formation of a cuticle develops an
elongated thoracico-abdominal region bent completely over the anterior
part of the body. There appear moreover a number of appendages and the
rudiments of various organs ; and the embryo passes into a form which may
be described as the embryonic Phyllosoma stage. In this stage there are
present on the anterior part of the body, in front of the ventral flexure, two
478 DECAPODA.
pairs of antennae, mandibles, two pairs of maxillae, the second commencing
to be biramous, and a small stump representing the first pair of maxillipeds.
The part of the body bent over consists of a small quadrate caudal plate,
and an appendage-bearing region to which are attached anteriorly three
pairs of biramous appendages the second and third maxillipeds, and the
anterior pair of ambulatory legs and two pairs of undivided appendages
the second and third pairs of ambulatory legs. In a slightly later stage the
first pair of maxillae becomes biramous, as also does the first pair of maxillipeds in a very rudimentary fashion. The second and third pairs of ambulatory legs become biramous, while the second and third maxilliped nearly
completely lose their outer ramus. Very small rudiments of the two hinder
ambulatory legs become formed. If the embryo is taken at this stage (vide
fig. 222 A, which represents a nearly similar larva of Palinurus) out of the
egg, it is seen to consist of (i) an anterior enlargement with a vaulted dorsal
shield enclosing the yolk, two stalked eyes, and a median eye ; (2) a thoracic
region in which the indications of segmentation are visible with the two
FIG. 222. LARWE OF THE LORICATA. (After Claus.)
A. Embryo of Palinurus shortly before hatching.
B. Young Phyllosoma larva of Scyllarus, without the first maxilliped, the two
last thoracic appendages, or the abdominal appendages.
C. Fully-grown Phyllosoma with all the Decapod appendages.
at*, antenna of first pair ; at*, antenna of second pair ; md. mandible ; ntx 1 . first
maxilla; mx 1 . second maxilla; mx^mxf. maxillipeds; / 1 / 3 . thoracic
appendages.
posterior pairs of maxillipeds (mxfp and wr/ 3 ) and the ambulatory legs (/ l );
(3) an abdominal region distinctly divided into segments and ending in a fork.
Before the embryo becomes hatched the first pair of maxillipeds becomes
reduced in size and finally vanishes. The second pair of maxillae becomes
reduced to simple stumps with a few bristles, the second pair of antennae
CRUSTACEA. 479
also appears to undergo a retrogressive change, while the two last thoracic
segments cease to be distinguishable. It thus appears that during embryonic
life the second pair of antennae, the second pair of maxillae, and the second
and third pair of maxillipeds and the two hinder ambulatory appendages
undergo retrogressive changes, while the first pair of maxillipeds is completely
obliterated !
The general form of the larva when hatched (fig. 222 B) is not very
different from that which it has during the later stages within the egg. The
body is divided into three regions: (i) an anterior cephalic; (2) a middle
thoracic, and (3) a small posterior abdominal portion ; and all of them are
characterised by their extreme dorso-ventral compression, so that the whole
animal has the form of a three-lobed disc, the strange appearance of which
is much increased by its glass-like transparency.
The cephalic portion is oval and projects slightly behind so as to overlap
the thorax. Its upper surface constitutes the dorsal shield, from which there
spring anteriorly the two compound eyes on long stalks, between which is a
median Nauplius eye. The mouth is situated about the middle of the under
surface of the anterior disc. It leads into a stomach from which an anterior
and a lateral hepatic diverticulum springs out on each side. The former
remains as a simple diverticulum through larval life, but the latter becomes
an extremely complicated glandular structure.
At the front border of the disc is placed the unjointed but elongated
first pair of antennae (rt/ 1 ). Externally to and behind these there spring the
short posterior antennae (at'*}. At the base of which the green gland is
already formed. Surrounding the mouth are the mandibles (md) and anterior
pair of maxillae (mx 1 ), and some distance behind the second pair of maxillae
(mx*), consisting of a cylindrical basal joint and short terminal joint armed
with bristles. The first pair of maxillipeds is absent.
The thoracic region is formed of an oval segmented disc attached to the
under surface of the cephalic disc. From its front segment arises the second
pair of maxillipeds (inxp l } as single five-jointed appendages, and from the
next segment springs the five-jointed elongated but uniramous third pair
of maxillipeds (mxfl 3 }, and behind this there arise three pairs of six-jointed
ambulatory appendages (p\ / 2 , p 3 , of which only the basal joint is represented
in the figure) with an exopodite springing from their second joint. The two
posterior thoracic rings and their appendages cannot be made out.
The abdomen is reduced to a short imperfectly segmented stump, ending
in a fork, between the prongs of which the anus opens. Even the youngest
larval Phyllosoma, such as has just been described, cannot be compared with a
Zoaea, but belongs rather, in the possession of biramous thoracic feet, to a
Mysis stage. In the forked tail and Nauplius eye there appear however to
be certain very primitive characters carried on to this stage.
The passage of this young larva to the fully formed Phyllosoma (fig.
222 C) is very simple. It consists essentially in the fresh development of
the first pair of maxillipeds and the two last ambulatory appendages, the
growth and segmentation of the abdomen, and the sprouting on it of biramous
480 DECAPODA.
swimming feet. In the course of these changes the larva becomes a true
Decapod in the arrangement and number of its appendages ; and indeed it
was united with this group before its larval character was made out. In
addition to the appearance of new appendages certain changes take place in
those already present. The two posterior maxillipeds, in the Palinurus
Phyllosoma at any rate, acquire again an exopodite, and together with the
biramous ambulatory feet develop epipodites in the form of gill pouches.
The mode of passage of the Phyllosoma to the adult is not known, but
it can easily be seen from the oldest Phyllosoma forms that the dorsal
cephalic plate grows over the thorax, and gives rise to the cephalo-thoracic
shield of the adult.
There are slight structural differences, especially in the antennae, between
the Phyllosoma of Scyllarus and that of Palinurus, but the chief difference
in development is that the first pair of maxillipeds of the Palinurus embryo,
though reduced in the embryonic state, does not completely vanish, at any
rate till after the free larval state has commenced ; and it is doubtful if
it does so even then. The freshly hatched Palinurus Phyllosoma is very
considerably more developed than that of Scyllarus.
Brachyura. All the Brachyura, with the exception of one or
more species of land crabs 1 , leave the egg in the Zoaia condition,
and though there are slight variations of structure, yet on the
FIG. 223. THE APPENDAGES OF A CRAB ZOJEA.
At. I. first antenna ; At. //. second antenna ; md. mandible (without a palp) ; mx.
i. first maxilla ; mx. i. second maxilla ; w.r. 3. third maxilla ; mxp. i. first maxilliped ;
mxp. i. second maxilliped.
ex. exopodite ; ett. cndopodite.
whole the Crab Zoaea is a very well marked form. Immediately
after leaving the egg (fig. 210) it has a somewhat oval shape
1 It has been clearly demonstrated that the majority of land-crabs leave the egg in
the 7.oxa. form.
CRUSTACEA. 481
with a long distinctly-segmented abdomen bent underneath the
thorax. The cephalo-thoracic shield covers over the front part
of the body, and is prolonged into a long frontal spine pointing
forwards, and springing from the region between the two eyes ;
a long dorsal spine pointing backwards ; and two lateral spines.
To the under surface of the body are attached the anterior
appendages up to the second maxilliped, while the six following
pairs of thoracic appendages are either absent or represented
only in a very rudimentary form. The abdomen is without
appendages.
The anterior antennae are single and unjointed, but provided
at their extremity with a few olfactory hairs (only two in
Carcinus Mcenas) and one or two bristles. The rudiment of the
secondary flageltum appears in very young Zoaeae on the inner
side of the antennules (fig. 223 At. /.). The posterior antennae
are without the flagellum, but are provided with a scale representing the exopodite (fig. 223 At. II. ex] and usually a spinous
FIG. 224. CRAB ZO^EA AFTER TH.. THIRD PAIR OF MAXILLIPEDS AND THE
THORACIC AND ABDOMINAL APPENDAGES HAVE BECOME DEVELOPED.
at 1 , antenna of first pair ; at z . antenna of second pair ; mx l . first maxilla ; mop.
second maxilla ; mxp 1 . first maxilliped ; mxjP. second maxilliped ; mxf. third maxilliped ; oc. eye ; ht. heart.
process. The flagellum is very early developed and is represented in fig. 223, At. II. en. The mandibles (md) are large but
without a palp. The anterior maxillae (mx i) have a short twojointed endopodite (palp) with a few hairs, and a basal portion
B. II. 31
-
482 DECAPODA.
with two blades, of which the distal is the largest, both armed
with stiff bristles. The posterior maxillae have a small respiratory plate (exopodite), an endopodite (palp) shaped like a
double blade, and two basal joints each continued into a double
blade. The two maxillipeds (inxp i and mxp 2) have the form
and function of biramous swimming feet. The exopodite of
both is two-jointed and bears long bristles at its extremity ; the
endopodite of the anterior is five-jointed and long, that of the
second is three-jointed and comparatively short.
In the six-jointed tail the second segment has usually two
dorsally directed spines, and the three succeeding segments each
of them two posteriorly directed. The telson or swimming plate
is not at first separated from the sixth segment ; on each side it
is prolonged into two well-marked prongs ; and to each prong
three bristles are usually attached (fig. 224). The heart (fig.
224 ht) lies under the dorsal spine and is prolonged into an
anterior, posterior, and dorsal aorta. It has only two pairs of
venous ostia.
During the Zoaea stage the larva rapidly grows in size, and
undergoes considerable changes in its appendages which reach
the full Decapod number (fig. 224). On both pairs of antennae
a flagellum becomes developed and grows considerably in length.
Before the close of the Zoaea condition a small and unjointed
palp appears on the mandible. Behind the second maxilliped
the third maxilliped (inxp*} early appears as a small biramous
appendage, and the five ambulatory feet become distinctly
formed as uniramous appendages the exopodites not being
present. The third pair of maxillipeds and three following
ambulatory appendages develop gill pouches. The abdominal
feet are formed on the second to the sixth segments of the tail
as simple pouches.
The oldest Zoaea is transmuted at its moult into a form
known as Megalopa, which is really almost identical with an
anomurous Decapod. No Schizopod stage is intercalated, which
shews that the development is in many respects greatly abbreviated. The essential characters of the Megalopa are to be found
in (i) the reduction of the two anterior maxillipeds, which
cease to function as swimming feet, and together with the
appendages in front of them assume the adult form ; (2) the full
CRUSTACEA. 483
functional development of the five ambulatory appendages ;
(3) the reduction of the forked telson to an oval swimming
plate, and the growth in size of the abdominal feet, which
become large swimming plates and are at the same time
provided with short endopodites which serve to lock the feet of
the two sides.
With these essential characters the form of the Megalopa differs considerably in different cases. In some instances (e.g. Carcinus mcenas) the
Zoasa spines of the youngest Megalopa are so large that the larva appears
almost more like a Zoasa than a Megalopa (Spence Bate, No. 470). In other
cases, e.g. that represented on fig. 225, the Zoasa spines are still present but
much reduced; and the cephalo-thoracic shield has very much the adult
form. In other cases again (e.g. Portunus) the Zoasa spines are completely
thrown off at the youngest Megalopa stage.
There is a gradual passage from the youngest Megalopa to
the adult form by a series of moults.
Some of the brachyurous Zoasa forms exhibit
considerable divergences
from the described type,
more espcially in the armature of the shield. In
some forms the spines are
altogether absent, e.g. Maja
(Couch, No. 474) and Eurynome. In other forms
the frontal spine may be
much reduced or absent
(Inachus and Achasus).
The dorsal spine may also
be absent, and in one form
described by Dohrn (No.
478) there is a long frontal
spine and two pairs of
lateral spines, but no dorsal ^ MEGALOPA STAGE OF CRAB LARVA.
spine. Both dorsal and
frontal spines may attain enormous dimensions and be swollen at their extremities (Dohrn). A form has been described by Claus as Pterocaris in which
the cephalo-thoracic shield is laterally expanded into two wing-like processes.
The Zoasa of Porcellana presents on the whole the most remarkable
peculiarities and, as might be anticipated from the systematic position of the
adult, is in some respects intermediate between the macrurous Zoasa and that
of the Brachyura. It is characterized by the oval form of the body, and by
31-2
484 STOMATOPODA.
the presence of one enormously long frontal spine and two posterior spines.
The usual dorsal spine is absent. The tail plate is rounded and has the
character of the tail of a macrurous Zoaea, but in the young Zoasa the third
pair of maxillipeds is absent and the appendages generally have a brachyurous character. A Megalopa stage is hardly represented, since the adult
may almost be regarded as a permanent Megalopa.
Stomatopoda. The history of the larval forms of the Stomatopoda
(Squilla etc.) has not unfortunately been thoroughly worked out, but what is
known from the researches of Fritz Miiller (No. 495) and Claus (No. 494) is
of very great importance. There are it appears two types, both of which
used to be described as adult forms under the respective names Erichthus
and Alima.
The youngest known Erichthus form is about two millimetres in length,
and has the characters of a modified Zoaea (fig. 226). The body is divided
into three regions, an anterior unsegmented region to which are attached
two pairs of antennas, mandibles, and maxillae (two pairs). This portion
has a dorsal shield covering the next or middle region, which consists of
five segments each with a pair of biramous appendages. These appendages
represent the five maxillipeds of the adult 1 . The portion of the body
behind this is without appendages. It consists of three short anterior
segments, the three posterior thoracic segments of the adult, and a long
unsegmented tail. The three footless thoracic segments are covered by the
dorsal shield. Both pairs of antennae are uniramous and comparatively
short. The mandibles, like those of Phyllopods, are without palps, and the
two following pairs of maxillae are small. The five maxillipeds have the
characters of normal biramous Zoaea feet. From the front of the head
spring a pair of compound eyes with short stalks, which grow longer
in the succeeding stages ; between them is a median eye. The dorsal
shield is attached just behind this eye, and is provided, as in the typical
Zoaea, with a frontal spike while its hinder border is produced into two
lateral spikes and one median. In a larva of about three millimetres a pair
of biramous appendages arises behind the three footless thoracic segments.
It is the anterior pair of abdominal feet (fig. 226). The
inner ramus of the second pair
of maxillipeds soon grows
greatly in length, indicating
its subsequent larger size and
prehensile form (fig. 227 g).
When the larva after one or
two moults attains a length FlG - 6 - SECOND STAGE OF ERICHTHUS
of six millimetres Cfitr 227 1 LARVA OFSQUII.LA WITH FIVE MAXILLIPEDS AND
(tig. 227) THE FIRST PAIR OF ABDOMINAL APPENDAGES.
the abdomen has six segments (From Claus.)
1 These five maxillipeds correspond with the three maxillipeds and two anterior
ambulatory appendages of the Decapoda.
CRUSTACEA.
485
(the sixth hardly differentiated), each with a pair of appendages (the two
hindermost still rudimentary) which have become gradually developed from
before backwards. The three hindermost thoracic segments are still without
appendages.
Some changes of importance have occurred in the other parts. Both
antennas have acquired a second flagellum, but the mandible is still without
FIG. 227. ADVANCED ERICHTHUS LARVA OF SQUILLA WITH FIVE PAIRS OF
ABDOMINAL APPENDAGES. (From Claus.)
f. first maxilliped ; g. second maxilliped.
a palp. The first and second pair of maxillipeds have both undergone
important modifications. Their outer ramus (exopodite) has been thrown
off, and a gill-plate (epipodite) has appeared as an outgrowth from their
basal joint. Each of them is composed of six joints. The three following
biramous appendages have retained their earlier characters but have become
much reduced in size. In the subsequent moults the most remarkable new
features concern the three posterior maxillipeds, which undergo atrophy, and
are either completely lost or reduced to mere unjointed sacks (fig. 228). In
FIG. 228. ADVANCED ERICHTHUS LARVA OF SQUILLA WHEN THE THREE
POSTERIOR MAXILLIPEDS HAVE BECOME REDUCED TO MINUTE POUCHES.
(From Claus.)
the stage where the complete Erichthus type has been reached, these
three appendages have again sprouted forth in their permanent form and
each of them is provided with a gill-sack on its coxal joint. Behind them
the three ambulatory appendages of the thorax have also appeared, first
as simple buds, which subsequently however become biramous. On their
development the full number of adult appendages is acquired.
The most noteworthy points in the developmental history detailed above
are the following :
(i) The thoracic and abdominal segments (apart from their appendages)
develop successively from before backwards.
486 STOMATOPODA.
(2) The three last maxillipeds develop before the abdominal feet, as
biramous appendages, but subsequently completely atrophy, and then sprout
out again in their permanent form.
(3) The abdominal feet develop in succession from before backwards,
and the whole series of them is fully formed before a trace of the appendages
of the three hindermost thoracic segments has appeared. It may be
mentioned as a point of some importance that the Zoaea of Squilla has
an elongated many-chambered heart, and not the short compact heart
usually found in the Zoaea.
The younger stages of the Alima larva are not known 1 , but the earliest
stage observed is remarkable for presenting no trace of the three posterior
pairs of maxillipeds, or of the three following pairs of thoracic appendages.
The segments belonging to these appendages are however well developed.
The tail has its full complement of segments with the normal number of
well developed swimming feet. The larva represents in fact the stage of
the Erichthus larva when the three posterior pairs of maxillipeds have
undergone atrophy ; but it is probable that these appendages never become
developed in this form of larva.
Apart from the above peculiarities the Alima form of larva closely
resembles the Erichthus form.
Nebaliadae. The development of Nebalia is abbreviated, but from
MetschnikofFs figures 2 may be seen to resemble closely that of Mysis.
The abdomen has comparatively little yolk, and is bent over the ventral
surface of the thorax. There is in the egg a Nauplius stage with three
appendages, and subsequently a stage with the Zoaea appendages.
The larva when it leaves the egg has the majority of its appendages
formed, but is still enveloped in a larval skin, and like Mysis bends its
abdomen towards the dorsal side. When the larva is finally hatched it does
not differ greatly from the adult.
Cum ace ae. The development of the Cumaceae takes place for the
most part within the egg, and has been shewn by Dohrn (No. 496) to
resemble in many points that of the Isopods. A dorsal organ is present,
and a fold is formed immediately behind this which gives to the embryo a
dorsal flexure. Both of these features are eminently characteristic of the
Isopoda.
The formation of the two pairs of antennie, mandibles, and two pairs
of maxillae and the following seven pairs of appendages takes place very
early. The pair of appendages behind the second maxilku assumes an
ambulatory form, and exhibits a Schizopod character very early, differing
in both these respects from the homologous appendages in the Isopoda.
The cephalo-thoracic shield commences to be formed when the appendages
are still quite rudimentary as a pair of folds in the maxillary region. The
1 The observations of Brooks (No. 493) render it probable that the Alima larva
leaves the egg in a form not very dissimilar to the youngest known larva.
3 His paper is unfortunately in Russian.
CRUSTACEA. 487
eyes are formed slightly later on each side of the head, and only coalesce at
a subsequent period to form the peculiar median sessile eye of the adult.
The two pairs of appendages behind the second maxillae become converted into maxillipeds, and the exopodite of the first of them becomes the
main ramus, while in the externally similar second maxilliped the exopodite
atrophies and the endopodite alone remains.
The larva is hatched without the last pair of thoracic limbs or the
abdominal appendages (which are never developed in the female), but in
other respects closely resembles the adult. Before hatching the dorsal
flexure is exchanged for a ventral one, and the larva acquires a character
more like that of a Decapod.
COPEPODA.
Natantia. The free Copepoda are undoubtedly amongst
the lowest forms of those Crustacea which are free or do not
lead a parasitic existence. Although some features of their
anatomy, such for instance as the frequent absence of a heart,
may be put down to a retrogressive development, yet, from their
retention of the median frontal eye of the Nauplius as the sole
organ of vision 1 , their simple biramous swimming legs, and other
characters, they may claim to be very primitive forms, which
have diverged to no great extent from the main line of Crustacean development. They supply a long series of transitional
steps from the Nauplius stage to the adult condition.
While still within the egg-shell the embryo is divided by two
transverse constrictions into three segments, on which the three
Nauplius appendages are developed, viz. the two pairs of
antennae and the mandibles. When the embryo is hatched the
indication of a division into segments has vanished, but the
larva is in the fullest sense a typical Nauplius 2 . There are
slight variations in the shape of the Nauplius in different genera,
but its general form and character are very constant. It has
(fig. 229 A) an oval unsegmented body with three pairs of
appendages springing from the ventral surface. The anterior of
these (at i) is uniramous, and usually formed of three joints
which bear bristles on their under surface. The two posterior
1 The Pontellidse form an exception to this statement, in that they are provided
with paired lateral eyes in addition to the median one.
2 The term Nauplius was applied to the larva of Cyclops and allied organisms by
O. F. Muller under the impression that they were adult forms.
488
COPEPODA.
pairs of appendages are both biramous. The second pair of
antennae (at 2) is the largest. Its basal portion (protopodite)
bears on its inner side a powerful hook-like bristle. The outer
ramus is the longest and many-jointed ; the inner ramus has
only two joints. The mandibles (md), though smaller than the
second pair of antennae, have a nearly identical structure. No
blade-like projection is as yet developed on their protopodite.
Between the points of insertion of the first pair of antennae is
the median eye (oc), which originates by the coalescence of two
distinct parts. The mouth is ventral, and placed in the middle
line between the second pair of antennae and the mandibles : it
FIG. 229. SUCCESSIVE STAGES IN THE DEVELOPMENT OF CYCLOPS TENUICORMS.
(Copied from Bronn ; after Claus.)
A. B. and C. Nauplius stages. D. Youngest Copepod stage. In this figure maxillae
and the two rami of the maxilliped are seen immediately behind the mandible md.
oc. eye ; at 1 , first pair of antennae ; a/ 8 , second pair of antennre ; md. mandible ;
/*. first pair of feet ; / 2 . second pair of feet ; f. third pair of feet ; //. excretory concretions in the intestine.
is provided with an unpaired upper lip. There are two bristles
at the hind end of the embryo between which the anus is placed,
and in some cases there is at this part a slight indication of the
future caudal fork.
The larva undergoes a number of successive ecdyses, at each
of which the body becomes more elongated, and certain other
CRUSTACEA. 489
changes take place. First of all a pair of appendages arises
behind the mandibles, which form the maxillae (fig. 229 B) ; at
the same time the basal joint of the maxillae develops a cuttingblade. Three successive pairs of appendages (fig. 229 C) next
become formed the so-called maxillipeds (the homologues of
the second pair of maxillae), and the two first thoracic limbs.
Each of these though very rudimentary is nevertheless bifid.
The body becomes greatly elongated, and the caudal fork more
developed.
Up to this stage of development the Nauplius appendages
have retained their primitive character almost unaltered ; but
after a few more ecdyses a sudden change takes place ; a cephalothoracic shield becomes fully developed, and the larva comes to
resemble in character an adult Copepod, from which it mainly
differs in the smaller number of segments and appendages. In
the earliest 'Cyclops' stage the same number of appendages are
present as in the last Nauplius stage. There (fig. 229 D) is a
well developed cephalo-thorax, and four free segments behind it.
To the cephalo-thoracic region the antennae, mandibles, maxillae,
the now double pair of maxillipeds (derived from the original
single pair of appendages), and first pair of thoracic appendages
(p l ) are attached. The second pair of thoracic appendages (/ 2 )
is fixed to the first free segment, and the rudiment of a third
pair (/ 3 ) projects from the second free segment. The first pair
of antennae has grown longer by the addition of new joints, and
continues to increase in length in the following ecdyses till it
attains its full adult development, and then forms the chief
organ of locomotion. The second pair of antennae is much
reduced and has lost one of its rami. The two rami of the
mandibles are reduced to a simple palp, while the blade has
assumed its full importance. The maxillae and following appendages have greatly increased in size. They are all biramous,
though the two rami are not as yet jointed. The adult state is
gradually attained after a number of successive ecdyses, at
which new segments and appendages are added, while new
joints are formed for those already present.
Parasita. The earliest developmental stages of the parasitic types
of Copepoda closely resemble those of the free forms, but, as might be
expected from the peculiarly modified forms of the adult, they present a
490
COPEPODA.
large number of secondary characters. So far as is known a more or less
modified Nauplius larva is usually preserved.
The development of Achtheres percarum, one of the Lernaeopoda parasitic
in the mouth, etc. of the common Perch, may be selected to illustrate the
mode of development of these forms. The larva leaves the egg as a much
simplified Nauplius (fig. 230 A). It has an oval body with only the two
anterior pairs of Nauplius appendages ; both of them in the rudimentary
condition of unjointed rods. The usual median eye is present, and there is
also found a peculiar sternal papilla, on which opens a spiral canal filled
with a glutinous material, which is probably derived from a gland which
disappears on the completion of the duct. The probable function of this
FIG. 330. SUCCESSIVE STAGES IN THE DEVELOPMENT OF ACHTHERES PERCARUM.
(Copied from Bronn ; after Claus. )
A. Modified Nauplius stage. B. Cyclops stage. C. Late stage of male
embryo. D. Sexually mature female. E. Sexually mature male.
at 1 , first pair of antennae; at 3 , second pair of antennae; tnd. mandible; tnx.
maxillae ; ptn 1 . outer pair of maxillipeds ; ftn^. inner pair of maxillipeds ; J> 1 . first pair
of legs ; /*. second pair of legs ; z. frontal organ ; i. intestine ; o. larval eye ; b.
glandular body ; t. organ of touch ; ov. ovary ; /. rod projecting from coalesced maxillipeds ; g. cement gland ; rs. receptaculurn seminis ; n. nervous system ; te. testis ; v.
vas deferens.
organ is to assist at a later period in the attachment of the parasite to its
host. Underneath the Nauplius skin a number of appendages are visible,
which become functional after the first ecdysis. This takes place within a
few hours after the hatching of the Nauplius, and the larva then passes from
CRUSTACEA. 491
this rudimentary Nauplius stage into a stage corresponding with the Cyclops
stage of the free forms (fig. 230 B). In the Cyclops stage the larva has an
elongated body with a large cephalo-thoracic shield, and four free posterior
segments, the last of which bears a forked tail.
There are now present eight pairs of appendages, viz. antennae (two
pairs), mandibles, maxillae, maxillipeds, and three pairs of swimming feet.
The Nauplius appendages are greatly modified. The first pair of antennae is
three-jointed, and the second biramous. The outer ramus is the longest, and
bears a claw-like bristle at its extremity. This pair of appendages is used
by the larva for fixing itself. The mandibles are small and connected with
the proboscidiform mouth ; and the single pair of maxillae is small and palped.
The maxillipeds (pm* and flm 2 ) are believed by Claus to be primitively
a single biramous appendage, but early appear as two distinct structures 1 ,
the outer and larger of which becomes the main organ by which the larva is
fixed. Both are at this stage simple two-jointed appendages. The two
anterior pairs of swimming feet have the typical structure, and consist of a
protopodite bearing an unjointed exopodite and endopodite. The first pair
is attached to the cephalo-thorax and the second (p*} to the first free thoracic
segment. The third pair is very small and attached to the second free
segment. The mouth is situated at the end of a kind of proboscis formed
by prolongations of the upper and lower lips. The alimentary tract is fairly
simple, and the anus opens between the caudal forks.
Between this and the next known stage it is quite possible that one
or more may intervene. However this may be the larva in the next stage
observed (fig. 230 C) has already become parasitic in the mouth of the Perch,
and has acquired an elongated vermiform aspect. The body is divided into
two sections, an anterior unsegmented, and a posterior formed of five
segments, of which the foremost is the first thoracic segment which in the
earlier stage was fused with the cephalo-thorax. The tail bears a rudimentary fork between the prongs of which the anus opens. The swimming feet
have disappeared, so also has the eye and the spiral duct of the embryonic
frontal organ. The outer of the two divisions of the maxilliped have undergone the most important modification, in that they have become united at
their ends, where they form an organ from which an elongated rod (_/)
projects, and attaches the larva to the mouth or gills of its host. The
antennae and jaws have nearly acquired their adult form. The nervous
system consists of supra- and infra-cesophageal ganglia and two lateral
trunks given off from the latter. At this stage the males and females can
already be distinguished, not only by certain differences in the rudimentary generative organs, but also by the fact that the outer branch of the
maxillipeds is much longer in the female than in the male, and projects
beyond the head.
In the next ecdysis the adult condition is reached. The outer maxilli
1 Van Beneden (No. 506) in the genera investigated by him finds that the two
maxillipeds are really distinct pairs of appendages.
492 CIRRIPEDIA.
peds of the male (fig. 230 ,/>#*) separate again ; while in the female (fig.
230 D) they remain fused and develop a sucker. The male is only about
one-fifth the length of the female. In both sexes the abdomen is much
reduced.
In the genera Anchorella, Lernaeopoda, Brachiella and Hessia, Ed. van
BenecUn (No. 506) has shewn that the embryo, although it passes through
a crypto-Nauplius stage in the egg, is when hatched already in the Cyclops
stage.
Branchiura. The peculiar parasite Argulus, the affinities of which
with the Copepoda have been demonstrated by Claus (No. 511), is hatched
in a Cyclops stage, and has no Nauplius stage. At the time of hatching it
closely resembles the adult in general form. Its appendages are however
very nearly those of a typical larval Copepod. The body is composed of
a cephalo-thorax and free region behind this. The cephalo-thorax bears
on its under surface antennae (two pairs), mandibles, maxillipeds, and the
first pair of thoracic feet.
The first pair of antennae is three-jointed, but the basal joint bears a
hook. The second pair is biramous, the inner ramus terminating in a hook.
The mandible is palped, but the palp is completely separated from the
cutting blade 1 . The maxilla would, according to Claus, appear to be
absent.
The two typical divisions of the Copepod maxillipeds are present, viz. an
outer and anterior larger division, and an inner and posterior smaller one.
The first pair of thoracic feet, as is usual amongst Copepoda, is attached
to the cephalo-thorax. It has not the typical biramous Copepod character.
There are four free segments behind the cephalo-thorax, the last of which
ends in a fork. Three of them bear appendages, which are rudimentary in
this early larval stage. On the dorsal surface are present paired eyes as
well as an unpaired median eye.
Between the larval condition and that of the adult a number of ecdyses
intervene.
CIRRIPEDIA.
The larvae of all the Cirripedia, with one or two exceptions,
leave the egg in the Nauplius condition. The Nauplii differ
somewhat in the separate groups, and the post-nauplial stages
vary not inconsiderably.
It will be most convenient to treat successively the larval
1 It seems not impossible that the appendage regarded by Claus as the mandibular
palp may really represent the maxilla, which would otherwise seem to be absent.
This mode of interpretation would bring the appendages of Argulus into a much
closer agreement with those of the parasitic Copepoda. It does not seem incompatible
with the existence of the stylet-like maxillse detected by Claus in the adult.
CRUSTACEA. 493
history of the four sub-orders, viz. Thoracica, Abdominalia,
Apoda, and Rhizocephala.
Thoracica. The just hatched larvae at once leave the egg
lamellae of their parent. They pass out through an opening in
the mantle near the mouth, and during this passage the shell of
the parent is opened and the movements of the cirriform feet
cease.
The larval stages commence with a Nauplius 1 which, though
regarded by Claus as closely resembling the Copepod Nauplius
(figs. 231 and 232 A), certainly has very marked pecularities of
its own, and in some respects approaches the Phyllopod
Nauplius. It is in the youngest stage somewhat triangular in
form, and covered on the dorsal side by a very delicate and
hardly perceptible dorsal shield, which is prolonged laterally
into two very peculiar conical horns (fig. 231 Ik), which are the
most characteristic structures of the Cirriped Nauplius. They
are connected with a glandular mass, the secretion from which
passes out at their apex. Anteriorly the dorsal shield has the
same extension as the body, but posteriorly it projects slightly.
An unpaired eye is situated on the ventral surface of the
head, and immediately behind it there springs a more or less
considerable upper lip (Ib), which resembles the Phyllopod
labrum rather than that of the Copepoda. Both mouth and
anus are present, and the hind end of the body is slightly forked
in some forms, but ends in others, e.g. Lepas fascicularis, in an
elongated spine. The anterior of the three pairs of Nauplius
appendages (At*) is uniramous, and the two posterior (Af and
md) are biramous. From the protopodites of both the latter
spring strong hooks like those of the Copepod and Phyllopod
Nauplii. In some Nauplii, e.g. that of Balanus, the appendages
are at first not jointed, but in other Nauplii, e.g. that of Lepas
fascicularis, the jointing is well marked. In Lepas fascicularis
the earliest free Nauplius is enveloped in a larval skin, which is
thrown off after a few hours. The Nauplii of all the Thoracica
undergo a considerable number of moults before their appendages
increase in number or segmentation of the body appears. During
these moults they grow larger, and the posterior part of the
1 Alepas squalicola is stated by Koren and Danielssen to form an exception to
this rule, and to leave the egg with six pairs of appendages.
494
CIRRIPEDIA.
body the future thoracic and abdominal region grows relatively in length. There also appear close to the sides of the
unpaired eye two conical bodies, which correspond with the
frontal sense organs of the Phyllopods. During their growth
the different larvae undergo changes varying greatly in degree.
In Balanus the changes consist for the most part in the full
segmentation of the appendages and the growth and distinctness
FIG. 231. NAUPLIUS LARVA OF LEPAS FASCICULARIS VIEWED FROM THE SIDE.
oc. eye ; At. i. antenna of first pair ; At. 2. antenna of second pair ; md. mandible ;
Ib. labrum ; an. anus; me. mesenteron; d.sp. dorsal spine; c.sp. caudal spine;
Vp. ventral spine ; Ih. lateral horns.
of the dorsal shield, which forms a somewhat blunt triangular
plate, broadest in front, with the anterior horns very long, and
two short posterior spines. The tail also becomes produced into
a long spine.
In Lepas fascicularis the changes in appearance of the
Nauplius, owing to a great spinous development on its shield,
are very considerable ; and, together with its enormous size,
render it a very remarkable form. Dohrn (No. 520), who was
the first to describe it, named it Archizoaea gigas.
CRUSTACEA. 495
The dorsal shield of the Nauplius of Lepas fascicularis (fig. 231) becomes
somewhat hexagonal, and there springs from the middle of the dorsal surface
an enormously long spine (d,sp], like the dorsal spine of a Zoa^a. The hind
end of the shield is also produced into a long caudal spine (c.sfi] between
which and the dorsal spine are some feather-like processes. From its edge
there spring in addition to the primitive frontal horns three main pairs of
horns, one pair anterior, one lateral, and one posterior, and smaller ones in
addition. All these processes (with the exception of the dorsal and posterior
spines) are hollow and open at their extremities, and like the primitive
frontal horns contain the ducts of glands situated under the shield. On the
under surface of the larva is situated the unpaired eye (pc] on each side of
which spring the two-jointed frontal sense organs. Immediately behind
these is the enormous upper lip (lb] which covers the mouth 1 . At the sides
of the lip lie the three pairs of Nauplius appendages, which are very
characteristic but present no special peculiarities. Posteriorly the body is
produced into a long ventral spine-like process ( Vfi) homologous with that
of other more normal Nauplii. At the base of this process large moveable
paired spines appear at successive moults, six pairs being eventually formed.
These spines give to the region in which they are situated a segmented
appearance, and perhaps similar structures have given rise to the appearance of segmentation in Spence Bate's figures. The anus is situated on
the dorsal side of this ventral process, and between it and the caudal
spine of the shield above. The fact that the anus occupies this position
appears to indicate that the ventral process is homologous with the
caudal fork of the Copepoda, on the dorsal side of which the anus so
often opens 2 .
From the Nauplius condition the larvae pass at a single
moult into an entirely different condition known as the Cypris
stage. In preparation for this condition there appear, during
the last Nauplius moults, the rudiments of several fresh organs,
which are more or less developed in different types. In the
first place a compound eye is formed on each side of the
median eye. Secondly there appears behind the mandibles a
fourth pair of appendages the first pair of maxillae and
internal to these a pair of small prominences, which are perhaps
1 Willemoes Suhm (No. 530) states that the mouth is situated at the free end of the
upper lip, and that the oesophagus passes through it. From an examination of some
specimens of this Nauplius, for which I am indebted to Moseley, I am inclined to
think that this is a mistake, and that a groove on the surface of the upper lip has been
taken by Suhm for the oesophagus.
2 The enormous spinous development of the larva of Lepas fascicularis is probably
to be explained as a secondary protective adaptation, and has no genetic connection
with the somewhat similar spinous armature of the Zosea.
496" CIRRIPEDIA.
equivalent to the second pair of maxillae, and give rise to the
third pair of jaws in the adult (sometimes spoken of as the
lower lip).
Behind these appendages there are moreover formed the rudiments of six pairs of feet. Under the cuticle of the first pair of
antennae there may be seen just before the final moult the fourjointed antennae of the Cypris stage with the rudiment of a disc
on the second joint by which the larvae eventually become
attached.
By the free Cypris stage, into which the larva next passes, a
very complete metamorphosis has been effected. The median
and paired eyes are present as before, but the dorsal shield has
become a bivalve shell, the two valves of which are united along
their dorsal, anterior, and posterior margins. The two valves
are further kept in place by an adductor muscle situated close
below the mouth. Remains of the lateral horns still persist. The
anterior antennae have undergone the metamorphosis already
indicated. They are four-jointed, the two basal joints being
long, and the second provided with a suctorial disc, in the centre
of which is the opening of the duct of the so-called antennary or
cement gland, which is a granular mass lying on the ventral
side of the anterior region of the body. The gland arises
(Willemoes Suhm) during the Nauplius stage in the large upper
lip. The two distal joints of the antennae are short, and the
last of them is provided with olfactory hairs. The great upper
lip and second pair of antennae and mandibles have disappeared,
but a small papilla, forming the commencement of the adult
mandibles, is perhaps developed in the base of the Nauplius
mandibles. The first pair of maxillae have become small papillae
and the second pair probably remain. The six posterior pairs
of appendages have grown out as functional biramous swimming
feet, which can project beyond the shell and are used in the
locomotion of the larva. They are composed of two basal
joints, and two rami with swimming hairs, each two-jointed.
These feet resemble Copepod feet, and form the main ground
for the views of Claus and others that the Copepoda and
Cirripedia are closely related. They are regarded by Claus as
representing the five pairs of natatory feet of Copepoda, and the
generative appendages of the segment behind these. Between
CRUSTACEA.
497
the natatory feet are delicate chitinous lamellae, in the spaces
between which the cirriform feet of the adult become developed.
The ventral spinous process of the Nauplius stage is much reduced,
though usually three-jointed. It becomes completely aborted
after the larva is fixed.
In addition to the antennary gland there is present, near the
dorsal side of the body above the natatory feet, a peculiar paired
glandular mass, the origin of which has not been clearly made
out, but which is perhaps equivalent to the entomostracan shell
gland. It probably supplies the material for the shell in succeeding stages 1 .
The free Cypris stage is not of long duration ; and during it
the larva does not take food. It is succeeded by a stage known
as the pupa stage (fig. 232 B), in which the larva becomes fixed,
while underneath the larval skin the adult structures are developed. This stage fully deserves its name, since it is a quiescent stage during which no nutriment is taken. The attachment
takes place by the sucker of the antennae, and the cement gland
(/) supplies the cementing material for effecting it. A retrogressive metamorphosis of a large number of the organs sets in,
while at the same time the formation of new adult structures
is proceeded with. The eyes
become gradually lost, but the
Nauplius eye is retained,though
in a rudimentary state, and the
terminal joints of the antennae
with their olfactory hairs are
thrown off. The bivalve shell
is moulted about the same time
as the eyes, the skin below it
remaining as the mantle. The
caudal process becomes aborted. Underneath the natatory
FIG. 232. LARVAL FORMS OF THE
THORACICA. (From Huxley.)
A. Nauplius of Balanus balanoides.
(After Sp. Bate.) B. Pupa stage of Lepas
australis. (After Darwin.)
n. antennary apodemes ; /. cement
gland with duct to antenna.
1 There is considerable confusion about the shell gland and antennary gland. In
my account Willemoes Suhm has been followed. Claus however regards what I have
called the antennary gland as the shell gland, and states that it does not open into the
antennae till a later period. He does not clearly describe its opening, nor the organ
which I have called the shell gland.
B. II. 32
498 CIRRIPEDIA.
feet, and between the above-mentioned chitinous lamellae, the
cirriform feet are formed ; and on their completion the natatory
feet become thrown off and replaced by the permanent feet. In
the Lepadidae, in which the metamorphosis of the pupa stages
has been most fully studied, the anterior part of the body with
the antennae gradually grows out into an elongated stalk, into
which pass the ovaries, which are formed during the Cypris
stage. At the base of the stalk is the protuberant mouth, the
appendages of which soon attain a higher development than in
the Cypris stage. At the front part of it a large upper lip
becomes formed. Above the mantle and between it and the
shell there are formed in the Lepadidae the provisional valves of
the shell. These valves are chitinous, and have a fenestrated
structure, owing to the chitin being deposited round the margin
of the separate epidermis (hypodermis) cells. These valves in
the Lepadidae " prefigure in shape, size, and direction of growth,
the shelly valves to be formed under and around them" (Darwin,
No. 519, p. 129).
Whatever may be the number of valves in the adult the provisional
valves never exceed five, viz. the two scuta, the two terga and the carina.
They are relatively far smaller than the permanent valves and are therefore
separated by considerable membranous intervals. They are often preserved
for a long time on the permanent calcareous valves. In the Balanidce
the embryonic valves are membranous and do not overlap, but do not
present the peculiar fenestrated structure of the primordial valves of the
Lepadidae.
In connection with the moult of the pupa skin, and the
conversion of the pupa into the adult form, a remarkable change
in the position takes place. The pupa lies with the ventral side
parallel to and adjoining the surface of attachment, while the
long axis of the body of the young Cirriped is placed nearly at
right angles to the surface of attachment. This change is
connected with the ecdyses of the antennary apodemes (),
which leave a deep bay on the ventral surface behind the
peduncle. The chitinous skin of the Cirriped passes round
the head of this bay, but on the moult of the pupa skin
taking place becomes stretched out, owing to the posterior
part of the larva bending dorsalwards. It is this flexure which
causes the change in the position of the larva.
CRUSTACEA.
499
In addition to the remarkable external metamorphosis
undergone during the pupa stage, a series of hardly less considerable internal changes take place, such as the atrophy of
the muscles of the antennae, a change in the position of the
stomach, etc.
Abdominalia. In the Alcippidae the larva leaves the egg as a
Nauplius, and this stage is eventually followed by a pupa stage closely
resembling that of the Thoracica. There are six pairs of thoracic natatory
legs (Darwin, No. 519). Of these only the first and the last three are preserved in the adult, the first being bent forward in connection with the
mouth. The body moreover partially preserves its segmentation, and the
mantle does not secrete calcareous valves.
The very remarkable genus Cryptophialus, the development of which is
described by Darwin (No. 519) in his classical memoir, is without a free
Nauplius stage. The embryo is at first oval but soon acquires two anterior
processes, apparently the first pair of antennae, and a posterior prominence,
the abdomen. In a later stage the abdominal prominence disappears, and
the antennary processes, within which the true antennas are now visible, are
carried more towards the ventral
surface. The larva next passes into
the free Cypris stage, during which it
creeps about the mantle cavity of its
parent. It is enveloped in a bivalve
shell, and the antennae have the normal cirriped structure. There are no
other true appendages, but posteriorly
three pairs of bristles are attached to
a rudimentary abdomen. Paired compound eyes are present. During the
succeeding pupa stage the metamorphosis into the adult form takes place,
but this has not been followed out in
detail.
In Kochlorine, a form discovered
by Noll (No. 526) and closely related
to Cryptophialus, the larvae found
within the mantle represent apparently two larval stages, similar to
two of the larval stages described by
Darwin.
Rhizocephala. The Rhizocephala, as might have been antici
FIG. 233. STAGES IN THE DEVELOPMENT OF THE RHIZOCEPHALA. (From
Huxley, after Fritz Miiller.)
A. Nauplius of Sacculina purpurea.
B. Cypris stage of Lernseodiscus porcellanae. C. Adult of Peltogaster paguri.
II, III. IV. Two pairs of antennae
and mandibles; cp. carapace; a. anterior
end of body; b. generative aperture; c.
root-like processes.
pated from their close relationship to Anelasma squalicola amongst the
Thoracica, undergo a development differing much less from the type of the
Thoracica than that of Cryptophialus and Kochlorine.
322
5oo
OSTRACODA.
Sacculina leaves the egg as a Nauplius (fig. 233 A), which differs from
the ordinary type mainly (i) in the large development of an oval dorsal
shield (eft] which projects far beyond the edge of the body, but is provided
with the typical sternal horns, etc. ; and (2) in the absence of a mouth.
The Cypris and pupa stages of Sacculina and other Rhizocephala (fig. 233 B)
are closely similar to those of the Thoracica, but the paired eye is absent.
The attachment takes place in the usual way, but the subsequent metamorphosis leads to the loss of the thoracic feet and generally to retrogressive
changes.
OSTRACODA.
Our knowledge of the development of this remarkable group is entirely
due to the investigations of Claus.
Some forms of Cythere are viviparous, and in the marine form Cypridina
the embryo develops within the valves of the shell. Cypris attaches its
eggs to water plants. The larvae of Cypris are free, and their development
is somewhat complicated. The whole development is completed in nine
ecdyses, each of them accompanied by more or less important changes in
the constitution of the larva.
In the earliest free stage the larva has the characters of a true Nauplius
with three pairs of appendages (fig. 234 A). The Nauplius presents howB A
-A'
MX SM
FlG. 234. TWO STAGES IN THE DEVELOPMENT OF CYPRIS. (From ChlUS.)
A. Earliest (Nauplius) stage. B. Second stage.
A'. A". First and second pairs of antennae ; Md. mandibles ; OL. labrum ;
MX,', first pair of maxilla; /". first pair of feet.
ever one or two very marked secondary characters. In the first place it is
completely enveloped in a fully formed bivalve shell, differing in unessential
points from the shell of the adult. An adductor muscle (SM] for the shell
is present. Again the second and third appendages, though locomotive in
function are neither of them biramous, and the third one already contains
a rudiment of the future mandibular blade, and terminates in an anteriorly
directed hook-like bristle. The first pair of antenna? is moreover very
similar to the second and is used in progression. Neither of the pairs of
CRUSTACEA.
501
antennae become much modified in the subsequent metamorphosis. The
Nauplius has a single median eye, as in the adult Cypris, and a fully
developed alimentary tract.
The second stage (fig. 234 B), inaugurated by the first moult, is mainly
characterized by the appearance of two fresh pairs of appendages, viz. the
first pair of maxillae and the first pair of feet ; the second pair of maxillae
not being developed till later. The first pair appear as leaf-like curved
FIG. 235. STAGES IN THE DEVELOPMENT OF CYPRIS. (From Claus.)
A. Fourth stage. B. Fifth stage.
MX', first maxilla ; MX", and/', second maxilla ; /". first pair of feet ; L. liver.
plates (Mx'} more or less like Phyllopod appendages (Claus) though at this
stage without an exopodite. The first pair of feet (/"} terminates in a
curved claw and is used for adhering. The mandibles have by this stage
fully developed blades, and have practically attained their adult form, consisting of a powerful toothed blade and a four-jointed palp.
During the third and fourth stages the first pair of maxillae acquire
their pectinated gill plate (epipodite) and four blades ; and in the fourth
stage (fig. 235 A) the second pair of maxillae (Mx"} arises, as a pair of
curved plates, similar to the first pair of maxillae at their first appearance.
The forked tail is indicated during the fourth stage by two bristles. During
the fifth stage (fig. 235 B) the number of joints of the first pair of antennae
becomes increased, and the posterior maxillae develop a blade and become
502
PHYLOGENY OF THE CRUSTACEA.
four-jointed ambulatory appendages terminating in a hook. The caudal fork
becomes more distinct.
In the sixth stage (fig. 236) the second and hindermost pair of feet becomes formed (/"') and the maxillae of the second pair lose their ambulatory
function, and begin to be converted into definite masticatory appendages by
the reduced jointing of their palp, and the increase of their cutting blades.
By the seventh stage all the appendages have practically attained their
Fu
FIG. 236. SIXTH STAGE IN THE DEVELOPMENT OF CYPRIS. (From Claus.)
MX!, first maxilla ; Mx".f. second maxilla; /'. and/"', first and second pair oi
feet ; Fu. caudal fork ; L. liver ; S.D. shell gland.
permanent form ; the second pair of maxillae has acquired small branchial
plates, and the two following feet have become jointed. In the eighth and
ninth stages the generative organs attain their mature form.
The larva of Cythere at the time of birth has rudiments of all the limbs,
but the mandibular palp still functions as a limb, and the three feet (2nd
pair of maxillae and two following appendages) are very rudimentary.
The larvae of Cypridina are hatched in a condition which to all intents
and purposes resembles the adult.
Phylogeny of the Crustacea.
The classical work of Fritz Miiller (No. 452) on the phylogeny of the
Crustacea has given a great impetus to the study of their larval forms, and
the interpretations of these forms which he has offered have been the subject
of a very large amount of criticism and discussion. A great step forward
in this discussion has been recently made by Claus in his memoir (No. 448).
The most fundamental question concerns the meaning of the Nauplius.
Is the Nauplius the ancestral form of the Crustacea, as is believed by Fritz
Miiller and Claus, or are its peculiarities and constant occurrence due to
some other cause ? The most plausible explanation on the second hypothesis
CRUSTACEA. 503
would seem to be the following. The segments with their appendages of
Arthropoda and Annelida are normally formed from before backwards,
therefore every member of these two groups with more than three segments
must necessarily pass through a stage with only three segments, and the fact
that in a particular group this stage is often reached on the larva being
hatched is in itself no proof that the ancestor of the group had only three
segments with their appendages. This explanation appears to me, so far
as it goes, quite valid ; but though it relieves us from the necessity of
supposing that the primitive Crustacea had only three pairs of appendages,
it does not explain several other peculiarities of the Nauplius 1 . The more
important of these are the following.
1. That the mandibles have the form of biramous swimming feet and
are not provided with a cutting blade.
2. That the second pair of antennae are biramous swimming feet with a
hook used in mastication, and are innervated (?) from the subcesophageal
ganglion.
3. The absence of segmentation in the Nauplius body. An absence
which is the more striking in that before the Nauplius stage is fully reached
the body of the embryo is frequently divided into three segments, e.g.
Copepoda and Cirripedia
4. The absence of a heart.
5. The presence of a median single eye as the sole organ of vision.
Of these points the first, second, and fifth appear only to be capable of
being explained phylogenetically, while with reference to the absence of a
heart it appears very improbable that the ancestral Crustacea were without
a central organ of circulation. If the above positions are accepted the
conclusion would seem to follow that in a certain sense the Nauplius is
an ancestral form but that, while it no doubt had its three anterior pairs
of appendages similar to those of existing Nauplii, it may perhaps have
been provided with a segmented body behind provided with simple biramous
appendages. A heart and cephalo-thoracic shield may also have been
present, though the existence of the latter is perhaps doubtful. There was
no doubt a median single eye, but it is difficult to decide whether or no
paired compound eyes were also present. The tail ended in a fork between
the prongs of which the anus opened ; and the mouth was protected by a
large upper lip. In fact, it may very probably turn out that the most
primitive Crustacea more resembled an Apus larva at the moult immediately
before the appendages lose their Nauplius characters (fig. 208 B), or a
Cyclops larva just before the Cyclops stage (fig. 229), than the earliest
Nauplius of either of these forms.
If the Nauplius ancestor thus reconstructed is admitted to have existed,
the next question in the phylogeny of the Crustacea concerns the relations
of the various phyla to the Nauplius. Are the different phyla descended
from the Nauplius direct, or have they branched at a later period from
1 For the characters of Nauplius vide p. 460.
504 PHYLOGENY OF THE CRUSTACEA.
some central stem? It is perhaps hardly possible as yet to give a full and
satisfactory answer to this question, which requires to be dealt with for each
separate phylum ; but it may probably be safely maintained that the existing
Phyllopods are members of a group which was previously much larger, and
the most central of all the Crustacean groups; and which more nearly
retains in the characters of the second pair of antennae etc. the Nauplius
peculiarities. This view is shared both by Claus and Dohrn, and appears
to be in accordance with all the evidence we have both palaeontological and
morphological. Claus indeed carries this view still further, and believes
that the later Nauplius stages of the different Entomostracan groups and
the Malacostraca (Penaeus larva) exhibit undoubted Phyllopod affinities.
He therefore postulates the earlier existence of a Protophyllopod form, which
would correspond very closely with the Nauplius as reconstructed above,
from which he believes all the Crustacean groups to have diverged.
It is beyond the scope of this work to attempt to grapple with all the
difficulties which arise in connection with the origin and relationships of the
various phyla, but I confine myself to a few suggestions arising out of the
developmental histories recorded above.
Malacostraca. In attempting to reconstitute from the evidence in
our possession the ancestral history of the Malacostraca we may omit from
consideration the larval history of all those types which leave the egg in
nearly the adult form, and confine our attention to those types in which the
larval history is most completely preserved.
There are three forms which are of special value in this respect, viz.
Euphausia, Penaeus and Squilla. From the history of these which has
already been given it appears that in the case of the Decapoda four stages
(Claus) may be traced in the best preserved larval histories.
1. A Nauplius stage with the usual Nauplius characters.
2. A Protozoaea stage in which the maxillae and first pair of maxillipeds
are formed behind the Nauplius appendages ; but in which the tail is still
unsegmented. This stage is comparatively rarely preserved and usually not
very well marked.
3. A Zoaea stage the chief features of which have already been fully
characterised (vide p. 465). Three more or less distinct types of Zosea are
distinguished by Claus. (a) That of Penaeus, in which the appendages up
to the third pair of maxillipeds are formed, and the thorax and abdomen are
segmented, the former being however very short. The heart is oval, with
one pair of ostia. From this type the Zoaea forms of the other Decapoda
are believed by Claus to be derived, (b} That of Euphausia, with but one
pair of maxillipeds and those short and Phyllopod-like. The heart oval
with one pair of ostia. (c) That of Squilla, with an elongated manychambered heart, two pairs of maxillipeds and the abdominal appendages in
full activity.
4. A Mysis stage, which is only found in the macrurous Decapod
larvie.
The embryological questions requiring to be settled concern the value
CRUSTACEA. 50$
of the above stages. Do they represent stages in the actual evolution of
the present types, or have their characters been secondarily acquired in
larval life ?
With reference to the first stage this question has already been discussed,
and the conclusion arrived at, that the Nauplius does in a much modified
form represent an ancestral type. As to the fourth stage there can be no
doubt that it is also ancestral, considering that it is almost the repetition of
an actually existing form.
The second stage can clearly only be regarded as an embryonic preparation for the third ; and the great difficulty concerns the third stage.
The natural view is that this stage like the others has an ancestral value,
and this view was originally put forward by Fritz Miiller and has been
argued for also by Dohrn. On the other hand the opposite side has been
taken by Claus, who has dealt with the question very ably and at great
length, and has clearly shewn that some of Fritz Miiller's positions are
untenable. Though Claus' opinion is entitled to very great weight, an
answer can perhaps be given to some of his objections. The view adopted
in this section can best be explained by setting forth the chief points which
Claus urges against Fritz Miiller's view.
The primary question which needs to be settled is whether the Malacostraca have diverged very early from the Nauplius root, or later in the history
of the Crustacea from the Phyllopod stem. On this question Claus 1 brings
arguments, which appear to me very conclusive, to shew that the Malacostraca are derived from a late Protophyllopod type, and Claus' view on this
point is shared also by Dohrn. The Phyllopoda present so many characters
(not possessed by the Nauplius) in common with the Malacostraca or their
larval forms, that it is incredible that the whole of these should have
originated independently in the two groups. The more important of these
characters are the following.
1. The compound eyes, so often stalked in both groups.
2. The absence of a palp on the mandible, a very marked character of
the Zoasa as well as of the Phyllopoda.
3. The presence of a pair of frontal sense knobs.
4. The Phyllopod character of many of the appendages. Cf. first pair of
maxillipeds of the Euphausia Zosea.
1 Claus speaks of the various Crustacean phyla as having sprung from a Protophyllopod form, and it might be supposed that he considered that they all diverged from
the same form. It is clear however from the context that he regards the Protophyllopod type from which the Malacostraca originated as far more like existing Phyllopods than that from which the Entomostracan groups have sprung. It is not quite
easy to get a consistent view of his position on the question, since he states (p. 77) that
the Malacostraca and the Copepods diverged from a similar form, which is represented
in their respective developments by the Protozosea and earliest Cyclops stage. Yet if
I understand him rightly, he does not consider the Protozosea stage to be the Protophyllopod stage from which the Malacostraca have diverged, but states on p. 71 that
it was not an ancestral form at all.
506 PHYLOGENY OF THE CRUSTACEA.
5. The presence of gill pouches (epipodites) on many of the appendages 1 .
In addition to these points, to which others might be added, Claus
attempts to shew that Nebalia must be regarded as a type intermediate
between the Phyllopods and Malacostraca. This view seems fairly established, and if true is conclusive in favour of the Phyllopod origin of the
Malacostraca. If the Protophyllopod origin of the Malacostraca is admitted,
it seems clear that the ancestral forms of the Malacostraca must have developed their segments regularly from before backwards, and been provided
with nearly similar appendages on all the segments. This however is far
from the case in existing Malacostraca, and Fritz Miiller commences his
summary of the characters of the Zoaea in the following words 2 . "The
middle body with its appendages, those five pairs of feet to which these
animals owe their name, is either entirely wanting or scarcely indicated."
This he regards as an ancestral character of the Malacostraca, and is of
opinion that their thorax is to be regarded as a later acquirement than the
head or abdomen. Claus' answer on this point is that in the most primitive
Zoasas, viz. those already spoken of as types, the thoracic and abdominal
segments actually develop, in regular succession from before backwards,
and he therefore concludes that the late development of the thorax in the
majority of Zoaea forms is secondary and not an ancestral Phyllopod
peculiarity.
This is the main argument used by Claus against the Zosea having any
ancestral meaning. His view as to the meaning of the Zoaea may be
gathered from the following passage. After assuming that none of the
existing Zoaea types could have been adult animals, he says" Much more
"probably the process of alteration of the metamorphosis, which the Mala" costracan phylum underwent in the course of time and in conjunction
" with the divergence of the later Malacostracan groups, led secondarily
" to the three different Zoaea configurations to which probably later modifica" tions were added, as for instance in the young form of the Cumaceae. We
"might with the same justice conclude that adult Insects existed as cater" pillars or pupae as that the primitive form of the Malacostraca was a
" Protozoaea or Zoaea."
Granting Claus' two main positions, viz. that the Malacostraca are
derived from Protophyllopods, and that the segments were in the primary
ancestral forms developed from before backwards, it does not appear impossible that a secondary and later ancestral form may have existed with a
reduced thorax. This reduction may only have been partial, so that the
Zoaea ancestor would have had the following form. A large cephalo-thorax
and well-developed tail (?) with swimming appendages. The appendages up
to the second pair of maxillipeds fully developed, but the thorax very
1 Claus appears to consider it doubtful whether the Malacostracan gills can be
compared with the Phyllopod gill-pouches.
3 Facts for Darwin, p. 49.
CRUSTACEA. 507
imperfect and provided only with delicate foliaceous appendages not projecting beyond the edge of the cephalo-thoracic shield.
Another hypothesis for which there is perhaps still more to be said is
that there was a true ancestral Zoaea stage in which the thoracic appendages
were completely aborted. Claus maintains that the Zoaea form with
aborted thorax is only a larval form ; but he would probably admit that its
larval characters were acquired to enable the larva to swim better. If this
much be admitted it is not easy to see why an actual member of the
ancestral series of Crustacea should not have developed the Zoaea peculiarities when the mud-dwelling habits of the Phyllopod ancestors were
abandoned, and a swimming mode of life adopted. This view, which
involves the supposition that the five (or six including the third maxillipeds)
thoracic appendages were lost in the adult (for they may be supposed to
have been retained in the larva) for a series of generations, and reappeared
again in the adult condition, at a later period, may at first sight appear very
improbable, but there are, especially in the larval history of the Stomatopoda,
some actual facts which receive their most plausible explanation on this
hypothesis.
These facts consist in cases of the actual loss of appendages during
development, and their subsequent reappearance. The two most striking
cases are the following.
1. In the Erichthus form of the Squilla larva the appendages corresponding to the third pair of maxillipeds and first two pairs of ambulatory
appendages of the Decapoda are developed in the Protozosea stage, but
completely aborted in the Zoasa stage, and subsequently redeveloped.
2. In the case of the larva of Sergestes in the passage from the Acanthosoma (Mysis) stage to the Mastigopus stage the two hindermost thoracic
appendages become atrophied and redevelop again later.
Both of these cases clearly fit in very well with the view that there was an
actual period in the history of the Malacostraca in which the ancestors of
the present forms were without the appendages which are aborted and
redeveloped again in these larval forms. Claus' hypothesis affords no
explanation of these remarkable cases.
It is however always possible to maintain that the loss and reappearance
of the appendages in these cases may have no ancestral meaning ; and the
abortion of the first pair of maxillipeds and reduction of some of the other
appendages in the case of the Loricata is in favour of this explanation.
Similar examples of the abortion and reappearance of appendages, which
cannot be explained in the way attempted above, are afforded by the Mites
and also by the Insects, e.g. Bees.
On the other hand there is almost a conclusive indication that the loss
of the appendages in Sergestes has really the meaning assigned to it, in that
in the allied genius Leucifer the two appendages in question are actually
absent in the adult, so that the stage with these appendages absent is
permanently retained in an adult form. In the absence of the mandibular
palp in all the Zoaea forms, its actual atrophy in the Penaeus Zoasa, and its
508 PHYLOGENY OF THE CRUSTACEA.
universal reappearance in adult Malacostraca, are cases which tell in favour
of the above explanation. The mandibular palp is permanently absent in
Phyllopods, which clearly shews that its absence in the Zoaea stage is due to
the retention of an ancestral peculiarity, and that its reappearance in the
adult forms was a late occurrence in the Malacostracan history.
The chief obvious difficulty of this view is the redevelopment of the
thoracic feet after their disappearance for a certain number of generations.
The possibility of such an occurrence appears to me however clearly demonstrated by the case of the mandibular palp, which has undoubtedly been
reacquired by the Malacostraca, and by the case of the two last thoracic
appendages of Sergestes just mentioned. The above difficulty may be
diminished if we suppose that the larvae of the Zoaea ancestors always
developed the appendages in question. Such appendages might first only
partially atrophy in a particular Zoaea form and then gradually come to
be functional again ; so that, as a form with functional thoracic limbs
came to be developed out of the Zoaea, we should find in the larval history
of this form that the limbs were developed in the pre-zoaeal larval stages,
partially atrophied in the Zoaea stage, and redeveloped in the adult. From
this condition it would not be difficult to pass to a further one in which the
development of the thoracic limbs became deferred till after the Zoaea stage.
The general arguments in favour of a Zoaea ancestor with partially or
completely aborted thoracic appendages having actually existed in the past
appear to me very powerful. In all the Malacostracan groups in which
the larva leaves the egg in an imperfect form a true Zoaea stage is found.
That the forms of these Zoaeas should differ considerably is only what might
be expected, considering that they lead a free existence and are liable to
be acted upon by natural selection, and it is probable that none of those
at present existing closely resemble the ancestral form. The spines from
their carapace, which vary so much, were probably originally developed,
as suggested by Fritz Miiller, as a means of defence. The simplicity of
the heart so different from that of Phyllopods in most forms of Zoaea
is a difficulty, but the reduction in the length of the heart may very
probably be a secondary modification ; the primitive condition being retained
in the Squilla Zoaea. In any case this difficulty is not greater on the
hypothesis of the Zoaea being an ancestral form, than on that of its being a
purely larval one.
The points of agreement in the number and character of the appendages,
form of the abdomen, etc. between the various types of Zoaea appear to me
too striking to be explained in the manner attempted by Claus. It seems
improbable that a peculiarity of form acquired by the larva of some ancestral
Malacostracan should have been retained so permanently in so many groups l
1 A secondary larval form is less likely to be repeated in development than an
ancestral adult stage, because there is always a strong tendency for the former, which
is a secondarily intercalated link in the chain, to drop out by the occurrence of a
reversion to the original type of development.
CRUSTACEA. 509
more permanently indeed than undoubtedly ancestral forms like that of
Mysis and it would be still more remarkable that a Zoaea form should
have been two or more times independently developed.
There are perhaps not sufficient materials to reconstruct the characters of
the Zoaea ancestor, but it probably was provided with the anterior appendages up to the second pair of maxillipeds, and (?) with abdominal swimming feet. The heart may very likely have been many-chambered.
Whether gill pouches were present on the maxillipeds and abdominal feet
does not appear to me capable of being decided. The carapace and general
shape were probably the same as in existing Zoaeas. It must be left an open
question whether the six hindermost thoracic appendages were absent or
only very much reduced in size.
On the whole then it may be regarded as probable that the Malacostraca
are descended from Protophyllopod forms, in which, on the adoption of
swimming habits, six appendages of the middle region of the body were
reduced or aborted, and a Zoaea form acquired, and that subsequently the
lost appendages were redeveloped in the descendants of these forms, and
have finally become the most typical appendages of the group.
The relationship of the various Malacostracan groups is too difficult
a subject to be discussed here, but it seems to me most likely that in
addition to the groups with a Zoaea stage the Edriophthalmata and Cumaceae
are also post-zoaeal forms which have lost the Zoasa stage. Nebalia is
however very probably to be regarded as a prae-zoaeal form which has
survived to the present day ; and one might easily fancy that its eight thin
thoracic segments with their small Phyllopod-like feet might become nearly
aborted.
Copepoda. The Copepoda certainly appear to have diverged very
early from the main stem, as is shewn by their simple biramous feet and the
retention of the median eye as the sole organ of vision. It may be argued
that they have lost the eye by retrogressive changes, and in favour of this
view cases of the Pontellidae and of Argulus may be cited. It is however
more than doubtful whether the lateral eyes of the Pontellidae are related to
the compound Phyllopod eye, and the affinities of Argulus are still uncertain.
It would moreover be a great paradox if in a large group of Crustacea the
lateral eyes had been retained in a parasitic form only (Argulus), but lost in
all the free forms.
Cirripedia. The Cirripedia are believed by Claus to belong to the
same phylum as the Copepoda. This view does not appear to be completely
borne out by their larval history. The Nauplius differs very markedly from
that of the Copepoda, and this is still more true of the Cypris stage. The
Copepod-like appendages of this stage are chiefly relied upon to support the
above view, but this form of appendages was probably very primitive
and general, and the number (without taking into consideration the doubtful
case of Cryptophialus) does not correspond to that in Copepoda. On the
other hand the paired eyes and the bivalve shell form great difficulties in the
way of Claus' view. It is clear that the Cypris stage represents more or less
510
PHYLOGENY OF THE CRUSTACEA.
closely an ancestral form of the Cirripedia, and that both the large bivalve
shell and the compound eyes were ancestral characters. These characters
would seem incompatible with Copepod affinities, but point to the independent derivation of the Cirripedia from some early bivalve Phyllopod form.
Ostracoda. The independent origin of the Ostracoda from the main
Crustacean stem seems probable. Claus points out that the Ostracoda
present by no means a simple organisation, and concludes that they were
not descended from a form with a more complex organisation and a larger
number of appendages. Some simplifications have however undoubtedly
taken place, as the loss of the heart, and of the compound eyes in many
forms. These simplifications are probably to be explained (as is done by
Claus) as adaptations due to the small size of body and its enclosure in a
thick bivalve shell. Although Claus is strongly opposed to the view that
I)
FIG. 737. FIGURES ILLUSTRATING THE DEVELOPMENT OF ASTACUS. (From
Parker ; after Reichenbach.)
A. Section through part of the ovum during segmentation, n. nuclei ; w.y. white
yolk ; y.p. yolk pyramids ; c. central yolk mass.
B and C. Longitudinal sections during the gastrula stage, a. archenteron ;
b. blastopore ; ms. mesoblast ; ec. epiblast ; en. hypoblast distinguished from epiblast
by shading.
I '. Highly magnified view of the anterior lip of blastopore to shew the origin of
the primary mesoblast from the wall of the archenteron. p.ms. primary mesoblast ;
ec. epiblast ; en. hypoblast.
I Two hypoblast cells to shew the amoeba-like absorption of yolk spheres.
y. yolk ; . nucleus ; /. pseudopodial process.
F. Hypoblast cells giving rise endogenously to the secondary mesoblast (s.nts.).
tt. nuclei.
CRUSTACEA. 5 1
the number of the appendages has been reduced, yet the very fact of the
(in some respects) complex organisation of this group might seem to indicate
that it cannot have diverged from the Phyllopod stem at so early a stage as
(on Claus' view of the Nauplius) would seem to be implied by the very small
number of appendages which is characteristic of it, and it therefore appears
most probable that the present number may be smaller than that of the
ancestral forms.
The formation of the germinal layers.
The formation of the germinal layers has been more fully
studied in various Malacostraca, more especially in the Decapoda,
than in other groups.
Decapoda. To Bobretzky (No. 472) is due the credit of
having been the pioneer in this line of investigation ; and his
researches have been followed up and enlarged by Haeckel,
Reichenbach (No. 488), and Mayer (No. 482). The segmentation
is centrolecithal and regular (fig. 237 A). At its close the
blastoderm is formed of a single uniform layer of lens-shaped
cells enclosing a central sphere of yolk, in which as a rule all
trace of the division into columns, present during the earlier
stages of segmentation, has disappeared ; though in Palaemon
the columns remain for a long period distinct. The cells of the
blastoderm are at first uniform, but in Astacus, Eupagurus,
and most Decapoda, soon become more columnar for a small
area, and form a circular patch. The whole patch either
becomes at once invaginated (Eupagurus, Palaemon, fig. 239 A)
or else the edge of it is invaginated as a roughly speaking
circular groove deeper anteriorly than posteriorly, within which
the remainder of the patch forms a kind of central plug, which
does not become invaginated till a somewhat later period
(Astacus, fig. 237 B and C). After the invagination of the
above patch the remainder of the blastoderm cells form the
epiblast.
The invaginated sack appears to be the archenteron and its
mouth the blastopore. The mouth finally becomes closed 1 , and
the sack itself then forms the mesenteron.
In Astacus the archenteron gradually grows forwards, its
opening is at first wide, but becomes continuously narrowed
1 Bobretzky first stated that the invagination remained open, but subsequently
corrected himself. Zeit. /. Wiss. Zool., Bd. xxiv. p. 186.
512
FORMATION OF THE LAYERS.
and is finally obliterated. Very shortly after this occurrence
there is formed, slightly in front of the point where the last trace
of the blastopore was observable, a fresh epiblastic invagination,
which gives rise to the proctodaeum, and the opening of which
remains as the definite anus. The proctodaeum (fig. 238 A, kg)
is very soon placed in communication with the mesenteron (mg).
The stomodaeum (fg) is formed during the same stage as the
proctodaeum. It gives rise to the oesophagus and stomach.
The hypoblast cells which form the wall of the archenteron
grow with remarkable rapidity at the expense of the yolk ; the
spherules of which they absorb and digest in an amceba-like
fashion by means of their pseudopodia. They become longer
and longer, and finally, after absorbing the whole yolk, acquire
a form almost exactly similar to
that of the yolk pyramids during segmentation (fig. 238 B).
They enclose the cavity of the
mesenteron, and their nuclei
and protoplasm are situated externally. The cells of the mesenteron close to its junction
with the proctodaeum differ
from those elsewhere in being
nearly flat.
In Palaemon (Bobretzky)
the primitive invagination (fig.
239 A) has far smaller dimensions than in Astacus, and appears before the blastoderm
cells have separated from the
yolk pyramids. The cells which
are situated at the bottom of it
pass into the yolk, increase in
number, and absorb the whole
yolk, forming a solid mass of
hypoblast in which the outlines
of the individual cells would
seem at first not to be distinct.
FlG. 238. TWO LONGITUDINAL SECTIONS OF THE EMBRYO OF ASTACUS.
(From Parker ; after Bobretzky.)
A. Nauplius stage. B. Stage after
the hypoblast cells have absorbed the
food yolk. The ventral surface is turned
upwards, fg. stomodseum ; hg. proctodccum ; an. anus ; m. mouth ; mg. mesenteron ; abd. abdomen ; h. heart.
The blastopore in the mean
CRUSTACEA. 513
time becomes closed. Some of the nuclei now pass to the
periphery of the yolk mass ; the cells appertaining to them
gradually become distinct and assume a pyramidal form (fig.
239 B, hy\ the inner ends of the cells losing themselves in a
central mass of yolk, in the interior of which nuclei are at first
present but soon disappear. The mesenteron thus becomes
constituted of a layer of pyramidal cells which merge into
a central mass of yolk. Some of the hypoblast cells adjoining
the junction of the proctodaeum and mesenteron become
flattened, and in the neighbourhood of these cells a lumen
FlG. 239. TWO STAGES IN THE DEVELOPMENT OF PAL^MON SEEN IN SECTION.
(After Bobretzky.)
A. Gastrula stage.
B. Longitudinal section through a late stage, hy. hypoblast ; sg. supra-resophageal ganglion ; vg. ventral nerve cord ; hd. proctodseum ; st. stomodseum.
first appears. The stomodaeum and proctodaeum are formed as
in Astacus. Fig. 239 B shews the relative positions of the
proctodaeum, stomodaeum, and mesenteron. Although the
process of formation of the hypoblast and mesenteron is
essentially the same in Astacus and Palaemon, yet the differences
between these two forms are very interesting, in that the yolk is
external to the mesenteron in Astacus, but enclosed within it in
Palaemon. This difference in the position of the yolk is rendered
possible by the fact that the invaginated hypoblast cells in
Palaemon do not, at first, form a continuous layer enclosing a
central cavity, while they do so in Astacus.
The mesoblast appears to be formed of cells budded off
from the anterior wall of the archenteron (Astacus, fig. 237 D),
B. II. 33
514 FORMATION OF THE LAYERS.
or from its lateral walls generally (Palaemon). They make
their first appearance soon after the imagination of the hypoblast has commenced. The mesoblast cells are at first spherical,
and gradually spread, especially in an anterior direction, from
their point of origin.
According to Reichenbach there are formed in Astacus at the Nauplius
stage a number of peculiar cells which he speaks of as * secondary mesoblast
cells.' His account is not very clear or satisfactory, but it appears that they
originate (fig. 237 F) in the hypoblast cells by a kind of endogenous growth,
and though they have at first certain peculiar characters they soon become
indistinguishable from the remaining mesoblast cells.
Towards the end of the Nauplius period the secondary mesoblast cells
aggregate themselves into a rod close to the epiblast in the median ventral
line, and even bifurcate round the mouth and extend forwards to the
extremity of the procephalic lobes. This rod of cells very soon vanishes,
and the secondary mesoblast cells become indistinguishable from the
primary. Reichenbach believes, on not very clear evidence, that these cells
have to do with the formation of the blood.
General form of the body. The ventral thickening of epitlast
or ventral plate, continuous with the invaginated patch already
mentioned, forms the first indication of the embryo. It is at
first oval, but soon becomes elongated and extended anteriorly
into two lateral lobes the procephalic lobes. Its bilateral
symmetry is further indicated by a median longitudinal furrow.
The posterior end of the ventral plate next becomes raised into
a distinct lobe the abdomen which in Astacus at first lies in
front of the still open blastopore. This lobe rapidly grows in size,
and at its extremity is placed the narrow anal opening. It soon
forms a well-marked abdomen bent forwards over the region in
front (figs. 239 B, and 240 A and B). Its early development
as a distinct outgrowth causes it to be without yolk ; and so to
contrast very forcibly with the anterior thoracic and cephalic
regions of the body. In most cases this process corresponds to
the future abdomen, but in some cases (Loricata) it appears to
include part of the thorax. Before it has reached a considerable
development, three pairs of appendages spring from the region
of the head, viz. two pairs of antennae and the mandibles, and
inaugurate a so-called Nauplius stage (fig. 240 A). These three
appendages are formed nearly simultaneously, but the hindermost appears to become visible slightly before the two others
CRUSTACEA. 515
(Bobretzky). The mouth lies slightly behind the anterior pair
of antennae, but distinctly in front of the posterior pair. The
other appendages, the number of which at the time of hatching
varies greatly in the different Decapods (vide section on larval
development), sprout in succession from before backwards (fig.
240 B). The food yolk in the head and thoracic region
gradually becomes reduced in quantity with the growth of the
embryo, and by the time of hatching the disparity in size between
the thorax and abdomen has ceased to exist.
Isopoda. The early embryonic phases of the Isopoda have
been studied by means of sections by Bobretzky (No. 498) and
Bullar (No. 499) and have been found to present considerable
FlG. 240. TWO STAGES IN THE DEVELOPMENT OF
A. Nauplius stage.
B. Stage with eight pairs of appendages, op. eyes ; at 1 , and at*, first and second
antennae; md. mandibles; mx l , mx 2 . first and second maxillae; mxp*. third maxillipeds ; Ib. upper lip.
variations. When laid the egg is enclosed in a chorion, but
shortly after the commencement of segmentation (Ed. van
Beneden and Bullar) a second membrane appears, which is
probably of the nature of a larval membrane.
In all the forms the segmentation is followed by the
formation of a blastoderm, completely enclosing the yolk, and
thickened along an area which will become the ventral surface of
the embryo. In this area the blastoderm is formed of at least
two layers of cells an external columnar epiblast, and an
internal layer of scattered cells which form the mesoblast and
probably in part also the hypoblast (Oniscus, Bobretzky ; Cymothoa, Bullar).
332
516 FORMATION OF THE LAYERS.
In Asellus aquaticus there is a centrolecithal segmentation,
ending in the formation of a blastoderm, which appears first
on the ventral surface and subsequently extends to the dorsal.
In Oniscus murarius, and Cymothoa the segmentation is
partial [for its peculiarities and relationship vide p. 120] and a
disc, formed of a single layer of cells, appears at a pole of the
egg which corresponds to the future ventral surface (Bobretzky).
This layer gradually grows round the yolk partly by division of
its cells, though a formation of fresh cells from the yolk may
also take place. Before it has extended far round the yolk, the
central part of it becomes two or more layers deep, and the cells
of the deeper layers rapidly increase in number, and are destined
to give rise to the mesoblast and probably also to part or the
whole of the hypoblast. In Cymothoa this layer does not at
first undergo any important change, but in Oniscus it becomes
very thick, and its innermost cells (Bobretzky) become imbedded
in the yolk, which they rapidly absorb; and increasing in
number first of all form a layer in the periphery of the yolk, and
finally fill up the whole of the interior of the yolk (fig. 241 A),
absorbing it in the process.
It appears possible that these cells do not, as Bobretzky believes, originate from the blastoderm, but from nuclei in the yolk which have escaped
his observation. This mode of origin would be similar to that by which yolk
cells originate in the eggs of the Insecta, etc. If Bobretzky's account is
correct we must look to Palaemon, as he himself suggests, to find an explanation of the passage of the hypoblast cells into the yolk. The thickening of
the primitive germinal disc would, according to this view, be equivalent to
the invagination of the archenteron in Astacus, Palaemon, etc.
Whatever may be the origin of the cells in the yolk they no
doubt correspond to the hypoblast of other types. In Cymothoa
nothing similar to them has been met with, but the hypoblast
has a somewhat different origin ; being apparently formed from
some of the indifferent cells below the epiblast, which collect as
a solid mass on the ventral surface, and then divide into two
masses which become hollow and give rise to the liver caeca.
Their fate, as well as that of the hypoblast in Oniscus, is dealt
with in connection with the alimentary tract. The completion
of the enclosure of the yolk by the blastoderm takes place on
the dorsal surface. In all the Isopods which have been carefully
CRUSTACEA. 517
studied, there appears before any other organ a provisional
structure formed from the epiblast and known as the dorsal
organ. An account of it is given in connection with the development of the organs. The general external changes undergone by the larva in its development are as follows. The
ventral thickened area of the blastoderm (ventral plate) shapes
itself and girths nearly the whole circumference of the ovum in
Oniscus (fig. 241 A) but is relatively much shorter in Cymothoa.
Anteriorly it dilates into the two procephalic lobes. In
Cymothoa it next becomes segmented; and the anterior segments are formed nearly simultaneously, and those of the
abdomen somewhat later. At the same time a median depres
FlG. 241. TWO LONGITUDINAL SECTIONS THROUGH THE EMBRYO OF ONISCUS
MURARIUS. (After Bobretzky.)
st. stomodaeum ; pr. proctodseum ; hy. hypoblast formed of large nucleated cells
imbedded in the yolk ; m. mesoblast ; vg. ventral nerve cord ; sg. supra- oesophageal
ganglion ; li. liver ; do. dorsal organ ; zp. rudiment of masticatory apparatus ; ol. upper
lip.
sion appears dividing the blastoderm longitudinally into two
halves. The appendages are formed later than their segments,
and the whole of them are formed nearly simultaneously, with
the exception of the last thoracic, which does not appear till
comparatively late after the hatching of the embryo. The late
development of the seventh thoracic segment and appendage is
a feature common to the majority of the Isopoda (Fritz Miiller).
In Oniscus the limbs are formed in nearly the same way as in
Cymothoa, but in Asellus they do not arise quite simultaneously.
First of all, the two antennae and mandibles (the future palp)
appear, inaugurating a stage often spoken of as the Nauplius
stage, which is supposed to correspond with the free Nauplius
5l8 FORMATION OF THE LAYERS.
stage of Penaeus and Euphausia. At this stage a cuticle is shed
(Van Beneden) which remains as an envelope surrounding the
larva till the time of hatching. Similar cuticular envelopes are
formed in many Isopoda. Subsequently the appendages of the
thorax appear, and finally those of the abdomen. Later than
the appendages there arise behind the mouth two prominences
which resemble appendages, but give rise to a bilobed lower lip
(Dohrn).
In Asellus and Oniscus the ventral plate moulds itself to the
shape of the egg, and covers the greater part of the dorsal as
well as of the ventral side (fig. 241 A). As a result of this the
ventral surface of the embryo is throughout convex ; and in
Asellus a deep fold appears on the back of the embryo, so that
the embryo appears coiled up within the egg with its ventral
side outwards and its head and tail in contact. In Oniscus the
ventral surface is convex, but the dorsal surface is never bent in
as in Asellus. In Cymothoa the egg is very big and the
ventral plate does not extend nearly so far round to the dorsal
side as in Asellus, in consequence of which the ventral surface
is not nearly so convex as in other Isopoda. At the same time
the telson is early formed, and is bent forwards so as to lie
on the under side of the part of the blastoderm in front. In
having this ventral curvature of the telson Cymothoa forms
an exception amongst Isopods ; and in this respect is intermediate between the embryos of Asellus and those of the
Amphipoda.
Amphipoda. Amongst the Amphipoda the segmentation
is usually centrolecithal. In the case of Gammarus locusta
(Ed. van Beneden and Bessels, No. 503) it commences with
an unequal but total segmentation like that of the Frog (vide p.
97), and the separation of a central yolk mass is a late occurrence ; and it is noticeable that the part of the egg with the
small segments eventually becomes the ventral surface. In the
fresh-water species of Gammarus (G. pulex and fluviatilis) the
segmentation is more like that of Insects ; the blastoderm cells
being formed nearly simultaneously over a large part of the
surface of the egg.
Both forms of segmentation give rise to a blastoderm covering the whole egg, which soon becomes thickened on the ventral
CRUSTACEA. 519
surface. There is formed, as in the Isopoda, a larval membrane
at about the time when the blastoderm is completed. Very
soon after this the egg loses its spherical shape, and becomes
produced into a pointed extremity the future abdomen which
is immediately bent over the ventral surface of the part in front.
The ventral curvature of the hinder part of the embryo at so
early an age stands in marked contrast to the usual condition of
Isopod embryos, and is only approached in this group, so far as
is known, in the case of Cymothoa.
At the formation of the first larval membrane the blastoderm
cells separate themselves from it, except at one part on the
dorsal surface. The patch of cells adherent at this part gives rise
to a dorsal organ, comparable with that in Oniscus, connecting
the embryo and its first larval skin. A perforation appears in it
at a later period.
The segments and limbs of the Amphipoda are all formed
before the larva leaves the egg.
Cladocera. The segmentation (Grobben, No. 455) takes place on the
normal centrolecithal type, but is somewhat unequal. Before the close of
the segmentation there may be seen at the apex of the vegetative pole one
cell marked off from the remainder by its granular aspect. It gives rise
to the generative organs. One of the cells adjoining it gives rise to the
hypoblast, and the other cells which surround it form the commencement
of the mesoblast. The remaining cells of the ovum form the epiblast. By
a later stage the hypoblast cell is divided into thirty-two cells and the genital
cell into four, while the mesoblast forms a circle of twelve cells round the
genital mass.
The hypoblast soon becomes involuted ; the blastopore probably closes,
and the hypoblast forms a solid cord of cells which eventually becomes the
mesenteron. The stomodaeum is said to be formed at the point of closure
of the blastopore. The mesoblast passes inwards and forms a mass adjoining the hypoblast, and somewhat later the genital mass also becomes
covered by the epiblast. The proctodseum appears to be formed later than
the stomodasum.
The embryo as first shewn by Dohrn passes through a Nauplius stage
in the brood-pouch, but is hatched, except in the case of the winter eggs of
Leptodora, in a form closely resembling the adult.
Copepoda. Amongst the free Copepoda the segmentation and
formation of the layers have recently been investigated by Hoek (No. 512).
He finds that there is, in both the fresh-water and marine forms studied
by him, a centrolecithal segmentation similar to that of Palaemon and
Pagurus (vide p. 112), which might from the surface be supposed to be
520 FORMATION OF THE LAYERS.
complete and nearly regular. After the formation of the blastoderm an
invagination of some of its cells takes place and is completed in about a
quarter of an hour. The opening becomes closed. This invagination is
compared by Hoek to the invagination in Astacus, and is believed by him
to give rise to the mesenteron. Its point of closing corresponds with the
hind end of the embryo. On the ventral surface there appear two transverse furrows dividing the embryo into three segments, and a median
longitudinal furrow which does not extend to the front end of the foremost
segment. The three pairs of Nauplius appendages and upper lip become
subsequently formed as outgrowths from the sides of the ventral blastodermic thickening.
Amongst the parasitic Copepoda there are found two distinct types of
segmentation, analogous to those in the Isopoda. In the case of Condracanthus the segmentation is somewhat irregular, but on the type of Eupagurus, etc. (vide p. 112). In the other group (Anchorella, Clavella, Congericola, Caligus, Lerneopoda) the segmentation nearly resembles the ordinary
meroblastic type (vide p. 120), and is to be explained in the same manner as
in the cases of Oniscus and Cymothoa. The first blastodermic cells sometimes appear in a position corresponding with the head end of the embryo
(Anchorella), at other times at the hind end (Clavella), and sometimes in the
middle of the ventral surface. The dorsal surface of the yolk is always
the latest to be inclosed by the blastoderm cells. A larval cuticle similar
to that of the Isopoda is formed at the same time as the blastoderm. At
the sides of the ventral thickening of the blastoderm there grow out the
Nauplius appendages, of which only the first two appear in Anchorella.
In Anchorella and Lerneopoda the embryos are not hatched at the
Nauplius stage, but after the Nauplius appendages have been formed
a fresh cuticle the Nauplius cuticle is shed, and within it the embryo
develops till it reaches the so-called Cyclops stage (vide p. 490). The
embryo within the egg has its abdomen curved dorsalwards as amongst the
Isopoda.
Cinipedia. The segmentation of Balanus and Lepas commences by
the segregation of the constituents of the egg into a more protoplasmic
portion, and a portion formed mainly of food material. The former separates from the latter as a distinct segment, and then divides into two not
quite equal portions. The division of the protoplasmic part of the embryo
continues, and the resulting segments grow round the single yolk segment.
The point where they finally enclose it is situated on the ventral surface
(Lang) at about the position of the mouth (?).
After being enclosed by the protoplasmic cells the yolk divides, and gives
rise to a number of cells, which probably supply the material for the walls of
the mesenteron. The external layer of protoplasm forms the so-called
blastoderm, and soon (Arnold, Lang) becomes thickened on the dorsal
surface.
The embryo is next divided by two constrictions into three segments ;
and there are formed the three appendages corresponding to these, which are
CRUSTACEA. 52!
at first simple. The two posterior soon become biramous. The larva leaves
the egg before any further appendages become formed.
Comparative development of the organs.
Central nervous system. The ventral nerve cord of the
Crustacea develops as a thickening of the epiblast along the
median ventral line ; the differentiation of which commences in
front, and thence extends backwards. The ventral cord is at
first unsegmented. The supra-oesophageal ganglia originate as
thickenings of the epiblast of the procephalic lobes.
The details of the above processes are still in most cases very imperfectly known. The fullest account we have is that of Reichenbach (No. 488)
for Astacus. He finds that the supra- cesophageal ganglia and ventral cord
arise as a continuous formation, and not independently as would seem to be
the case in Chsetopoda. The supra-cesophageal ganglia are formed from the
procephalic lobes. The first trace of them is visible in the form of a pair of
pits, one on each side of the middle line. These pits become in the
Nauplius stage very deep, and their walls are then continued into two ridges
where the epiblast is several cells deep, which pass backwards one on each
side of the mouth. The walls of the pits are believed by Reichenbach to
give rise to the optic portions of the supra-cesophageal ganglia, and the
epiblastic ridges to the remainder of the ganglia and to the circum-cesophageal commissures. At a much later stage, when the ambulatory feet have
become formed, a median involution of epiblast in front of the mouth and
between the two epiblast ridges gives rise to a central part of the supracesophageal ganglia. Five elements are thus believed by Reichenbach to be
concerned in the formation of these ganglia, viz. two epiblast pits, two
epiblast ridges, and an involution of epiblast between the latter. It should
be noted however that the fate neither of the pair of pits, nor of the median
involution, appears to have been satisfactorily worked out. The two
epiblast ridges, which pass back from the supra-cesophageal ganglia on
each side of the mouth, are continued as a pair of thickenings of the epiblast
along the sides of a median ventral groove. This groove is deep in front
and shallows out posteriorly. The thickenings on the sides of this groove
no doubt give rise to the lateral halves of the ventral cord, and the cells of
the groove itself are believed by Reichenbach, but it appears to me without
sufficient evidence, to become invaginated also and to assist in forming the
ventral cord. When the ventral cord becomes separated from the epiblast
the two halves of it are united in the middle line, but it is markedly bilobed
in section.
In the Isopoda it would appear both from Bobretzky's and Bullar's
observations that the ventral nerve cord arises as an unpaired thickening of
the epiblast in which there is no trace of anything like a median involution.
After this thickening has become separated from the epiblast a slight
522 DEVELOPMENT OF ORGANS.
median furrow indicates its constitution out of two lateral cords. The
supra-oesophageal ganglia are stated to be developed quite simply as a pair
of thickenings of the procephalic lobes, but whether they are from the
first continuous with the ventral cord does not appear to have been determined.
The later stages in the differentiation of the ventral cord are,
so far as is known, very similar throughout the Crustacea. The
ventral cord is, as has been stated, at first unsegmented (fig. 241
A, vg\ but soon becomes divided by a series of constrictions into
as many ganglia as there are pairs of appendages or segments
(fig. 241 B, vg).
There appears either on the ventral side (Oniscus) or in the
centre (Astacus, Palaemon) of the two halves of each segment or
ganglion a space filled with finely punctuated material, which is
the commencement of the commissural portion of the cords.
The commissural tissue soon becomes continuous through the
length of the ventral cord, and is also prolonged into the supracesophageal ganglia.
After the formation of the commissural tissue the remaining
cells of the cord form the true ganglion cells. A gradual
separation of the ganglia next takes place, and the cells become
confined to the ganglia, which are finally only connected by a
double band of commissural tissue. The commissural tissue not
only gives rise to the longitudinal cords connecting the successive
ganglia, but also to the transverse commissures which unite the
two halves of the individual ganglia.
The ganglia usually, if not always, appear at first to correspond in number with the segments, and the smaller number so
often present in the adult is due to the coalescence of originally
distinct ganglia.
Organs of special sense. Comparatively little is known on
this head. The compound eyes are developed from the coalescence of two structures, both however epiblastic, viz. (i) part of
the superficial epiblast of the procephalic lobes ; (2) part of the
supra-cesophageal ganglia. The former gives rise to the corneal
lenses, the crystalline cones, and the pigment surrounding
them ; the latter to the rhabdoms and the cells which encircle
them. Between these two parts a mesoblastic pigment is interposed.
CRUSTACEA.
523
Of the development of the auditory and olfactory organs
almost nothing is known.
Dorsal organ. In a considerable number of the Malacostraca
and Branchiopoda a peculiar organ is developed from the epiblast
in the anterior dorsal region. This organ has been called the
dorsal organ. It appears to be of a glandular nature, and is
usually very large in the embryo or larva and disappears in the
adult ; but in some Branchiopoda it persists through life. In
most cases it is unpaired, but in some instances a paired organ
appears to take its place.
Various views as to its nature have been put forward. There
is but little doubt of its being glandular, and it is possible that it
is a provisional renal organ, though so far as I know concretions
have not yet been found in it.
Its development has been most fully studied in the Isopoda.
In Cymothoa (Bullar, No. 499) there appears on the dorsal surface, in the
region which afterwards becomes the first thoracic segment, an unpaired
linear thickening of the blastoderm. This soon becomes a circular patch,
the central part of which is invaginated so as to communicate
with the exterior by a narrow
opening only (fig. 242). It becomes at the same time attached
to the inner egg membrane. It
retains this condition till the close
of larval life.
In Oniscus (Dohrn, No. 500 ;
Bobretzky, No. 498) there appears
very early a dorsal patch of thickened cells. These cells become
attached at their edge to the
inner egg membrane and gradually separated from the embryo,
with which they finally only re- , FlG - W- DIAGRAMMATIC SECTION OF
. , ... CYMOTHOA SHEWING THE DORSAL ORGAN.
main in connection by a hollow (F rom Bullar.)
column of cells (fig. 241 A, do).
The original patch now gradually spreads over the inner egg membrane, and
forms a transverse saddle-shaped band of flattened cells which engirths the
embryo on all but the ventral side.
In the Amphipods the epiblast cells remain attached for a small area on
the dorsal surface to the first larval skin, when this is formed. This patch
of cells, often spoken of as a micropyle apparatus, forms a dorsal organ
equivalent to that in Oniscus. A perforation is formed in it at a later
524
DEVELOPMENT OF ORGANS.
period. A perhaps homologous structure is found in the embryos of Euphausia, Cuma, etc.
In many Branchiopoda a dorsal organ is found. Its development has
been studied by Grobben in Moina. It
persists in the adult
in Branchipus, Limnadia, Estherea, etc.
In the Copepoda
a dorsal organ is
sometimes found in
the embryo ; Grobben at any rate believes that he has
detected an organ of
this nature in the
embryo of Cyclops
serrulatus.
A paired organ
which appears to be
FIG. 243. DIAGRAMMATIC SECTION OF AN EMBRYO
OF ASELLUS AQUATICUS TO SHEW THE PAIRED DORSAL
ORGAN. (From Bullar ; after E. van Beneden.)
of the same nature
has been found in
Asellus and Mysis.
In Asellus (Rathke (No. 501), Dohrn (No. 500), Van Beneden (No. 497))
this organ originates as two cellular masses at the sides of the body just
behind the region of the procephalic lobes. Each of them becomes trifoliate
and bends towards the ventral surface. In each of their lobes a cavity
arises and finally the three cavities unite, forming a trilobed cavity open to
the yolk. This organ eventually becomes so large that it breaks through the
egg membranes and projects at the sides of the embryo (fig. 243\ Though
formed before the appendages it does not attain its full development till
considerably after the latter have become well established.
In Mysis it appears during the Nauplius stage as a pair of cavities lined
by columnar cells, which atrophy very early.
Various attempts have been made to identify organs in other Arthropod
embryos with the dorsal organ of the Crustacea, but the only organ at all
similar which has so far been described is one found in the embryo of Linguatula (vide Chapter XIX.), but there is no reason to think that this organ is
really homologous with the dorsal organ of the Crustacea.
The mesoblast. The mesoblast in the types so far investigated arises from the same cells as the hypoblast, and appears
as a somewhat irregular layer between the epiblast and the
hypoblast. It gives rise to the same parts as in other forms, but
it is remarkable that it does not, in most Decapods and Isopods
CRUSTACEA. 525
(and so far we do not know about other forms), become divided
into somites, at any rate with the same distinctness that is usual
in Annelids and Arthropods. Not only so, but there is at first
no marked division into a somatic and splanchnic layer with an
intervening body cavity. Some of the cells become differentiated
into the muscles of the body wall and limbs ; and other cells,
usually in the form of a very thin layer, into the muscles of the
alimentary tract. In the tail of Palcsmon Bobretzky noticed
that the cells about to form the muscles of the body were
imperfectly divided into cubical masses corresponding with the
segments ; which however, in the absence of a central cavity,
differed from typical mesoblastic somites. In Mysis Metschnikoff states that the mesoblast becomes broken up into distinct
somites. Further investigations on this subject are required.
The body cavity has the form of irregular blood sinuses amongst
the internal organs.
Heart. The origin and development of the heart and vascular system
are but very imperfectly known.
In Phyllopods (Branchipus) Claus (No. 454) has shewn that the heart is
formed by the coalescence of the lateral parts of the mesoblast of the ventral
plates. The chambers are formed successively as the segments to which
they belong are established, and the anterior chambers are in full activity
while the posterior are not yet formed.
In Astacus and Palaemon, Bobretzky finds that at the stage before the
heart definitely appears there may be seen a solid mass of mesoblast cells
in the position which it eventually occupies 1 ; and considers it probable that
the heart originates from this mass. At the time when the heart can first
be made out and before it has begun to beat, it has the form of an oval sack
with delicate walls separated from the mesenteron by a layer of splanchnic
mesoblast. Its cavity is filled with a peculiar plasma which also fills up the
various cavities in the mesoblast. Around it a pericardial sack is soon
formed, and the walls of the heart become greatly thickened. Four bands
pass off from the heart, two dorsalwards which become fixed to the
integument, and two ventralwards. There is also a median band of cells
connecting the heart with the dorsal integument. The main arteries arise
as direct prolongations of the heart. Dohrn's observations on Asellus
greatly strengthen the view that the heart originates from a solid mesoblastic mass, in that he was able to observe the hollowing out of the mass in
1 Reichenbach describes these cells, and states that there is a thickening of the
epiblast adjoining them. In one place he states that the heart arises from this thickening of epiblast, and in another that it arises from the mesoblast. An epiblastic origin
of the heart is extremely improbable.
526 DEVELOPMENT OF ORGANS.
the living embryo (cf. the development of the heart in Spiders). Some of the
central cells (nuclei, Dohrn) become blood corpuscles. The formation of
these is not, according to Dohrn, confined to the heart, but takes place in
situ in all the parts of the body (antennae, appendages, etc.). The corpuscles
are formed as free nuclei and are primarily derived from the yolk, which at
first freely communicates with the cavities of the appendages.
Alimentary tract. In Astacus the formation of the mesenteron by
invagination, and the absorption of the yolk by the hypoblast cells, have
already been described. On the absorption of the yolk the mesenteron has
the form of a sack, the walls of which are formed of immensely long cells
the yolk pyramids at the base of which the nucleus is placed (fig. 238 B).
This sack gives rise both to the portion of the alimentary canal between the
abdomen and the stomach and to the liver. The epithelial wall of both of
these parts is formed by the outermost portions of the pyramids with the
nuclei and protoplasm becoming separated off from the yolk as a layer of
flat epithelial cells. The yolk then breaks up and forms a mass of nutritive
material filling up the cavity of the mesenteron.
The differentiation both of the liver and alimentary tract proper first
takes place on the ventral side, and commences close to the point where the
proctodasum ends, and extends forward from this point. A layer of epithelial
cells is thus formed on the ventral side of the mesenteron which very soon
becomes raised into a series of longitudinal folds, one of which in the
middle line is very conspicuous. The median fold eventually, by uniting
with a corresponding fold on the dorsal side, gives rise to the true mesenteron ; while the lateral folds form parallel hepatic cylinders, which in front
are not constricted off from the alimentary tract. The lateral parts of the
dorsal side of the mesenteron similarly give rise to hepatic cylinders. The
yolk pyramids of the anterior part of the mesenteron, which projects
forwards as a pair of diverticula on each side to the level of the stomach, are
not converted into hepatic cylinders till after the larva is hatched.
The proctodasum very early opens into the mesenteron, but the stomodaeum remains closed till the differentiation of the mid-gut is nearly
completed. The proctodaeum gives rise to the abdominal part of the intestine, and the stomodaeum to the oesophagus and stomach. The commencement of the masticatory apparatus in the latter appears very early as a
dorsal thickening of the epithelium.
The primitive mesenteron in Palaemon differentiates itself into the
permanent mid-gut and liver in a manner generally similar to that in
Astacus, though the process is considerably less complicated. A distinct
layer of cells separates itself from the outer part of the yolk pyramids,
and gives rise to the glandular lining both of the mid-gut and of the liver.
The differentiation of this layer commences behind, and the mid-gut very
soon communicates freely with the proctodasum. The lateral parts of
the primitive mesenteron become constricted into four wings, two directed
forwards and two backwards ; these, after the yolk in them has become
absorbed, constitute the liver. The median part simply becomes the me
CRUSTACEA. 527
senteron. The stomachic end of the stomodaeum lies in contact with the
mesenteron close to the point where it is continued into the hepatic
diverticula, and, though the partition-wall between the two becomes early
very thin, a free communication is not established till the yolk has been
completely absorbed.
The alimentary tract in the Isopoda is mainly if not entirely formed
from the proctodaeum and stomodaeum, both of which arise before any other
part of the alimentary system as epiblastic invaginations, and gradually
grow inwards (fig. 244). In Oniscus the liver is formed as two discs
at the surface of the yolk on each side of the anterior part of the body.
Their walls are composed of cubical cells derived from the yolk cells, the
pr
s r " a qcaggaw. rt -j_ .-. f .i~T' : . -^a^Mi^ . - .. >va^^^
Vff
FlG. 244. TWO LONGITUDINAL SECTIONS THROUGH THE EMBRYO OF ONISCUS
MURARIUS. (After Bobretzky.)
st. stomodaeum ; pr. proctodseum ; hy. hypoblast formed of large nucleated cells
imbedded in yolk ; m. mesoblast ; vg. ventral nerve cord ; jr^. supra- oesophageal ganglion ; li. liver; do. dorsal organ; zp. rudiment of masticatory apparatus.
origin of which was spoken of on p. 516. These two discs gradually take
the form of sacks (fig. 244 B, li.) freely open on their inner side to the
yolk. As these sacks continue to grow the stomodaeum and proctodaeum
do not remain passive. The stomodaeum, which gives rise to the oesophagus
and stomach of the adult, soon exhibits a posterior dilatation destined to
become the stomach, on the dorsal wall of which a well-marked prominence
the earliest trace of the future armature is soon formed (fig. 244 B,
xp}. The proctodaeum (pr) grows with much greater rapidity than the
stomodaeum, and its end adjoining the yolk becomes extremely thin or even
broken through. In the earliest stages it was surrounded by the yolk cells,
but in its later growth the yolk cells become gradually reduced in number
and appear to recede before it so much so that one is led to conclude
that the later growth of the proctodaeum takes place at the expense of the
yolk cells.
The liver sacks become filled with a granular material without a trace
of cells ; their posterior wall is continuous with the yolk cells, and their
anterior lies close behind the stomach. The proctodaeum continually
grows forwards till it approaches close to the stomodaeum, and the two
528 DEVELOPMENT OF ORGANS.
liver sacks, now united into one at their base, become directly continuous
with the proctodaeum. By the stage when this junction is effected the yolk
cells have completely disappeared. It seems then that in Oniscus the yolk
cells (hypoblast) are mainly employed in giving rise to the walls of the
liver ; but that they probably also supply the material for the later growth
of the apparent proctodaeum. It becomes therefore necessary to conclude
that the latter, which might seem, together with the stomodasum, to form
the whole alimentary tract, does in reality correspond to the proctodaeum
and mesenteron together, though the digestive fluids are no doubt mainly
secreted not in the mesenteron but in the hepatic diverticula. The proctodaeum and stomodaeum at first meet each other without communicating, but
before long the partition between the two is broken through.
In Cymothoa (Bullar, No. 499) the proctodaeum and stomodaeum
develop in the same manner as in Oniscus, but the hypoblast has quite
a different form. The main mass of the yolk, which is much greater than
in Oniscus, is not contained in definite yolk cells, but the hypoblast is
represented by (i) two solid masses of cells, derived apparently from the
inner layer of blastoderm cells, which give rise to the liver ; and (2) by a
membrane enclosing the yolk in which nuclei are present.
The two hepatic masses lie on the surface of the yolk, and each of them
becomes divided into three short caecal tubes freely open to the yolk.
The stomodaeum soon reaches its full length, but the proctodaeum grows
forwards above the yolk till it meets the stomodaeum. By the time this
takes place the liver caeca have grown into three large tubes filled with
fluid, and provided with a muscular wall. They now lie above the yolk,
and no longer communicate directly with the cavity of the yolk sack,
but open together with the yolk sack into the point of junction of the
proctodaeum and stomodaeum. The yolk sack of Cymothoa no doubt
represents part of the mesenteron, but there is no evidence in favour of
any part of the apparent proctodaeum representing it also, though it is
quite possible that it may do so. The relations of the yolk sack and hepatic
diverticula in Cymothoa appear to hold good for Asellus and probably for
most Isopoda.
The differences between the Decapods and Isopods in the development
of the mesenteron are not inconsiderable, but they are probably to be
explained by the relatively larger amount of food yolk in the latter forms.
The solid yolk in the Isopods on this view represents the primitive mesenteron of Decapods after the yolk has been absorbed by the hypoblast cells.
Starting from this standpoint we find that in both groups the lateral parts of
the mesenteron become the liver. In Decapods the middle part becomes
directly converted into the mid-gut, the differentiation of it commencing
behind and proceeding forwards. In the Isopods, owing to the mesenteron
not having a distinct cavity, the differentiation of it, which proceeds forwards
as in Decapods, appears simply like a prolongation forwards of the proctoda?um, the cells for the prolongation being probably supplied from the yolk.
In Cymothoa the food yolk is so bulky that a special yolk sack is developed
CRUSTACEA.
529
for its retention, which is not completely absorbed till some time after the
alimentary canal has the form of a continuous tube. The walls of this yolk
sack are morphologically a specially developed part of the mesenteron.
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(461) G. O. Sars. " Om en dimorph Udvikling samt Generationsvexel hos
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(464) E. Metschnikoff. Development of Nebalia (Russian), 1868.
B. II. 34
530 BIBLIOGRAPHY.
Schizopoda.
(465) E. van Beneden, " Recherches sur 1'Embryogenie des Crustaces. n.
DeVeloppement des Mysis." Bullet, de rAcadtmie roy. de Belgique, second series,
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(46G) C. Glaus. " Ueber einige Schizopoden u. niedere Malakostraken." Zett.
f. wiss. Zoologie, Bd. XII I., 1863.
(467) A. Dohrn. " Untersuchungen Ub. Bau u. Entwicklung d. Arthropoden."
Zeit.f. wiss. Zool.y Bd. XXL, 1871, .p. 375. Peneus zoaea (larva of Euphausia).
(468) E. Metschnikoff. " Ueber ein Larvenstadium von Euphausia." Zeit.
fiir wiss. Zool., Bd. xix., 1869.
(469) E. Metschnikoff. " Ueber den Naupliuszustand von Euphausia. " Zeit.
fiir wiss. Zool., Bd. XXI., 1871.
Decapoda.
(470) S pence Bate. "On the development of Decapod Crustacea." Phil.
Trans., 1858.
(471) Spence Bate. " On the development of Pagurus." Ann. and Mag. Nat.
History, Series 4, Vol. II., 1868.
(472) N. Bobretzky. Development of Astacus and Palamon. Kiew, 1873.
(Russian.)
(473) C. Glaus. "Zur Kenntniss d. Malakostrakenlarven. " Wiirzb. naturw.
Zeitschrift, 1861.
(474) R. Q. Couch. "On the Metamorphosis of the Decapod Crustaceans."
Report Cornwall Polyt. Society. 1848.
(475) Du Cane. "On the Metamorphosis of Crustacea." Ann. and Mag. of
Nat. History, 1839.
(476) Walter Faxon. " On the development of Palsemonetes vulgaris." Bull,
of the Mus. of Camp. Anat. Harvard, Cambridge, Mass., Vol. v., 1879.
(477) A. Dohrn. " Untersuchungen lib. Bau u. Entwicklung d. Arthropoden."
" Zur Entwicklungsgeschichte der Panzerkrebse. Scyllarus Palinurus." Zeit. f.
wiss. Zool., Bd. xx., 1870.
(478) A. Dohrn. "Untersuchungen lib. Bau u. Entwicklung d. Arthropoden.
Erster Beitrag z. Kenntniss d. Malacostraken u. ihrer Larven Amphion Reynaudi,
Lophogaster, Portunus, Porcellanus, Elaphocaris. " Zeit. f. wiss. Zool., Bd. xx.,
1870.
(479) A. Dohrn. "Untersuchungen lib. Bau u. Entwicklung d. Arthropoden.
Zweiter Beitrag, etc." Zeit.f. wiss. Zool., Bd. xxi., 1871.
(480) N. Joly. " Sur la Caridina Desmarestii." Ann. Scien. Nat., Tom. xix.,
1843.
(481) Lereboullet. " Recherches d . 1'embryologie comparee sur le developpement
du Brochet, de la Perche et de 1'Ecrevisse." Mem. Savans ktrang. Paris, Vol. xvn.,
1862.
(482) P. Mayer. "Zur Entwicklungsgeschichte d. Dekapoden." Jenaische
Zeitschrift, Vol. XI., 1877.
(483) F r i t z M u 1 1 e r. " Die Verwandlung der Porcellana." Archivf. Natnrgeschichte, 1862.
CRUSTACEA. 531
(484) Fritz Muller. " Die Verwandlungen d. Garneelen," Archiv f. Naturgesch., Tom. xxix.
(485) Fritz Muller. " Ueber die Naupliusbrut d. Garneelen." Zeit f. wiss.
Zool., Bd. xxx., 1878.
(486) T. J. Parker. "An account of Reichenbach's researches on the early
development of the Fresh-water Crayfish." Quart. J. of M. Science, Vol. xvin.,
1878.
(487) H. Rathke. Ueber die Bildung u. Entivicklung d. Flusskrebses. Leipzig, 1829.
(488) H. Reichenbach. " Die Embryoanlage u. erste Entwicklung d. Flusskrebses." Zeit.f. wiss. Zool., Vol. xxix., 1877.
(489) F. Richters. " Ein Beitrag zur Entwicklungsgeschichte d. Loricaten."
Zeit.f. wiss. Zool., Bd. xxiil., 1873.
(490) G. O. Sars. " Om Hummers posiembryonale Udvikling. " Vidensk Selsk.
Fork. Christiania, 1874.
(491) Sidney J. Smith. " The early stages of the American Lobster. " Trans,
of the Connecticut Acad. of Arts and Sciences, Vol. n., Part 2, 1873.
(492) R. v. Willemoes Suhm. " Preliminary note on the development of some
pelagic Decapoda." Proc. of Royal Society, 1876.
Stomatopoda.
(493) W. K. Brooks. " On the larval stages of Squilla empusa." Chesapeake
Zoological Laboratory, Scientific results of the Session of 1878. Baltimore, 1879
(494) C. Claus. "Die Metamorphose der Squilliden." Abhand. der kbnigl.
Gesell. der Wiss. zu Gbttingen, 1871.
(495) Fr. Muller. " Bruchstuck a. der Entwicklungsgeschichte d. Maulfusser I.
und II." Archiv f. Naturgeschichte, Vol. xxvin., 1862, and Vol. xxix., 1863.
Cumacea.
(496) A. Dohrn. " Ueber den Bau u. Entwicklung d. Cumaceen." Jenaische
Zeitschrift, Vol. v., 1870.
Isopoda.
(497) Ed. van Beneden. " Recherches sur 1'Embryogenie des Crustaces. I.
Asellus aquaticus." Bull, de FAcad. roy Belgique, 2me serie, Tom. xxvni., No. 7,
1869.
(498) N. Bobretzky. " Zur Embryologie des Oniscus murarius." Zeit. fur
wiss. Zool., Bd. xxiv., 1874.
(499) J. F. Bullar. "On the development of the parasitic Isopoda." Phil.
Trans., Part II., 1878.
(500) A. Dohrn. " Die embryonale Entwicklung des Asellus aquaticus." Zeit.
f. wiss. Zool., Vol. xvn., 1867.
(501) H. Rathke. Untersuchungen iiber die Bildung tmd Entwicklung der
Wasser-Assel. Leipzig, 1832.
(502) H. Rathke. Zur Morphologic. Reisebemerkungen aus Taurien. Riga u.
Leipzig, 1837. (Bopyrus, Idothea, Ligia, lanira.)
342
532 BIBLIOGRAPHY.
A mphipoda.
(503) Ed. van Beneden and E. Bessels. "M&noire sur la formation du
blastoderme chez les Amphipodes, les Lerneens et les Cope"podes." Classe des Sciences
deTAcad. roy. de Belgique, Vol. xxxiv., 1868.
(504) De la Valletta St George. " Studien iiber die Entwicklung der Amphipoden." Abhand. d. naturfor. Gesell. zu Halle, Bd. v., 1860.
Copepoda.
(505) E. van Beneden and E. Bessels. " Me*moire sur la formation du blastoderme chez les Amphipodes, les Lerndens et Copepodes." Classe des Sciences de
FAcad. roy. de Belgique, Vol. xxxiv., 1868.
(506) E. van Beneden. " Recherches sur 1'Embryogenie des Crustaces iv. Anchorella, Lerneopoda, Branchiella, Hessia." Bull, de FAcad. roy. de Belgique, 2me
serie, T. xxix., 1870.
(507) C. Claus. Zur Anatomie u. Entwicklungsgeschichte d. Copepoden.
(508) C. Claus. " Untersuchungen Uber die Organisation u. Verwandschaft d.
Copepoden." Wiirzburger naturwiss. Zeitschrift, Bd. III., 1862.
(509) C. Claus. " Ueber den Bau u. d. Entwicklung von Achtheres percarum."
Zeit.f. wiss. Zool., Bd. XL, 1862.
(510) C. Claus. Die freilebenden Copepoden mit besonderer Berucksichtigung der
Fauna Deutschlands, des Nordsee u. des Mittelmeeres. Leipzig, 1863.
(511) C. Claus. " Ueber d. Entwicklung, Organisation u. systematische Stellung
d. Argulidse." Zeit.f. wiss. Zool., Bd. xxv., 1875.
(512) P. P. C. Hoek. " Zur Entwicklungsgeschichte d. Entomostracen." Niederldndisches Archiv, Vol. IV., 1877.
(513) N o r d m a n n. Mikrographische Beitrdge zur Naturgeschichte der ivirbellosen
l^hiere. Zweites Heft. 1832.
(514) Salensky. " Sphseronella Leuckartii." Archivf. Naturgeschichte, 1868.
(515) F. Vejdovsky. "Untersuchungen Ub. d. Anat. u. Metamorph. v. Tracheliastes polycolpus." Zeit.f. wiss. Zool., Vol. xxix., 1877.
Cirripedia.
(516) C. Spence Bate. "On the development of the Cirripedia." Annals
and Mag. of Natur. History. Second Series, Vin., 1851.
(517) E. van Beneden. " DeVeloppement des Sacculines." Bull, de I" Acad.
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(518) C. Claus. Die Cypris-dhnliche Larve der Cifripedien. Marburg, 1869.
(519) Ch. Darwin. A monograph of the sub-class Cirripedia, i Vols., Ray
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(520) A. Dohrn. ' Untersuchungen iiber Bau u. Entwicklung d. Arthropoden
ix. Eine neue Naupliusform (Archizoea gigas)." Zeit. f. wiss. Zool., Bd. xx.,
1870.
(521) P. P. C. Hoek. "Zur Entwicklungsgeschichte der Entomostraken i.
Kinbryologie von Balanus." Niederldndisches Archiv fur Zoologie, Vol. III., 1876 7.
(522) R. Kossmann. "Suctoria u. Lepadidoc." Arbeiten a. d. zool.-zoot. Instituted. Univer. Wiirz., Vol. I., 1873.
CRUSTACEA. 533
(523) Aug. Krohn. " Beobachtungen iiber die Entwicklung der Cirripedien."
Wiegmanris Archiv fur Naturgesch., xxvi., 1860.
(524) E. Metschnikoff. Sitzungsberichte d. Versammlung deutscher Naturforscher zu Hannover, 1865. (Balanus balanoides.)
(525) Fritz Muller. "Die Rhizocephalen." Archiv f. Naturgeschichte,
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Zool., Bd. xxv., 1875.
(527) A. Pagenstecher. " Beitrage zur Anatomic und Entwicklungsgeschichte
von Lepas pectinata." Zeit.f. wiss. ZooL, Vol. xni., 1863.
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Memoir IV. On the Cirripedes or Barnacles. 8vo. Cork, 1830.
(529) J. V. Thompson. " Discovery of the Metamorphosis in the second type
of the Cirripedes, viz. the Lepades completing the natural history of these singular
animals, and confirming their affinity with the Crustacea." Phil. Trans. 1835. Part
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(530) R. von Willemoes Suhm. "On the development of Lepas fascicularis."
Phil. Trans., Vol. 166, 1876.
Ostracoda.
(531) C. Glaus. " Zur naheren Kenntniss der Jugendformen von Cypris ovum."
Zeit.f. wiss. ZooL, Bd. xv., 1865.
(532) C. Glaus. "Beitrage zur Kenntniss d. Ostracoden. Entwicklungsgeschichte von Cypris ovum." Schriften d. Gesell. zur Befdrderung d. gesamm. Naturwiss. zu Marburg, Vol. IX., 1868.
==CHAPTER XIX. PCECILOPODA, PYCNOGONIDA, TARDIGRADA, AND LINGUATULIDA; AND COMPARATIVE SUMMARY OF ARTHROPODAN DEVELOPMENT==
THE groups dealt with in the present Chapter undoubtedly
belong to the Arthropoda. They are not closely related, and in
the case of each group it is still uncertain with which of the
main phyla they should be united. It is possible that they may
all be offshoots from the Arachnidan phylum.
PCECILOPODA.
The development of Limulus has been studied by Dohrn (No. 533) and
Packard (No. 534). The ova are laid in the sand near the spring-tide
marks. They are enveloped in a thick chorion formed of several layers ;
and (during the later stages of development at any rate) there is a membrane within the chorion which exhibits clear indications of cell outlines 1 .
There is a centrolecithal segmentation, which ends in the formation of
a blastoderm enclosing a central yolk mass. A ventral plate is then
formed, which is thicker in the region where the abdomen is eventually
developed. Six segments soon become faintly indicated in the cephalothoracic region, the ends of which grow out into prominent appendages
(fig. 245 A) ; of these there are six pairs, which increase in size from before
backwards. A stomodaeum (m) is by this time established and is placed well
in front of the foremost pair of appendages'*-.
In the course of the next few days the two first appendages of the
abdominal region become formed (vide fig. 245 C shewing those abdominal
appendages at a later stage), and have a very different shape and direction
to those of the cephalothorax. The appendages of the latter become
1 The nature of the inner membrane is obscure. It is believed by Packard to be
moulted after the formation of the limbs, and to be equivalent to the amnion of Insects,
while by Dohrn it is regarded as a product of the follicle cells.
2 Dohrn finds at first only five appendages, but thinks that the sixth (the anterior
one) may have been present but invisible.
PCECILOPODA.
535
flexed in the middle in such a way that their ends become directed towards
the median line (fig. 245 B). The body of the embryo (fig. 245 B) is
now distinctly divided into two regions the cephalothoracic in front, and
the abdominal behind, both divided into segments.
FIG. 245. THREE STAGES IN THE DEVELOPMENT OF LIMULUS POLYPHEMUS.
(Somewhat modified from Packard.)
A. Embryo in which the thoracic limbs and mouth have become developed on
the ventral plate. The outer line represents what Packard believes to be the amnion.
B. Later embryo from the ventral surface.
C. Later embryo, just before the splitting of the chorion from the side. The full
number of segments of the abdomen, and three abdominal appendages, have become
established ; m. mouth ; I IX. appendages.
Round the edge of the ventral plate there is a distinct ridge the
rudiment of the cephalothoracic shield.
With the further growth of the embryo the chorion becomes split
and cast off, the embryo being left enclosed within the inner membrane.
The embryo has a decided ventral flexure, and the abdominal region
grows greatly and forms a kind of cap at the hinder end, while its
vaulted dorsal side becomes divided into segments (fig. 245 C). Of these
there are according to Dohrn seven, but according to Packard nine, of
which the last forms the rudiment of the caudal spine.
In the thoracic region the nervous system is by this stage formed as
a ganglionated cord (Dohrn), with no resemblance to the peculiar cesophageal ring of the adult. The mouth is stated by Dohrn to lie between the
second pair of limbs, so that, if the descriptions we have are correct, it must
have by this stage changed its position with reference to the appendages.
Between the thorax and abdomen two papillae have arisen which form the
536
PCEC1LOPODA.
so-called lower lip of the adult, but from their position and late development
they can hardly be regarded as segmental appendages. In the course of
further changes all the parts become more distinct, while the membrane in
which the larva is placed becomes enormously distended (fig. 246 A). The
rudiments of the compound eyes are formed on the third (Packard) or fourth
(Dohrn) segment of the cephalothorax, and the simple eyes near the median
line in front. The rudiments of the inner process of the chelae of the cephalothoracic appendages arise as buds. The abdominal appendages become
more plate-like, and the rudiments of a third pair appear behind the two
already present. The heart appears on the dorsal surface.
An ecdysis now takes place, and in the stage following the limbs have
approached far more closely to their adult state (fig. 246 A). The
cephalothoracic appendages become fully jointed ; the two anterior abdominal appendages (vn.) have approached, and begin to resemble the oper
ce.
VIII
FlO. 246. TWO STAGES IN THE DEVELOPMENT OF LlMULUS POLYPHEMUS.
(After Dohrn.)
A. An advanced embryo enveloped in the distended inner membrane shortly
before hatching ; from the ventral side.
B. A later embryo at the Trilobite stage, from the dorsal side.
I., vii., VIII. First, seventh, and eight appendages.
cs. caudal spine ; se. simple eye ; ce. compound eye.
culum of the adult, and on the second pair is formed a small inner ramus.
The segmentation of the now vaulted cephalothorax becomes less obvious,
though still indicated by the arrangement of the yolk masses which form
the future hepatic diverticula.
Shortly after this stage the embryo is hatched, and at about the time of
hatching acquires a form (fig. 246 B) in which it bears, as pointed out by
Dohrn and Packard, the most striking resemblance to a Trilobite.
Viewed from the dorsal surface (fig. 246 B) it is divided into two
distinct regions, the cephalothoracic in front and the abdominal behind.
The cephalothoracic has become much flatter and wider, has lost all trace
of its previous segmentation, and has become distinctly trilobed. The
PCECILOPODA. 537
central lobe forms a well-marked keel, and at the line of insertion of the
rim-like edge of the lateral lobes are placed the two pairs of eyes (se and
ce). The abdominal region is also distinctly trilobed and divided into nine
segments ; the last, which is merely formed of a median process, being the
rudiment of the caudal spine. The edges of the second to the seventh are
armed with a spine. The changes in the appendages are not very considerable. The anterior pair nearly meet in the middle line in front or
the mouth ; and the latter structure is completely covered by an upper
lip. Each abdominal appendage of the second pair is provided with four
gill-lamellas, attached close to its base.
Three weeks after hatching an ecdysis takes place, and the larva passes
from a trilobite into a limuloid form. The segmentation of the abdomen
has become much less obvious, and this part of the embryo closely resembles its permanent form. The caudal spine is longer, but is still relatively
short. A fourth pair of abdominal appendages is established, and the first
pair have partially coalesced, while the second and third pairs have become
jointed, their outer ramus containing four and their inner three joints.
Additional gill-lamellae attached to the two basal joints of the second and
third abdominal appendages have appeared.
The further changes are not of great importance. They are effected in
a series of successive moults. The young larvae swim actively at the
surface.
Our, in many respects, imperfect knowledge of the development of
Limulus is not sufficient to shew whether it is more closely related to the
Crustacea or to the Arachnida, or is an independent phylum.
The somewhat Crustacean character of biramous abdominal feet, etc.
is not to be denied, but at the same time the characters of the embryo
appear to me to be decidedly more arachnidan than crustacean. The
embryo, when the appendages are first formed, has a decidedly arachnidan facies. It will be remembered that when the limbs are first formed
they are all post-oral. They resemble in this respect the limbs of the
Arachnida, and it seems to be probable that the anterior pair is equivalent
to the cheliceras of Arachnida, which, as shewn in a previous section, are
really post-oral appendages in no way homologous with antennae 1 .
The six thoracic appendages may thus be compared with the six
Arachnidan appendages; which they resemble in their relation to the
mouth, their basal cutting blades, etc.
The existence of abdominal appendages behind the six cephalothoracic
does not militate against the Arachnidan affinities of Limulus, because in
the Arachnida rudimentary abdominal appendages are always present in
the embryo. The character of the abdominal appendages is probably
1 Dohrn believes that he has succeeded in shewing that the first pair of appendages
of Limulus is innervated in the embryo from the supra-cesophageal ganglia. His
observations do not appear to me conclusive, and, arguing from what we know of the
development of the Arachnida, the innervation of these appendages in the adult can be
of no morphological importance.
538 PYCNOGONIDA.
secondarily adapted to an aquatic respiration, since it is likely (for the
reasons already mentioned in connection with the Tracheata) that if Limulus
has any affinities with the stock of the Tracheata it is descended from airbreathing forms, and has acquired its aquatic mode of respiration. The
anastomosis of the two halves of the generative glands is an Arachnidan
character, and the position of the generative openings in Limulus is more
like that in the Scorpion than in Crustacea.
A fuller study of the development would be very likely to throw
further light on the affinities of Limulus, and if Packard's view about the
nature of the inner egg membrane were to be confirmed, strong evidence
would thereby be produced in favour of the Arachnidan affinities.
(533) A. Dohrn. "Untersuch. Ub. Bau u. Entwick. d. Arthropoden (Limulus
polyphemus)." Jenaische Zeitschrift, Vol. vi., 1871.
(534) A. S. Packard. "The development of Limulus polyphemus." Mem.
Boston Soc. Nat. History, Vol. II., 1872.
PYCNOGONIDA.
The embryos, during the first phases of their development, are always
carried by the male in sacks which are attached to a pair of appendages
(the third) specially formed for this purpose. The segmentation of the
ovum is complete, and there is in most forms developed within the eggshell a larva with three pairs of two-jointed appendages, and a rostrum
placed between the front pair.
It will be convenient to take Achelia kevis, studied by Dohrn (No. 536),
as type.
The larva of Achelia when hatched is provided with the typical three
pairs of appendages. The foremost of them is chelate, and the two following pairs are each provided with a claw. Of the three pairs of larvalappendages Dohrn states that he has satisfied himself that the anterior is
innervated by the supra-cesophageal ganglion, and the two posterior by
separate nerves coming from two imperfectly united ventral ganglia. The
larva is provided with a median eye formed of two coalesced pigment
spots, and with a simple stomach.
The gradual conversion of the larva into the adult takes place by the
elongation of the posterior end of the body into a papilla, and the formation there, at a later period, of the anus ; while at the two sides of the
anal papilla rudiments of a fresh pair of appendages the first pair of ambulatory limbs of the adult make their appearance. The three remaining
pairs of limbs become formed successively as lateral outgrowths, and their
development is accomplished in a number of successive ecdyses. As they
are formed caeca from the stomach become prolonged into them. For each
of them there appears a special ganglion. While the above changes are
taking place the three pairs of larval appendages undergo considerable
reduction. The anterior pair singly becomes smaller, the second loses
its claw, and the third becomes reduced to a mere stump. In the adult the
PENTASTOMIDA. 539
second pair of appendages becomes enlarged again and forms the so-called
palpi, while the third pair develops in the male into the egg-carrying appendages, but is aborted in the female. The first pair form appendages lying
parallel to the rostrum, which are sometimes called pedipalpi and sometimes antennae.
The anal papilla is a rudimentary abdomen, and, as Dohrn has shewn,
contains rudiments of two pairs of ganglia.
The larvae of Phoxichilidium are parasitic in various Hydrozoa (Hydractinia, etc.). After hatching they crawl into the Hydractinia stock. They
are at first provided with the three normal pairs of larval appendages. The
two hinder of these are soon thrown off, and the posterior part of the trunk,
with the four ambulatory appendages belonging to it, becomes gradually
developed in a series of moults. The legs, with the exception of the hindermost pair, are fully formed at the first ecdysis after the larva has become
free. In the genus Pallene the metamorphosis is abbreviated, and the'
young are hatched with the full complement of appendages.
The position of the Pycnogonida is not as yet satisfactorily settled.
The six-legged larva has none of the characteristic features of the Nauplius,
except the possession of the same number of appendages.
The number of appendages (7) of the Pycnogonida does not coincide
with that of the Arachnida. On the other hand, the presence of chelate
appendages innervated in the adult by the supra-cesophageal ganglia rather
points to a common phylum for the Pycnogonida and Arachnida ; though as
shewn above (p. 455) all the appendages in the embryo of true Arachnida
are innervated by post-oral ganglia. The innervation of these appendages
in . the larvae of Pycnogonida requires further investigation. Against
such a relationship the extra pair of appendages in the Pycnogonida is
no argument, since the embryos of most Arachnida are provided with four
such extra pairs. The two groups must no doubt have diverged very
early.
BIBLIOGRAPHY.
(535) G. Cavanna. " Studie e ricerche sui Picnogonidi." Pubblicazioni del R.
Institute di Studi stiperiori in Firenze, 1877.
(536) An. Dohrn. " Ueber Entwickhuig u. Baud. Pycnogoniden." Jenaische
Zeitschrift, Vol. v. 1870, and " Neue Untersuchungen lib. Pycnogoniden." Mitthdl.
a. d. zoologischen Station zu Neafel, Bd. I. 1878.
(537) G. Hodge. " Observations on a species of Pycnogon, etc." Annal. and
Mag. of Nat. Hist. Vol. ix. 1862.
(538) C. Semper. " Ueber Pycnogoniden u. ihre in Hydroiden schmarotzenden
Larvenformen." Arbeiten a. d. zool.-zoot. Instit. Wiirzburg, Vol. I. 1874.
PENTASTOMIDA.
The development and metamorphosis of Pentastomum taenoides have
been thoroughly worked out by Leuckart (No. 540) and will serve as type
for the group.
540 PENTASTOMIDA.
In the sexual state it inhabits the nasal cavities of the dog. The early
embryonic development takes place as the ovum gradually passes down the
uterus. The segmentation appears to be complete ; and gives rise to an
oval mass in which the separate cells can hardly be distinguished. This
gradually differentiates itself into a characteristic embryo, divided into a tail
and trunk. The tail is applied to the ventral surface of the trunk, and on
the latter two pairs of stump-like unsegmented appendages arise, each
provided with a pair of claws. At the anterior extremity of the body is
formed the mouth, with a ventral spine and lateral hook, which are perhaps
degenerated jaws. The spine functions as a boring apparatus, and an
apparatus with a similar function is formed at the end of the tail. A larval
cuticle now appears, which soon becomes detached from the embryo, except
on the dorsal surface, where it remains firmly united to a peculiar papilla.
This papilla becomes eventually divided into two parts, one of which remains
attached to the cuticle, while the part connected with the embryo forms a
raised cross placed in a cup- shaped groove. The whole structure has been
compared, on insufficient grounds, to the dorsal organ of the Crustacea.
The eggs, containing the embryo in the condition above described, are
eventually carried out with the nasal slime, and, if transported thence into
the alimentary cavity of a rabbit or hare, the embryos become hatched by
the action of the gastric juice. From the alimentary tract of their new host
they make their way into the lungs or liver. They here become enveloped
in a cyst, in the interior of which they undergo a very remarkable metamorphosis. They are, however, so minute and delicate that Leuckart was
unable to elucidate their structure till eight weeks after they had been
swallowed. At this period they are irregularly-shaped organisms, with a
most distant resemblance to the earlier embryos. They are without their
previous appendages, but the alimentary tract is now distinctly differentiated.
The remains of two cuticles in the cyst seem to shew that the above changes
are effected in two ecdyses.
In the course of a series of ecdyses the various organs of the larval form
known as Pentastomum denticulatum continue to become differentiated.
After the first (= third) ecdysis the cesophageal nerve-ring and sexually
undifferentiated generative organs are developed. At the fourth (=sixth)
ecdysis the two pairs of hooks of the adult are formed in pockets which
appeared at a somewhat earlier stage ; and the body acquires an annulated
character. At a somewhat earlier period rudiments of the external generative organs indicate the sex of the larva.
After a number of further ecdyses, which are completed in about six
months after the introduction of the embryos into the intermediate host, the
larva attains its full development, and acquires a form in which it has long
been known as Pentastomum denticulatum. It now leaves its cyst and
begins to move about. It is in a state fit to be introduced into its final host ;
but if it be not so introduced it may become encysted afresh.
If the part of a rabbit or hare infected by a Pentastomum denticulatum
be eaten by a dog or wolf, the parasite passes into the nasal cavity of the
TARDIGRADA. 541
latter, and after further changes of cuticle becomes a fully-developed sexual
Pentastomum taenioides, which does not differ to any very marked extent
from P. denticulatum.
In their general characters the larval migrations of Pentastomum are
similar to those of the Cestodes.
The internal anatomy of the adult Pentastomum, as well as the
characters of the larva with two pairs of clawed appendages, are perhaps
sufficient to warrant us in placing it with the Arthropoda, though it would
be difficult to shew that it ought not to be placed with such a form as
Myzostomum (vide p. 369). There do not appear to be any sufficient
grounds to justify its being placed with the Mites amongst the Arachnida.
If indeed the rings of the body of the Pentastomida are to be taken as
implying a true segmentation, it is clear that the Pentastomida cannot be
associated with the Mites.
BIBLIOGRAPHY.
(539) P. J. van Beneden. " Recherches s. 1'organisation et le developpement d.
Linguatules." Ann. d. Sden. Nat., 3 Ser., Vol. XI.
(540) R. Leuckart. " Bau u. Entwicklungsgeschichte d. Pentastomen." Leipzig
and Heidelberg. 1860.
TARDIGRADA.
Very little is known with reference to the development of the Tardigrada.
A complete and regular segmentation (von Siebold, Kaufmann, No. 541) is
followed by the appearance of a groove on the ventral side indicating a
ventral flexure. At about the time of the appearance of the groove the cells
become divided into an epiblastic investing layer and a central hypoblastic
mass.
The armature of the pharynx is formed very early at the anterior
extremity, and the limbs arise in succession from before backwards.
The above imperfect details throw no light on the systematic position of
this group.
Tardigrada.
(541) J. Kaufmann. " Ueber die Entwicklung u. systematische Stellung d.
Tardigraden." Zeit.f. wiss, ZooL, Bd. HI. 1851.
Summary of Arthropodan Development.
The numerous characters common to the whole of the
Arthropoda led naturalists to unite them in a common phylum,
but the later researches on the genealogy of the Tracheata and
Crustacea tend to throw doubts on this conclusion, while there
is not as yet sufficient evidence to assign with certainty a
definite position in either of these classes to the smaller groups
described in the present chapter. There seems to be but little
542 SUMMARY.
doubt that the Tracheata are descended from a terrestrial Annelidan type related to Peripatus. The affinities of Peripatus to
the Tracheata are, as pointed out in a previous chapter (p. 386),
very clear, while at the same time it is not possible to regard
Peripatus simply as a degraded Tracheate, owing to the fact
that it is provided with such distinctly Annelidan organs as
nephridia, and that its geographical distribution shews it to be a
very ancient form.
The Crustacea on the other hand are clearly descended from
a Phyllopod-like ancestor, which can be in no way related to
Peripatus.
The somewhat unexpected conclusion that the Arthropoda
have a double phylum is on the whole borne out by the anatomy
of the two groups. Without attempting to prove this in detail,
it may be pointed out that the Crustacean appendages are
typically biramous, while those of the Tracheata are never at
any stage of development biramous 1 ; and the similarity between
the appendages of some of the higher Crustacea and those of
many Tracheata is an adaptive one, and could in no case be
used as an argument for the affinity of the two groups.
The similarity of many organs is to be explained by both
groups being descendants of Annelidan ancestors. The similarity of the compound eye in the two groups cannot however
be explained in this way, and is one of the greatest difficulties
of the above view. It is moreover remarkable that the eye of
Peripatus 2 is formed on a different type to either the single or
compound eyes of most Arthropoda.
The conclusion that the Crustacea and Tracheata belong to
two distinct phyla is confirmed by a consideration of their
development. They have no doubt in common a centrolecithal
segmentation, but, as already insisted on, the segmentation is
no safe guide to the affinities.
In the Tracheata the archenteron is never, so far as we
know, formed by an invagination 3 , while in Crustacea the
1 The biflagellate antennae of Pauropus amongst the Myriapocls can hardly be
considered as constituting an exception to this rule.
3 I hope to shew this in a paper I am preparing on the anatomy of Peripatus.
8 Stecker's description of an invagination in the Chilognatha cannot be accepted
without further confirmation ; -vide p. 388.
SUMMARY. 543
evidence is in favour of such an invagination being the usual,
and, without doubt, the primitive, mode of origin.
The mesoblast in the Tracheata is formed in connection with
a median thickening of the ventral plate. The unpaired plate
of mesoblast so formed becomes divided into two bands, one on
each side of the middle line.
In both Spiders and Myriopods, and probably Insects, the
two plates of mesoblast are subsequently divided into somites,
the lumen of which is continued into the limbs.
In Crustacea the mesoblast usually originates from the walls
of the invagination, which gives rise to the mesenteron.
It does not become divided into two distinct bands, but
forms a layer of scattered cells between the epiblast and hypoblast, and does not usually break up into somites ; and though
somites are stated in some cases to be found they do not
resemble those in the Tracheata.
The proctodaeum is usually formed in Crustacea before and
rarely later 1 than the stomodaeum. The reverse is true for the
Tracheata. In Crustacea the proctodseum and stomodaeum,
especially the former, are very long, and usually give rise to the
greater part of the alimentary tract, while the mesenteron is
usually short.
In the Tracheata the mesenteron is always considerable, and
the proctodaeum is always short. The derivation of the Malpighian bodies from the proctodaeum is common to most
Tracheata. Such diverticula of the proctodaeum are not found
in Crustacea.
1 This is stated to be the case in Moina (Grobben).
CHAPTER XX.
ECHINODERMATA 1 .
THE development of the Echinodermata naturally falls into
two sections:
(i) The development of the germinal layers and of the
systems of organs; (2) the development of the larval appendages
and the metamorphosis.
The Development of the Germinal Layers and of tJie Systems
of Organs.
The development of the systems of organs presents no very
important variations within the limits of the group.
Holothuroidea. The Holothurians have been most fully
studied (Selenka, No. 563), and may be conveniently taken as
type.
The segmentation is nearly regular, though towards its close,
and in some instances still earlier, a difference becomes apparent
between the upper and the lower poles.
At the close of segmentation (fig. 247 A) the egg has a
nearly spherical form, and is constituted of a single layer of
columnar cells enclosing a small segmentation cavity. The
lower pole is slightly thickened, and the egg rotates by means of
fine cilia.
An invagination now makes its appearance at the lower
pole (fig. 247 B), and simultaneously there become budded off
from tJie cells undergoing the invagination amoeboid cells, which
1 The following classification of the Echinodermata is employed in this chapter.
I. Holothuroidea. IV. Echinoidea.
II. Asteroidea. V. Crinoidea.
III. Ophiuroidea.
ECHINODERMATA. 545
eventually form the muscular system and the connective tissue.
These cells very probably have a bilaterally symmetrical origin.
This stage represents the gastrula stage which is common to all
Echinoderms. The invaginated sack is the archenteron. As it
grows larger one side of the embryo becomes flattened, and the
other more convex. On the flattened side a fresh invagination
FIG. 247. TWO STAGES IN THE DEVELOPMENT OF HOLOTHURIA TUBULOSA
VIEWED IN OPTICAL SECTION. (After Selenka.)
A. Blastosphere stage at the close of segmentation. B. Gastrula stage.
mr. micropyle ; //. chorion; s.c. segmentation cavity; bl. blastoderm; ep. epiblast;
hy. hypoblast; ms. amoeboid cells derived from hypoblast ; a.e. archenteron.
arises, the opening of which forms the permanent mouth, the
opening of the first invagination remaining as the permanent
anus (fig. 248 A).
These changes give us the means of attaching definite names
to the various parts of the embryo. It deserves to be noted in
the first place that the embryo has assumed a distinctly bilateral
form. There is present a more or less concave surface extending from the mouth to near the anus, which will be spoken
of as the ventral surface. The anus is situated at the posterior
extremity. The convex surface opposite the ventral surface
forms the dorsal surface, which terminates anteriorly in a
rounded prse-oral prominence.
It will be noticed in fig. 248 A that in addition to the
primitive anal invagination there is present a vesicle (?/.).
This vesicle is directly formed by a constriction of the primitive
B. II. 35
54 6
HOLOTHUROIDEA.
archenteron (fig. 249 Vpv.), and is called by Selenka the vasoperitoneal vesicle. It gives origin to the epithelioid lining of
the body cavity and water-vascular system of the adult 1 . In the
parts now developed we have the rudiments of all the adult organs.
The mouth and anal involutions (after the separation of the
vaso-peritoneal vesicle) meet and unite, a constriction indicating
their point of junction (fig. 248 B). Eventually the former gives
FIG. 248. THREE STAGES IN THE DEVELOPMENT OF HOLOTHURIA TUBULOSA
VIEWED FROM THE SIDE IN OPTICAL SECTION. (After Selenka.)
tn. mouth; oe. oesophagus; st. stomach; i. intestine; a. anus; I.e. longitudinal
ciliated band; v.p. vaso-peritoneal vesicle; p.v. peritoneal vesicle; p.r. right peritoneal vesicle ; //. left peritoneal vesicle ; w.v. water- vascular vesicle ; p. dorsal pore
of water- vascular system ; ms. muscle cells.
rise to the mouth and cesophagus, and the latter to the remainder of the alimentary canal 2 .
The vaso-peritoneal vesicle undergoes a series of remarkable
changes. After its separation from the archenteron it takes
up a position on the left side of this, elongates in an anteroposterior direction, and from about its middle sends a narrow
diverticulum towards the dorsal surface of the body, where an
1 The origin of the vaso-peritoneal vesicle is not quite the same in all the species.
In Holothuria tubulosa it is separated from the csecal end of the archenteron; the
remainder of which then grows towards the oral invagination. In Cucumaria the
archenteron forks (fig. 249) ; and one fork forms the vaso-peritoneal vesicle, and the
other the major part of the mesenteron.
2 There appears to be some uncertainty as to how much of the larval cesophagus is
derived from the stomodaeal invagination.
ECHINODERMATA.
547
opening to the exterior becomes formed (fig. 248 B, /.). The
diverticulum becomes the madreporic canal, and the opening
the dorsal pore.
The vaso-peritoneal vesicle next divides into two, an anterior vesicle (fig. 248 B, w.v.), from which is derived the
epithelium of the water-vascular system, and a posterior (fig.
248 B, /.?;.), which gives rise to the epithelioid lining of the body
cavity. The anterior vesicle (fig. 248 C, w.v.) becomes fivelobed, takes a horseshoe-shaped form, and grows round the
oesophagus (fig. 256, w.v.r). The five lobes form the rudiments
of the water-vascular prolongations into the tentacles. The
remaining parts of the water-vascular system are also developed
as outgrowths of the original vesicle. Five of these, alternating
with the original diverticula, form the five ambulacral canals,
from which diverticula are produced into the ambulacral feet ; a
sixth gives rise to the Polian vesicle. The remaining parts of
the original vesicle form the water-vascular ring.
We must suppose that eventually the madreporic canal loses
its connection with the exterior so as to hang loosely in the
interior, though the steps of this process do not appear to
have been made out.
The original hinder peritoneal vesicle grows rapidly,
and divides into two (fig. 248 C,
pi. and pr.}, which encircle the
two sides of the alimentary
canal, and meet above and
below it. The outer wall of
each of them attaches itself to
the skin, and the inner one to
the alimentary canal and watervascular system ; in both cases
the walls remain separated
from the adjacent parts by a
layer of the amoeboid cells
already spoken of. The cavity
of the peritoneal vesicles becomes the permanent body
cavity. Where the walls of
-ME
FIG. 249. LONGITUDINAL SECTION
THROUGH AN EMBRYO OF CUCUMARIA
DOLIOLUM AT THE END OF THE FOURTH
DAY.
Vpv. vaso-peritoneal vesicle; ME.
mesenteron; Blp., Ptd. blastopore, proctodaeum.
352
548 HOLOTHUROIDEA.
the two vesicles meet on the dorsal side, a mesentery, suspending the alimentary canal and dividing the body cavity longitudinally, is often formed. In other parts the partition walls
between the two sacks appear to be absorbed.
The amoeboid cells, which were derived from the invaginated
cells, arrange themselves as a layer round all the organs (fig.
249). Some of them remain amoeboid, attach themselves to the
skin, and form part of the cutis; and in these cells the calcareous spicula of the larva and adult are formed. Others
form the musculature of the larval alimentary tract, while the
remainder give rise to the musculature and connective tissue of
the adult.
The development of the vascular system is not known, but the discovery
of Kowalevsky, confirmed by Selenka, that from the walls of the watervascular system corpuscles are developed, identical with those in the bloodvessels, indicates that it probably develops in connection with the watervascular system. The observations of Hoffmann and Perrier on the communication of the two systems in the Echinoidea point to the same conclusion.
Though nothing very definite is known with reference to the development of
the nervous system, Metschnikoff suggests that it develops in connection
with the thickened bands of epiblast which are formed by a metamorphosis
of the ciliated bands of the embryo, and accompany the five radial tubes
(vide p. 555). In any case its condition in the adult leaves no doubt of its
being a derivative of the epiblast.
From the above description the following general conclusions
may be drawn :
(1) The blastosphere stage is followed by a gastrula stage.
(2) The gastrula opening forms the permanent anus, and the
mouth is formed by a fresh invagination.
(3) The mesoblast arises entirely from the invaginated cells,
but in two ways :
(a) As scattered amoeboid cells, which give origin to the
muscles and connective tissue (including the cutis) of the body
wall and alimentary tract.
(&) As a portion separated off from the archenteron,
which gives rise both to the epithelioid lining of the body cavity,
and of the water-vascular system.
(4) The oesophagus is derived from an invagination of the
epiblast, and the remainder of the alimentary canal from the
archenteron.
ECHINODERMATA. 549
(5) The embryonic systems of organs pass directly into those
of the adult.
The development of Synapta diverges, as might be expected, to a very
small extent from that of Holothuria.
Asteroidea. In Asterias the early stages of development conform to
our type. There arise, however, two bilaterally symmetrical vaso-peritoneal
diverticula from the archenteron. These diverticula give rise both to the
lining of the body cavity and water-vascular system. With reference to
the exact changes they undergo there is, however, some difference of opinion.
Agassiz (543) maintains that both vesicles are concerned in the formation of
the water-vascular system, while Metschnikoff (560) holds that the watervascular system is entirely derived from the anterior part of the larger left
vesicle, while the right and remainder of the left vesicle form the body
cavity. MetschnikofFs statements appear to be the most probable. The
anterior part of the left vesicle, after separating from the posterior, grows
into a five-lobed rosette (fig. 260, /), and a madreporic canal (h] with a dorsal
pore opening to the exterior. The rosette appears not to grow round the
oesophagus, as in the cases hitherto described. But the latter is stated to
disappear, and a new oesophagus to be formed, which pierces the rosette,
and places the old mouth in communication with the stomach. Except
where the anus is absent in the adult, the larval anus probably persists.
Ophiuroidea. The early development of the Ophiuroidea is not so
fully known as that of other types. Most species have a free-swimming
larva, but some (Amphiura) are viviparous.
The early stages of the free-swimming larvae have not been described,
but I have myself observed in the case of Ophiothrix fragilis that the
segmentation is uniform, and is followed by the normal invagination. The
opening of this no doubt remains as the larval anus, and there are probably
two outgrowths from this to form the vaso-peritoneal vesicles. Each of these
divides into two parts, an anterior lying close to the oesophagus, and a
posterior close to the stomach. The anterior on the right side aborts ; that
on the left side becomes the water-vascular vesicle, early opens to the
exterior, and eventually grows round the oesophagus, which, as in Holothurians, becomes the oesophagus of the adult. The posterior vesicles give rise
to the lining of the body cavity, but are stated by Metschnikoff to be at first
solid, and only subsequently to acquire a cavity the permanent body cavity.
The anus naturally disappears, since it is absent in the adult. In the
viviparous type the first stages are imperfectly known, but it appears that
the blastopore vanishes before the appearance of the mouth. The development of the ^vaso-peritoneal bodies takes place as in the free-swimming
larvae.
Echinoidea. In the Echinoidea (Agassiz, No. 542, Selenka, No. 564)
there is a regular segmentation and the normal invagination (fig. 250 A).
The amoeboid mesoblast cells arise as two laterally placed masses, and give
rise to the usual parts. The archenteron grows forward and bends towards
550
CRINOIDEA.
the ventral side (fig. 250 B). It becomes (fig. 250 C) divided into three
chambers, of which the two hindermost (d and c) form the stomach and
intestine ; while the anterior forms the oesophagus, and gives rise to the
FIG. 250. THREE SIDE VIEWS OF EARLY STAGES IN THE DEVELOPMENT OF
STRONGYLOCENTRUS. (From Agassiz.)
a, anus (blastopore) ; d. stomach ; o. oesophagus ; c . rectum ; w. vaso-peritoneal
vesicle ; v. ciliated ridge ; r. calcareous rod.
vaso-peritoneal vesicles. These latter appear as a pair of outgrowths
(fig. 251), but become constricted off as a single two-horned vesicle, which
subsequently divides into two. The left of these
is eventually divided, as in Asteroids, into a
peritoneal and water-vascular sack, while the
right forms the right peritoneal sack. An oral
invagination on the flattened ventral side meets
the mesenteron after its separation from the
vaso-peritoneal vesicle. The larval anus persists, as also does the larval mouth, but owing
to the manner in which the water-vascular
rosette is established the larval oesophagus appears to be absorbed, and to be replaced by a
fresh oesophagus.
Crinoidea. Antedon, the only Crinoid
so far studied (Gotte, No. 549), presents some
not inconsiderable variations from the usual
Echinoderm type. The blastopore is placed on
the somewhat flattened side of the oval blastosphere, and not, as is usual, at the hinder end.
The blastopore completely closes, and is not converted into the permanent anus. The archenteron gives rise to the epithelioid lining of both body
cavity and water-vascular system. These parts do not, however, appear as
a single or paired outgrowth from the archenteron, but as three distinct
outgrowths which are not formed contemporaneously. Two of them are first
FIG. -251. DORSO-VENTRAL VIEW OF AN EARLY
LARVA OF STRONGYLOCENTRUS. (From Agassiz.)
a. anus ; d. stomach ; o.
oesophagus ; w. vaso-peritoneal vesicle; r. calcareous
rod.
ECHINODERMATA.
551
formed and become the future body cavity; but their lumens remain distinct.
Jngmally appearing as lateral outgrowths, the right one assumes a dorsal
position and sends a prolongation into the stalk (fig. 252 rp'\ and
the left one assumes first a ventral, and then an oral position (fur
252 lp\
The third outgrowth of the archenteron gives rise to the water-vascular
vesicle. It first grows round the region of the future oesophagus and so
forms the water-vascular ring.
The wall of the ring then
grows towards the body wall
so as to divide the oral (left)
peritoneal vesicle into two
distinct vesicles, an anterior
and a posterior, shewn in fig.
253, lp' and lp. Before this
division is completed, the
water-vascular ring is produced in front into five pro
FIG. 252. LONGITUDINAL SECTION THROUGH
AN ANTEDON LARVA. (From Carpenter: after
Gotte.)
al. mesenteron ; -wv. water- vascular ring ;
lp. left (oral) peritoneal vesicle; rp. right peritoneal vesicle ; rp'. continuation of right vesicle
into the stalk ; st. stalk.
cessesthe future tentacles
(fig. 252, wv) which project
into the cavity of the oral
vesicle (lp\ After the oral
peritoneal space has become
completely divided into two parts, the anterior dilates (fig. 253, //) greatly,
and forms a large vestibule at the anterior end of the body. This vestibule
(lp'} next acquires a communication with the mesenteron, shewn in fig. 253
at m. The anterior wall of this vestibule is finally broken through. By this
rupture the mesenteron is placed in communication with the exterior by the
opening at m, while at the same time the tentacles of the water-vascular ring
(/) project freely to the exterior. Such is Gotte's account of the prge-oral
body space, but, as he himself points out, it involves our believing that the
lining of the diverticulum derived from the primitive alimentary vesicle
becomes part of the external skin. This occurrence is so remarkable, that
more evidence appears to me requisite before accepting it.
The formation of the anus occurs late. Its position appears to be the
same as that of the blastopore, and is indicated by a papilla of the mesenteron attaching itself to the skin on the ventral side (fig. 253, an). It eventually becomes placed in an interradial space within the oral disc of the adult.
The water-vascular ring has no direct communication with the exterior, but
the place of the madreporic canal of other types appears to be taken in
the larva by a single tube leading from the exterior into the body cavity, the
external opening of which is placed on one of the oral plates (vide p. 571) in
the next interradial space to the right of the anus, and a corresponding
diverticulum of the water-vascular ring opening into the body cavity. The
line of junction between the left and right peritoneal vesicles forms in the
larva a ring-like mesentery dividing the oral from the aboral part of the body
552
CRINOIDEA.
cavity. In the adult 1 the oral section of the larval body cavity becomes the
ventral part of the circumvisceral division of the body cavity, and the
subtentacular canals of the arms and disc ; while the aboral section becomes
the dorsal part of the circumvisceral division of the body cavity, the cceliac
canals of the arms, and the cavity of the centro-dorsal piece. The primitive
,+wr
FIG. 253. LONGITUDINAL SECTION THROUGH THE CALYX OF AN ADVANCED
PENTRACRINOID ANTEDON LARVA WITH CLOSED VESTIBULE.
(From Carpenter ; after Gotte.)
ae. epithelium of oral vestibule; ;//. mouth; al. mesenteron; an. rudiment of
permanent anus; lp. posterior part of left (oral) peritoneal sack; lp' '. anterior part of
left (oral) peritoneal sack; wr. water-vascular ring; /. tentacle; mt. mesentery;
rp. right peritoneal sack; rp '. continuation of right peritoneal sack into the stalk;
r. roof of tentacular vestibule.
distinction between the sections of the larval body cavity becomes to a large
extent obliterated, while the axial and intervisceral sections of the bodycavity of the adult are late developments.
The more important points in the development indicated in
the preceding pages are as follows :
(i) The blastosphere is usually elongated in the direction
of the axis of invagination, but in Comatula it is elongated
transversely to this axis.
1 Vide P. H. Carpenter, "On the genus Actinometra." Linnean Trans., and
Series, Zoology, Vol. n., Part I., 1879.
ECHINODERMATA. 553
(2) The blastopore usually becomes the permanent anus,
but it closes at the end of larval life (there being no anus in the
adult) in Ophiuroids and some Asteroids, while in Comatula it
closes very early, and a fresh anus is formed at the point where
the blastopore was placed.
(3) The larval mouth always becomes the mouth of the
adult.
(4) The archenteron always gives rise to outgrowths which
form the peritoneal membrane and water-vascular systems. In
Comatula there are three such outgrowths, two paired, which
form the peritoneal vesicles, and one unpaired, which forms the
water-vascular vesicle. In Asteroids and Ophiuroids there are
two outgrowths. In Ophiuroids both of these are divided into a
peritoneal and a water-vascular vesicle, but the right watervascular vesicle atrophies. In Asteroids only one water-vascular
vesicle is formed, which is derived from the left peritoneal vesicle.
In Echinoids and Holothuroids there is a single vaso-peritoneal
vesicle.
(5) The water- vascular vesicle grows round the larval
oesophagus in Holothuroids, Ophiuroids, and Comatula ; in
these cases the larval oesophagus is carried on into the adult.
In other forms the water-vascular vesicle forms a ring which
does not enclose the cesophagus (Asteroids and Echinoids);
in such cases a new oesophagus is formed, which perforates this
ring.
Development of the larval appendages and metamorphosis.
Holothuroidea. The young larva of Synapta, to which J.
Muller gave the name Auricularia (fig. 255), is in many respects
the simplest form of Echinoderm larva. With a few exceptions
the Auricularia type of larva is common to the Holothuria.
It is (fig. 254 A and fig. 255) bilaterally symmetrical, presenting a flattened ventral surface, and a convex dorsal one.
The anus (an) is situated nearly at the hinder pole, and the
mouth (m) about the middle of the ventral surface. In front
of the mouth is a considerable process, the prae-oral lobe.
Between the mouth and anus is a space, more or less concave
according to the age of the embryo, interrupted by a ciliated
554
AURICULARIA.
A similar ciliated ridge is
A E
ridge a little in front of the anus,
present on the ventral surface
of the prae-oral lobe immediately in front of the mouth.
The anal and oral ridges are
connected by two lateral ciliated bands, the whole forming
a continuous band, which,
since the mouth lies in the
centre of it (fig. 255), may be
regarded as a ring completely
surrounding the body behind
the mouth, or more naturally
as a longitudinal ring.
The bilateral Auricularia
is developed from a slightly
elongated gastrula with an uniform covering of cilia. The
gastrula becomes flattened on the oral side. At the same time
the cilia become specially developed on the oral and anal ridges,
and then on the remainder of the ciliated ring, while they are
FIG. 254. A. THE LARVA OF A HOLOTHUROID. B. THE LARVA OF AN ASTEROID.
;//. mouth; st. stomach; a. anus; l.c>
primitive longitudinal ciliated band; pr.c.
prae-oral ciliated band.
FIG. 155. DIAGRAMMATIC FIGURES REPRESENTING THE EVOLUTION OF AN
AURICULARIA FROM THE SIMPLEST ECHINODERM LARVAL FORM. (Copied from
MUller.)
The black line represents the ciliated ridge. The shaded part is the oral side of
the ring, the clear part the aboral side.
/;;. mouth; an. anus.
simultaneously obliterated elsewhere ; and so a complete Auricularia is developed. The water-vascular ring in the fully-developed
larva has already considerably advanced in the growth round the
oesophagus (fig. 256 w.v.r).
Most Holothurian larvae, in their transformation from the
bilateral Auricularia form to the radial form of the adult, pass
through a stage in which the cilia form a number of transverse
ECHINODERMATA.
555
-2>.v
rings, usually five in number, surrounding the body. The
stages in this metamorphosis are shewn in figs. 256, 257, and
258.
The primitive ciliated band,
at a certain stage of the metamorphosis, breaks up into a
number of separate portions
(fig. 256), the whole of which are
placed on the ventral surface.
Four of these (fig. 257 A and B)
arrange themselves in the form
of an angular ring round the
mouth, which at this period projects considerably. The remaining portions of the primitive
band change their direction from
a longitudinal one to a transverse (fig. 257 B), and eventually
grow into complete rings (fig.
2570). Of these there are five.
The middle one (257 B) is the
first to develop, and is formed
from the dorsal parts of the
primitive ring. The two hinder
rings develop next, and last of
all the two anterior ones, one of
which appears to be in front of the mouth (fig. 257 C).
The later development of the mouth, and of the ciliated ridge
surrounding it, is involved in some obscurity. It appears from
Metschnikoff (No. 560) that an invagination of the oesophagus
takes place, carrying with it the ciliated ridge around the mouth.
This ridge becomes eventually converted into the covering for
the five tentacular outgrowths of the water- vascular ring (fig.
258), and possibly also forms the nervous system.
The opening of the cesophageal invagination is at first behind
the foremost ciliated ring, but eventually comes to lie in front of
it, and assumes a nearly terminal though slightly ventral position
(fig. 258). No account has been given of the process by which
this takes place, but the mouth is stated by Metschnikoff (though
FIG. 256. FULL-GROWN LARVA OF
SYNAPTA. (After Metschnikoff.)
m. mouth ; st. stomach ; a. anus ;
p.v. left division of perivisceral cavity,
which is still connected with the watervascular system ; w.v.r. water-vascular
ring which has not yet completely encircled the oesophagus; I.e. longitudinal
part of ciliated band ; pr.c. prae-oral part
of ciliated band.
556
BIPINNARIA.
Miiller differs from him on this point) to remain open throughout. The further changes in the metamorphosis are not considerable. The ciliated bands disappear, and a calcareous ring
of ten pieces, five ambulacral and five interambulacral, is formed
round the oesophagus. A provisional calcareous skeleton is also
developed.
All the embryonic systems of organs pass in this case
directly into those of the adult.
The metamorphosis of most Holothuroidea is similar to that just
described. In Cucumaria (Selenka) there is however no Auricularia stage,
and the uniformly ciliated stage is succeeded by one with five transverse
FIG. 257. THREE STAGES IN THE DEVELOPMENT OF SYNAPTA. A and B
are viewed from the ventral surface, and C from the side. (After Metschnikoff.)
m. mouth; oe. oesophagus; pv. walls of the perivisceral cavity; wv. longitudinal
vessel of the water- vascular system; p. dorsal pore of water-vascular system;
cr. ciliated ring formed round the mouth from parts of the primitive ciliated
band.
bands of cilia, and a prae-oral and an anal ciliated cap. The mouth is at
first situated ventrally behind the prse-oral cap of cilia, but the prae-oral
cap becomes gradually absorbed, and the mouth assumes a terminal
position.
In Psolinus (Kowalevsky) there is no embryonic ciliated stage, and the
adult condition is attained without even a metamorphosis. There appear to
ECHINODERMATA.
557
be five plates surrounding the
mouth, which are developed before
any other part of the skeleton, and
are regarded by P. H. Carpenter
(No. 548) as equivalent to the five
oral plates of the Crinoidea. The
larval condition with ciliated bands
is often spoken of as the pupa stage,
and during it the larvae of Holothurians proper use their embryonic
tube feet to creep about.
Asteroidea. The commonest and most thoroughly
investigated form of Asteroid
larva is a free swimming form
known as Bipinnaria.
This form in passing from
the spherical to the bilateral
condition passes through at
first almost identical changes
to the Auricularian larva.
The cilia become at an early
period confined to an oral
and anal ridge.
The anal ridge gradually extends dorsalwards, and finally
forms a complete longitudinal post-oral ring (fig. 259 A) ; the
oral ridge also extends dorsalwards, and forms a closed prae-oral
ring (fig. 259 A), the space within which is left unshaded in my
figure.
The presence of two rings instead of one distinguishes the
Bipinnaria from the Auricularia. The two larvae are shewn side
by side in fig. 254, and it is obvious that the two bands of the
Bipinnaria are (as pointed out by Gegenbaur) equivalent to the
single band of the Auricularia divided into two. Ontologically,
however, the two bands of Bipinnaria do not appear to arise
from the division of a single band.
As the Bipinnaria grows older, a series of arms grows out
along lines of the two ciliated bands (fig. 259 C), and, in many
cases, three special arms are formed, not connected with the
ciliated bands, and covered with warts. These latter arms are
FlG. 258. A LATE STAGE IN THE DEVELOPMENT OF SYNAPTA. (After Metschnikoff.)
The figure shews the vestibular cavity
with retracted tentacles ; the ciliated bands ;
the water-vascular system, etc.
p. dorsal pore of water-vascular system ;
pv. walls of perivisceral cavity; ms. amoeboid cells.
558
BIPINNARIA.
known as brachiolar arms, and the larvae provided with them
as Brachiolaria (fig. 259 D).
As a rule the following arms can be distinguished (fig. 259 C and D), on
the hinder ring (Agassiz' nomenclature) a median anal pair, a dorsal anal
pair, and a ventral anal pair, a dorsal oral pair, and an unpaired anterior
dorsal arm ; on the prae-oral ring a ventral oral pair, and sometimes (Miiller)
an unpaired anterior ventral arm.
The three brachiolar arms arise as processes from the base of the
unpaired dorsal arm, and the two ventral oral arms. The extent of the
development of the arms varies with the species.
FIG. 259. DIAGRAMMATIC REPRESENTATION OF VARIOUS FORMS OF ASTEROID
LARWE. A, B, C, BIPINNARIA; D, BRACHIOLARIA. (Copied from Muller.)
The black lines represent the ciliated bands ; and the shading the space between
the prae-oral and the post-oral bands.
m. mouth; an. anus.
The changes by which the Bipinnaria or Brachiolaria becomes
converted into the adult starfish are very much more complicated
than those which take place in Holothurians. For an accurate
knowledge of them we are largely indebted to Alex. Agassiz
(No. 543). The development of the starfish takes place entirely
at the posterior end of the larva close to the stomach.
On the right and dorsal side of the stomach, and externally
to the rig/it peritoneal space, are formed five radially situated
calcareous rods arranged in the form of a somewhat irregular
pentagon. The surface on which they are deposited has a
spiral form, and constitutes together with its calcareous rods, the
ECHINODERMATA. 559
abactinal or dorsal surface of the future starfish. Close to its
dorsal, i.e. embryonic dorsal, edge lies the dorsal pore of the
water-vascular system (madreporic canal), and close to its ventral
edge the anus. On the left and ventral side of the stomach is
placed the water-vascular rosette, the development of which was
described on p. 549. It is situated on the actinal or ventral surface
of the future starfish, and is related to the left peritoneal vesicle.
Metschnikoff (No. 560) and Agassiz (No. 543) differ slightly as to the
constitution of the water- vascular rosette. The former describes and figures
it as a completely closed rosette, the latter states that ' it does not form a
completely closed curve but is always open, forming a sort of twisted
crescent-shaped arc.'
The water-vascular rosette is provided with five lobes, corresponding to which are folds in the larval skin, and each lobe
corresponds to one of the calcareous plates developed on the
abactinal disc. The plane of the actinal surface at first meets
that of the abactinal at an acute or nearly right angle. The two
surfaces are separated by the whole width of the stomach. The
general appearance of the larva from the ventral surface after
the development of the water-vascular rosette (i) and abactinal
disc (A) is shewn in fig. 260.
As development proceeds the abactinal surface becomes a
firm and definite disc, owing to the growth of the original
calcareous spicules into more or less definite plates, and to the
development of five fresh plates nearer the centre of the disc and
interradial in position. Still later a central calcareous plate
appears on the abactinal surface, which is thus formed of a
central plate, surrounded by a ring of five interradial plates, and
then again by a ring of five radial plates. The abactinal disc
now also grows out into five short processes, separated by five
shallow notches. These processes are the rudiments of the five
arms, and each of them corresponds to one of the lobes of the
water-vascular rosette. A calcareous deposit is formed round
the opening of the water-vascular canal, which becomes the
madreporic tubercle 1 . At about this stage the absorption of the
larval appendages takes place. The whole anterior part of the
1 The exact position of the madreporic tubercle in relation to the abactinal plates
does not seem to have been made out. It might have been anticipated that it would
be placed in one of the primary interradial plates, but this does not seem to be the
case. The position of the anus is also obscure.
5 6o
BIPINNARIA.
larva with the great prae-oral lobe has hitherto remained
unchanged, but now it contracts and undergoes absorption, and
becomes completely withdrawn into the disc of the future starfish.
The larval mouth is transported into
the centre of the actinal disc. In the
larvae observed by Agassiz and Metschnikoff nothing was cast off, but the
whole absorbed.
According to M tiller and Koren and
Danielssen this is not the case in the larva
observed by them, but part of the larva is
thrown off, and lives for some time independently.
After the absorption of the larval
appendages the actinal and abactinal
surfaces of the young starfish approach
each other, owing to the flattening of
the stomach ; at the same time they
lose their spiral form, and become flat
discs, which fit each other. Each of
the lobes of the rosette of the watervascular system becomes one of the
radial water-vascular canals. It first
becomes five-lobed, each lobe forming
a rudimentary tube foot, and on each ^ d ctinal disc of youn Aste '
side of the middle lobe two fresh ones
next spring out, and so on in succession. The terminal median
lobe forms the tentacle at the end of the arm, and the eye is
developed at its base. The growth of the water-vascular canals
keeps pace with that of the arms, and the tube feet become
supported at their base by an ingrowth of calcareous matter.
The whole of the calcareous skeleton of the larva passes directly
into that of the adult, and spines are very soon formed on the
plates of the abactinal surface. The original radial plates,
together with the spines which they have, are gradually pushed
outwards with the growth of the arms by the continual addition
of fresh rows of spines between the terminal plate and the plate
next to it. It thus comes about that the original radial plates
persist at the end of the arms, in connection with the unpaired
FIG. 260. BIPINNARIA
LARVA OF AN ASTEROID. (From
Gegenbaur ; after Miiller.)
b. mouth ; a. anus ; h. madreporic canal ; t. ambulacral
rosette ; c . stomach ; d. g. e.
etc. arms of Bipinnaria ; A.
ECHINODERMATA. 561
tentacles which form the apex of the radial water-vascular
tubes.
It has already been mentioned that according to Metschnikoff (No. 560)
a new oesophagus is formed which perforates the water-vascular ring, and
connects the original stomach with the original mouth. Agassiz (No. 543)
maintains that the water-vascular ring grows round the primitive oesophagus.
He says " During the shrinking of the larva the long oesophagus becomes
" shortened and contracted, bringing the opening of the mouth of the larva
" to the level of the opening of the oesophagus, which eventually becomes
"the true mouth of the starfish." The primitive anus is believed by
Metschnikoff to disappear, but by Agassiz to remain. This discrepancy
very possibly depends upon these investigators having worked at different
species.
There is no doubt that the whole of the larval organs, with
the possible exception of the oesophagus, and anus (where absent
in the adult), pass directly into the corresponding organs of the
starfish and that the prae-oral part of the body and arms of the
larva are absorbed and not cast off.
In addition to the Bipinnarian type of Asteroid larva a series of other
forms has been described by Miiller (No. 561), Sars, Keren, and Danielssen
(No. 554) and other investigators, which are however very imperfectly
known. The best-known form is one first of all discovered by Sars in
Echinaster Sarsii, and the more or less similar larvae subsequently investigated by Agassiz, Busch, Miiller, Wyville Thomson, etc. of another species
of Echinaster and of Asteracanthion. These larvae on leaving the egg have
an oval form, and are uniformly covered by cilia. Four processes (or in
Agassiz' type one process) grow out from the body ; by these the larvae fix
themselves. In the case of Echinaster the larvae are fixed in the ventral
concavity of the disc of the mother, between the five arms, where a temporary brood-pouch is established. The main part of the body is converted
directly into the disc of the young starfish, while the four processes come to
spring from the ventral surface, and are attached to the water- vascular ring.
Eventually they atrophy completely. Of the internal structure but little is
known ; till the permanent mouth is formed, after the development of the
young starfish is pretty well advanced, the stomach has no communication
with the exterior.
A second abnormal type of development is presented by the embryo of
Pteraster miliaris, as described by Koren and Danielssen 1 . The larvae to
the number of eight to twenty develop in a peculiar pouch on the dorsal
surface of the body. The early stages are not known, but in the later ones
the whole body assumes a pentagonal appearance with a mouth at one edge
1 The following statements are taken from the abstract in Bronn's Thierreichs.
B. II. 36
5 62
OPHIUROID PLUTEUS.
of the disc. At a later stage the anus is formed on the dorsal side of an arm
opposite the mouth. The stomach is surrounded by a water-vascular ring,
from which the madreporic canal passes to the dorsal surface, but does not
open. At a later stage the embryonic mouth and anus vanish, to be replaced
by a permanent mouth and anus in the normal positions.
A third, and in some respects very curious, form is a worm like larva of
Miiller, which is without bands of cilia. The dorsal surface of the youngest
larva is divided by transverse constrictions into five segments. On the
under side of the first of these is a five-lobed disc, each lobe being provided
with a pair of tube feet.
At a later period only three segments are visible on the dorsal surface,
but the ventral surface has assumed a pentagonal aspect. The later stages
are not known.
Ophiuroidea. The full-grown larva of the Ophiuroids is
known as a Pluteus. It commences with the usual more or less
spherical form ; from this it passes to a form closely resembling
FIG. 261. DIAGRAMMATIC FIGURES SHEWING THE EVOLUTION OK AN OPHIUROID PLUTEUS FROM A SIMPLE ECHINODERM LARVA. (Copied from Miiller.) The
calcareous skeleton is not represented.
///. mouth; an. anus; d. anterior arms; d'. lateral arms; e'. posterior arms; tf.
anterolateral arms.
that of Auricularia with a rounded dorsal surface, and a flattened
ventral one. Soon however it becomes distinguished by the
growth of a post-anal lobe and the absence of a prae-oral lobe
(fig. 261 B). The post-anal lobe forms the somewhat rounded
apex of the body. In front of the mouth, and between the
mouth and anus, arise the anal and oral ciliated ridges, which
soon become continued into a single longitudinal ciliated ring.
At the same time the body becomes prolonged into a series of
ECHINODERMATA.
563
processes along the ciliated band, which is continued to the
extremity of each. The primitive ciliated ring never becomes
broken up into two or more rings. A ciliated crown is usually
developed at the extremity of the post-anal lobe. The arms are
arranged in the form of a ring surrounding the mouth, and are
all directed forwards.
The first arms to appear are two lateral ones, which usually remain the
most conspicuous (fig. 261 B and C, cf\ Next arises a pair on the sides of
the mouth, which may be called the mouth or anterior arms (C, d}. A pair
ventral to and behind the lateral arms is then formed, constituting the
posterior arms (D, e'\ and finally a pair between the lateral arms and the
anterior, constituting the anterolateral arms (D,^).
The concave area between the arms forms the greater part of
the ventral surface of the body. Even before the appearance of
any of the arms, and before the formation of the mouth, two
calcareous rods are formed, which meet behind at the apex of
the post-anal lobe, and are continued as a central support into
each of the arms as they are successively formed. These rods
are shewn at their full development in fig. 262. The important
points which distinguish a Pluteus
larva from the Auricularia or
Bipinnaria are the following :
(i) The presence of the postanal lobe at the hind end of the
body. (2) The slight development of a prae-oral lobe. (3) The
provisional calcareous skeleton in
the larval arms.
Great variations are presented
in the development of the arms
and provisional skeleton. The
presence of lateral arms is however
a distinctive characteristic of the
Ophiuroid Pluteus. The other
arms may be quite absent, but
the lateral arms never.
The formation of the permanent Ophiuroid takes place in
much the same way as in the Asteroidea.
36-2
FIG. 262.
OPHIUROID.
after Miiller.)
PLUTEUS LARVA OF AN
(From Gegenbaur ;
A. rudiment of young Ophiuroid ;
(?. lateral arms; d. anterior arms;
e . posterior arms.
564
OPHIUROID PLUTEUS.
There is formed (fig. 262) on the right and dorsal side of stomach the
abactinal disc supported by calcareous plates, at first only five in number
and radial in position 1 . The disc is at first not symmetrical, but becomes so
at the time of the resorption of the larval arms. It grows out into five
processes the five future rays. The original five radial plates remain as the
terminal segments of the adult rays, and new plates are always added
between the ultimate and penultimate plate (Mu'ller), though it is probable
that in the later stages fresh plates are added in the disc.
The ventral surface of the permanent Ophiuroid is formed by the concave
surface between the mouth and anus. Between this and the stomach is
FIG. 263. DIAGRAMMATIC FIGURES SHEWING THE EVOLUTION OF ECHINOID
PLUTEI. (Copied from Miiller.) The calcareous skeleton is not represented. E.
Pluteus of Spatangus.
m. mouth; an. anus; d. anterior arms; d' . point where lateral arms arise in the
Ophiuroid Pluteus; e. anterointernal arms; e. posterior arms; g'. anterolateral arms;
g. anteroexternal arms.
situated the water-vascular ring. It is at first not closed, but is horseshoeshaped, with five blind appendages (fig. 262). It eventually grows round
the cesophagus, which, together with the larval mouth, is retained in the
adult. The five blind appendages become themselves lobed in the same
way as in Asterias, and grow out along the five arms of the disc and become
the radial canals and tentacles. All these parts of the water-vascular system
are of course covered by skin, and probably also surrounded by mesoblast
cells, in which at a later period the calcareous plates which lie ventral to the
radial canal are formed. The larval anus disappears. As long as the larval
appendages are not absorbed the ventral and dorsal discs of the permanent
Ophiuroid fit as little as in the case of the Brachiolaria, but at a certain
period the appendages are absorbed. The calcareous rods of the larval arms
1 Whether interradial plates are developed as in Asterias is not clear. They seem
to be found in Ophiopholis bellis, Agassiz, but have not been recognised in other
forms (vide Carpenter, No. 548, p. 369).
ECHINODERMATA. 565
break up, the arms and anal lobe become absorbed, and the dorsal and
ventral discs, with the intervening stomach and other organs, are alone left.
After this the discs fit together, and there is thus formed a complete young
Ophiuroid.
The whole of the internal organs of the larva (except the anus), including
the mouth, cesophagus, the body cavity, etc. are carried on directly into the
adult.
The larval skeleton is, as above stated, absorbed.
The viviparous larva of Amphiura squamata does not differ very greatly
from the larvae with very imperfect arms. It does not develop a distinct
ciliated band, and the provisional skeleton is very imperfect. The absence
of these parts, as well as of the anus, mentioned on p. 549, may probably be
correlated with the viviparous habits of the larva. With reference to the
passage of this larva into the adult there is practically nothing to add to
what has just been stated. When the development of the adult is fairly
advanced the part of the body with the provisional skeleton forms an
elongated rod-like process attached to the developing disc. It becomes
eventually absorbed.
Echinoidea. The Echinus larva (fig. 263} has a Pluteus
form like that of the Ophiuroids, and in most points, such as the
FIG. 264. Two LARV/E OF STRONGYLOCENTRUS. (From Agassiz.)
m. mouth; a. anus; o. cesophagus; d. stomach; c. intestine; '. and v. ciliated
ridges; iv. water- vascular tube; r. calcareous rods.
presence of the anal lobe, the ciliated band, the provisional
skeleton, etc., develops in the same manner. The chief difference
between the two Pluteus forms concerns the development of the
lateral arms. These, which form the most prominent arms in
the Ophiuroid Pluteus, are entirely absent in the Echinoid
5 66
ECHINOID PLUTEUS.
Pluteus, which accordingly has, as a rule, a much narrower form
than the Ophiuroid Pluteus.
A pair of ciliated epaulettes on each side of and behind the
ciliated ring is very characteristic of some Echinoid larvae.
They are originally developed from the ciliated ring (fig. 266 A
FIG. 265. LATERAL AND VENTRAL VIEW OF A LARVA OF STRONGYLOCENTRUS.
(From Agassiz.) General references as in fig. 264.
b. dorsal opening of madreporic canal; e '. posterior arms ; e'". anterior arms;
f lV . anterointernal arms.
and B, z>"). The presence of three processes from the anal lobe
supported by calcareous rods is characteristic of the Spatangoid
Pluteus (fig. 263 E).
The first two pairs of arms to develop, employing the same names as in
Ophiuroids, are the anterior attached to the oral process (fig. 263 C, d] and
the posterior pair (*?') A pair of anterolateral arms next becomes developed
(j^). A fourth pair (not represented in Ophiuroids) appears on the inner
side of the anterior pair forming an anterointernal pair (e}, and in the
Spatangoid Pluteus a fifth pair may be added on the external side of the
anterior pair forming an anteroexternal pair (g).
Each of the first-formed paired calcareous rods is composed of three
processes, two of which extend into the anterior and posterior arms ; and the
third and strongest passes into the anal lobe, and there meets its fellow
(fig. 265). A transverse bar in front of the arms joins the rods of the two
sides meeting them at the point where the three processes diverge. The
process in the anterolateral arm (fig. 266 B) is at first independent of this
system of rods, but eventually unites with it. Although our knowledge of
ECHINODERMATA. 567
the Pluteus types in the different groups is not sufficient to generalise with
great confidence, a few points seem to have been fairly determined 1 . The
Plutei of Strongylocentrus (figs. 266 and 267) and Echinus have eight arms
and four ciliated epaulettes. The only Cidaris-like form, the Pluteus of
which is known, is Arbacia : it presents certain peculiarities. The anal lobe
develops a pair of posterior (auricular) appendages, and the ciliated ring,
besides growing out into the normal eight appendages, has a pair of short
blunt anterior and posterior lobes. An extra pair of non-ciliated accessory
mouth arms appears also to be developed. Ciliated epaulettes are not
present. So far as is known the Clypeastroid larva is chiefly characterized
by the round form of the anal lobe. The calcareous rods are latticed. In the
Pluteus of Spatangoids there are (fig. 263) five pairs of arms around the
mouth pointing forwards, and three arms developed from the anal lobe
pointing backwards. One of these is unpaired, and starts from the apex of
the anal lobe. All the arms have calcareous rods which, in the case of the
posterior pair, the anterolateral pair, and the unpaired arm of the anal lobe,
are latticed. Ciliated epaulettes are not developed.
Viviparous larvae of Echinoids have been described by Agassiz 2 .
The development of the permanent Echinus has been chiefly worked out
by Agassiz and Metschnikoff.
In the Pluteus of Echinus lividus the first indication of the adult arises,
when three pairs of arms are already developed, as an invagination of the
skin on the left side, between the posterior and anterolateral arms, the
bottom of which is placed close to the water-vascular vesicle (fig. 266 B, u/\
The base of this invagination becomes very thick, and forms the ventral disc
of the future Echinus. The parts connecting this disc with the external
skin become however thin, and, on the narrowing of the external aperture of
invagination and the growth of the thickened disc, constitute a covering for
the disc, called by Metschnikoff the amnion. The water- vascular vesicle
adjoining this disc grows out into five processes, forming as many tube feet,
which cause the surface of the involuted disc to be produced into the same
number of processes. The external opening of the invagination of the disc
never closes, and after the development of the tube feet begins to widen
again, and the amnion to atrophy. Through the opening of the invagination
the tube feet now project. The dorsal and right surface of the Pluteus,
which extends so as to embrace the opening of the madreporic canal and
the anus, forms the abactinal or dorsal surface of the future Echinus
(fig. 267, a). This disc fits on to the actinal invaginated surface which arises
on the left side of the Pluteus. On the right surface of the larva (dorsal of
permanent Echinus) two pedicellariae appear, and at a later period spines
are formed, which are at first arranged in a ring-like form round the edge of
the primitively flat test. While these changes are taking place, and the two
surfaces of the future Echinus are gradually moulding themselves so as to
1 Vide especially Muller, Agassiz, and Metschnikoff.
2 For viviparous Echini vide Agassiz, Proc. Amer. Acad. 1876.
5 68
ECHINOID PLUTEUS.
form what is obviously a young Echinus, the arms of the Pluteus with their
contained skeleton have been gradually undergoing atrophy. They become
irregular in form, their contained skeleton breaks up into small pieces, and
they are gradually absorbed.
The water-vascular ring is from the first complete, so that, as in
Asterias, it is perforated through the centre by a new oesophagus. According
FIG. 266. SIDE AND DORSAL VIEW OF A LARVA OF STRONGYLOCENTRUS.
(From Agassiz.) General reference letters as in figs. 264 and 265.
e" . anterolateral arms; v" '. ciliated epaulettes; ?&'. invagination to form the disc
of Echinus.
to Agassiz the first five tentacles or tube feet grow into the radial canals,
and form the odd terminal tentacles exactly as in Asterias 1 . Spatangus
only differs in development from Echinus in the fact that the opening of the
invagination to form the ventral disc becomes completely closed, and that
the tube feet have eventually to force their way through the larval epidermis
of the amnion, which is ruptured in the process and eventually thrown
off.
Crinoidea. The larva of Antedon, while still within the
egg-shell, assumes an oval form and uniform ciliation. Before it
1 Gotte (No. 549) supported by Muller's and Krohn's older, and in some points
extremely erroneous observations, has enunciated the view that the radial canals in
Echinoids and Holothuroids have a different nature from those in Asteroids and
Ophiuroids.
ECHINODERMATA.
569
becomes hatched the uniform layer of cilia is replaced by four
transverse bands of cilia, and a tuft of cilia at the posterior
extremity. In this condition it escapes from the egg-shell
FIG. 267. FULL-GROWN LARVA OF STRONGYLOCENTRUS. (From Agassiz.)
The figure shews the largely-developed abactinal disc of the young Echinus
enclosing the larval stomach. Reference letters as in previous figs.
(fig. 268 A), and becomes bilateral, owing to a flattening of the
ventral surface. On the flattened surface appears a ciliated
570
CRINOID LARVA.
depression corresponding in position with the now closed blastopore (vide p. 550). The third ciliated band bends forward
to pass in front of this (fig. 269). Behind the last ciliated band
there is present a small depression of unknown function, also
FIG. 768. THREB STAGES IN THE DEVELOPMENT OF ANTEDON (COMATULA.)
(From Lubbock; after Thomson.)
A. larva just hatched; B. larva with rudiment of the calcareous plates; C. Pentacrinoid larva.
ECHINODERMATA.
571
situated on the ventral surface. The posterior extremity of the
embryo elongates to form the rudiment of the future stem, and
a fresh depression, marking the position of the future mouth,
makes its appearance on the anterior and ventral part.
While the ciliated bands are still at their full development,
the calcareous skeleton of the future calyx makes its appearance
in the form of two rows, each of five plates, formed of a network
of spicula (figs. 268 B and 269). The plates of the anterior ring
are known as the orals, those of the posterior as the basals.
The former surround the left, i.e. anterior
peritoneal sack ; the latter the right, i.e.
posterior peritoneal sack. The two rows
of plates are at first not quite transverse,
but form two oblique circles, the dorsal
end being in advance of the ventral.
The rows soon become transverse, while
the originally somewhat ventral oral
surface is carried into the centre of the
area enclosed by the oral plates.
By the change in position of the
original ventral surface relatively to the
axis of the body, the bilateral symmetry
of the larva passes into a radial symmetry. While the first skeletal elements
of the calyx are being formed, the
skeleton of the stem is also established.
The terminal plate is first of all established, then the joints, eight at first, of
the stem. The centro-dorsal plate is
stated by Thomson to be formed as the
uppermost joint of the stem 1 . The larva, after the completion
of the above changes, is shewn in fig. 268 B, and somewhat more
diagrammatically in fig. 269.
After the above elements of the skeleton have become established the ciliated bands undergo atrophy, and shortly after
1 Gotte (No. 549) on the other hand holds that the centro-dorsal plate is developed
by the coalescence of a series of at first independent rods, which originate simultaneously with, and close to, the lower edges of the basals, and that it is therefore
similar in its origin to the basals.
FIG. 269. LARVA OF
ANTEDON WITH RUDIMENTS
OF CALCAREOUS SKELETON.
(From Carpenter; after
Thomson.)
i. Terminal plate at the
end of the stem ; 3. basals ;
or. orals ; bl. position of blastopore.
572
CRINOID LARVA.
wards the larva becomes attached by the terminal plate of its
stem. It then passes into the Pentacrinoid stage! The larva in
this stage is shewn in fig. 268 C and fig. 270. New joints are
added at the upper end of the stem next the calyx, and a new
element the radials makes its appearance as a ring of five
small plates, placed in the space between the basals and orals,
and in the intervals alternating with them
(fig. 270, 4). The roof of the oral vestibule (vide fig. 253 and p. 551) has in
the meantime become ruptured ; and
the external opening of the mouth thus
becomes established. Surrounding the
mouth are five petal-like lobes, each of
them supported by an oral plate (fig.
268 C). In the intervals between them
five branched and highly contractile tentacles, which were previously enclosed
within the vestibule, now sprout out :
they mark the position of the future
radial canals, and are outgrowths of the
water-vascular ring. At the base of each
of them a pair of additional tentacles is
soon formed. Each primary tentacle corresponds to one of the radials. These
latter are therefore, as their name implies,
radial in position; while the basals and
orals are interradial. In addition to the
contractile radial tentacles ten non-contractile tentacles, also diverticula of the
water- vascular ring, are soon formed, two
for each interradius.
In the course of the further development the equatorial space between the FlG - 2 7<>. YOUNG PEN
. TACRINOID LARVA OF AN
orals and the basals enlarges, and gives TEDON. (From Carpenter ;
rise to a wide oral disc, the sides of which after w >' ville Thom s"-)
- , , . ... . i. terminal plate of stem;
are formed by the radials resting on the c d. centro-donal plate; 3 .
basals; while in the centre of it are bftsals J 4- radials; or. orals.
placed the five orals, each with its special lobe.
The anus, which is formed on the ventral side in the position
ECHINODERMATA. 573
of the blastopore (p. 551), becomes surrounded by an anal plate,
which is interradial in position, and lies on the surface of the
oral disc between the orals and radials. On the oral plate in
the next interradius is placed the opening of a single funnel
leading into the body cavity, which Ludwig regards as equivalent to the opening of the madreporic canal (vide p. 55 1) 1 .
From the edge of the vestibule the arms grow out, carrying
with them the tentacular prolongation of the water-vascular ring.
Two additional rows of radials are soon added.
The stalked Pentacrinoid larva becomes converted, on the
absorption of the stalk, into the adult Antedon. The stalk is
functionally replaced by a number of short cirri springing from
the centro-dorsal plate. The five basals coalesce into a single
plate, known as the rosette, and the five orals disappear, though
the lobes on which they were placed persist. In some stalked
forms, e.g. Rhizocrinus Hyocrinus, the orals are permanently
retained. The arms bifurcate at the end of the third radial, and
the first radial becomes in Antedon rosacea (though not in all
species of Antedon) concealed from the surface by the growth of
the centro-dorsal plate. An immense number of funnels, leading
into the body cavity, are formed in addition to the single one
present in the young larva. These are regarded by Ludwig as
equivalent to so many openings of the madreporic canal ; and
there are developed, in correspondence with them, diverticula of
the water-vascular ring.
Comparison of Echinoderm Larvce and General Conclusions.
In any comparison of the various types of Echinoderm larvae
it is necessary to distinguish between the free-swimming forms,
and the viviparous or fixed forms. A very superficial examination suffices to shew that the free-swimming forms agree very
much more closely amongst themselves than the viviparous
1 I have made no attempt to discuss the homologies of the plates of the larval
Echinodermata because the criteria for such a discussion are still in dispute. The
suggestive memoirs of P. H. Carpenter (No. 548) on this subject may be consulted by
the reader. Carpenter attempts to found his homologies on the relation of the plates
to the primitive peritoneal vesicles, and I am inclined to believe that this method of
dealing with these homologies is the right one. Ludwig (No. 559) by regarding the
opening of the madreporic canal as a fixed point has arrived at very different results.
574
COMPARISON OF ECHINODERM LARV.-E.
forms. We are therefore justified in concluding that in the
viviparous forms the development is abbreviated and modified.
All the free forms are nearly alike in their earliest stage after
the formation of the archenteron. The surface between the
anus and the future mouth becomes flattened, and (except in
Antedon, Cucumaria, Psolinus, etc. which practically have an
abbreviated development like that of the viviparous forms) a
ridge of cilia becomes established in front of the mouth, and a
second ridge between the mouth and the anus. This larval
form, which is shewn in fig. 264 A, is the type from which the
various forms of Echinoderm larvae start.
In all cases, except in Bipinnaria, the two ciliated ridges
soon become united, and constitute a single longitudinal postoral ciliated ring.
The larvae in their further growth undergo various changes,
and in the later stages they may be divided into two groups :
(1) The Pluteus larva of Echinoids and Ophiuroids.
(2) The Auricularia (Holothuroids) and Bipinnaria (Asteroids) type.
The first group is characterized by the growth of a number
of arms more or less surrounding the mouth, and supported
by calcareous rods. The ciliated band retains its primitive
condition as a simple longitudinal band throughout larval life.
There is a very small prae-oral lobe, while an anal lobe is very
largely developed.
The Auricularia and Bi- A. B
pinnaria resemble each other
in shape, in the development
of a large prae-oral lobe, and
in the absence of provisional
calcareous rods ; but differ in
the fact that the ciliated band
is single in Auricularia (fig
271 A), and is double in Bipinnaria (fig. 271 B).
TheBipinnarialarvashews
THUROID. B. THE LARVA OF AN ASTEa great tendency to develop RIAS.
soft arms; while in the Auri- . ' mouth; st. stomach; a. anus; I.e.
, . ,_, , *_ 1-1- primitive longitudinal ciliated band; pr.c.
cularia the longitudinal ciliat- p r3 e-oral ciliated band.
FlG
THE LARVA OF A
ECHINODERMATA. 575
ed band breaks up into a number of transverse ciliated bands.
This condition is in .some instances reached directly, and such
larvae undoubtedly approximate to the larvae of Antedon, in
which the uniformly ciliated condition is succeeded by one with
four transverse bands, of which one is prae-oral.
All or nearly all Echinoderm larvae are bilaterally symmetrical,
and since all Echinodermata eventually attain a radial symmetry, a change necessarily takes place from the bilateral to the
radial type.
In the case of the Holothurians and Antedon, and generally
in the viviparous types, this change is more or less completely
effected in the embryonic condition ; but in the Bipinnaria and
Pluteus types a radial symmetry does not become apparent till
after the absorption of the larval appendages. It is a remarkable fact, which seems to hold for the Asteroids, Ophiuroids, Echinoids, and Crinoids, that the dorsal side of the larva is
not directly converted into the dorsal disc of the adult; but
the dorsal and right side becomes the adult dorsal or abactinal
surface, while the ventral and left becomes the actinal or ventral
surface.
It is interesting to note with reference to the larvae of the
Echinodermata that the various existing types of larvae must
have been formed after the differentiation of the existing groups
of the Echinodermata ; otherwise it would be necessary to adopt
the impossible position that the different groups of Echinodermata were severally descended from the different types of larvae.
The various special appendages, etc. of the different larvae have
therefore a purely secondary significance; and their atrophy
at the time of the passage of the larva into the adult, which
is nothing else but a complicated metamorphosis, is easily explained.
Originally, no doubt, the transition from the larva to the
adult was very simple, as it is at present in most Holothurians ;
but as the larvae developed various provisional appendages, it
became necessary that these should be absorbed in the passage
to the adult state.
It would obviously be advantageous that their absorption
should be as rapid as possible, since the larva in a state of
transition to the adult would be in a very disadvantageous
576 COMPARISON OF ECHINODERM
position. The rapid metamorphosis, which we find in Asteroids,
Ophiuroids, and Echinoids in the passage from the larval to the
adult state, has no doubt arisen for this reason.
In spite of the varying provisional appendages possessed by
Echinoderm larvae it is possible, as stated above (p. 574), to
recognise a type of larva, of which all the existing Echinoderm
larval forms are modifications. This type does not appear to
me to be closely related to that of the larvae of any group
described in the preceding pages. It has no doubt certain
resemblances to the trochosphere larva of Chaetopoda, Mollusca,
etc., but the differences between the two types are more striking
than the resemblances. It firstly differs from the trochosphere
larva in the character of the ciliation. Both larvae start from the
uniformly ciliated condition, but while the prae-oral ring is almost
invariable, and a peri-anal ring very common in the trochosphere;
in the Echinoderm larva such rings are rarely found ; and even
when present, i.e. the prae-oral ring of Bipinnaria and the terminal
though hardly peri-anal patch of Antedon, do not resemble
closely the more or less similar structures of the trochosphere.
The two ciliated ridges (fig. 264 A) common to all the Echinoderm larvae, and subsequently continued into a longitudinal ring,
have not yet been found in any trochosphere. The transverse
ciliated rings of the Holothurian and Crinoid larvae are of no
importance in the comparison between the trochosphere larvae
and the larvae of Echinodermata, since such rings are frequently
secondarily developed. Cf. Pneumodermon and Dentalium amongst Mollusca.
In the character of the prae-oral lobe the two types again
differ. Though the prae-oral lobe is often found in Echinoderm
larvae it is never the seat of an important (supra-oesophageal)
ganglion and organs of special sense, as it invariably is in the
trochosphere.
Nothing like the vaso-peritoneal vesicles of the Echinoderm
larvae has been found in the trochosphere ; nor have the characteristic trochosphere excretory organs been found in the Echinoderm larvae.
The larva which most nearly approaches those of the Echinodermata is the larva of Balanoglossus described in the next
chapter.
ECHINODERMATA. 577
BIBLIOGRAPHY.
(542) Alex. Agassiz. Revision of the Echini. Cambridge, U.S. 1872 74.
(543) Alex. Agassiz. " North American Starfishes." Memoirs of the Museum
of Comparative Anatomy and Zoology at Harvard College, Vol. v., No. i. 1877
(originally published in 1864).
(544) J. Barrois. " Embryogenie de 1'Asteriscus verruculatus " Journal dc
VAnat. et Phys. 1879.
(545) A. Baur. Beitrdge zur Naturgeschichte d. Synapta digitata. Dresden,
1864.
(546) H. G. Bronn. Klassen u. Ordnungen etc. Strahlenthiere, Vol. II. 1860.
(547) W. B. Carpenter. "Researches on the structure, physiology and development of Antedon." Phil. Trans. CLVI. 1866, and Proceedings of the Roy. Soc.,
No. 166. 1876.
(548) P. H. Carpenter. " On the oral and apical systems of the Echinoderms."
Quart. J. of Micr. Science, Vol. xvm. and xix. 18789.
(549) A. Gotte. " Vergleichende Entwicklungsgeschichte d. Comatula mediterranea." Arch, fur micr. Anat., Vol. xn. 1876.
(550) R. Greeff. "Ueber die Entwicklung des Asteracanthion rubens vom Ei
bis zur Bipinnaria u. Brachiolaria." Schriften d. Gesellschaft zur Beforderung d. gesammten Natunvissenschaften zu Marburg, Bd. xn. 1876.
(551) R. Greeff. "Ueber den Bau u. die Entwicklung d. Echinodermen." Sitz.
d. Gesell. z. Beforderung d. gesam. Naturwiss. zu Marburg, No. 4. 1879.
(552) T. H. Huxley. "Report upon the researches of Miiller into the anat.
anddevel. of the Echinoderms." Ann. and Mag. of Nat. Hist., 2nd Ser., Vol. vin.
1851.
(553) Koren and Danielssen. "Observations sur la Bipinnaria asterigera.
Ann. Scien. Nat., Ser. in., Vol. vii. 1847.
(554) Koren and Danielssen. "Observations on the development of the Starfishes." Ann. and Mag. of Nat. Hist., Vol. XX. 1857.
(555) A. Kowalevsky. " Entwicklungsgeschichte d. Holothurien. " Mhn.Ac.
Petersbourg, Ser. VII., Tom. XL, No. 6.
(556) A. Krohn. "Beobacht. a. d. Entwick. d. Holothurien u. Seeigel."
Miillers Archiv, 1851.
(557) A. Krohn. "Ueb. d. Entwick. d. Seesterne u. Holothurien." Miillcr's
Archiv, 1853.
(558) A. Krohn. "Beobacht. lib. Echinodermenlarven." Mailer's Archiv,
1854.
(559) H. Ludwig. "Ueb. d. primar. Steinkanal d. Crinoideen, nebst vergl.
anat. Bemerk. lib. d. Echinodermen." Zeit.f. wiss. ZooL, Vol. xxxiv. 1880.
(560) E. Metschnikoff. "Studien iib. d. Entwick. d. Echinodermen u.
Nemertinen." Mem. Ac. Petersboiirg, Series vii., Tom. xiv., No. 8. 1869.
(561) 1 Joh. Miiller. "Ueb. d. Larven u. d. Metamorphosed. Echinodermen."
Abhandlungen d. Berlin. Akad. (Five Memoirs), 1848, 49, 50, 52 (two Memoirs).
(562) Joh. Mtiller. "Allgemeiner Plan d. Entwicklung d. Echinodermen."
Abhandl. d. Berlin. Akad., 1853.
1 The dates in this reference are the dates of publication.
B. II. 37
578 BIBLIOGRAPHY.
(563) E. Selenka. "Zur Entwicklung d. Holothurien." Zeit. f. wiss. Zool.,
Bd. xxvii. 1876.
(564) E. Selenka. "Keimblatter u. Organanlage bei Echiniden." Zeit.f.-wiss.
Zool., Vol. xxxin. 1879.
(565) Sir Wyville Thomson. "On the Embryology of the Echinodermata."
Natural History Review, 1 864.
(566) Sir Wyville Thomson. "On the Embryogeny of Antedon rosaceus."
Phil. Trans. 1865.
CHAPTER XXI.
ENTEROPNEUSTA.
THE larva of Balanoglossus is known as Tornaria. The prselarval development is not known, and the youngest stage (fig.
272) so far described (Gotte, No. 569) has
many remarkable points of resemblance to
a young Bipinnaria.
A mouth (m\ situated on the ventral
surface, leads into an alimentary canal with
a terminal anus (an). A prae-oral lobe is
well developed, as in Bipinnaria, but there
is no post-anal lobe. The bands of cilia
have the same general form as in Bipinnaria. There is a prae-oral band, and a
longitudinal post-oral band ; and the two
bands nearly meet at the apex of the praeoral lobe (fig. 273). A contractile band
an
FIG. 272. EARLY
STAGE IN THE DEVELOPMENT OF TORNARIA.
(After Gotte.)
W. so-called watervascular vesicle developing as an outgrowth
of the mesenteron; m.
passes from the oesophagus to the apex of mouth; an. anus,
the prae-oral lobe, and a diverticulum (fig. 272, W) from the
alimentary tract, directed towards the dorsal surface, is present.
Contractile cells are scattered in the space between the body
wall and the gut.
In the following stage (fig. 274 A) a conspicuous transverse
post-oral band of a single row of long cilia is formed, and the
original bands become more sinuous. The alimentary diverticulum of the last stage becomes an independent vesicle opening
by a pore on the dorsal surface (fig. 274 A, w). The contractile
cord is now inserted on this vesicle. Where this cord joins the
apex of the prae-oral lobe between the two anterior bands of
cilia a thickening of the epiblast (? a ganglion) has become
372
580
ENTEROPNEUSTA.
C.C.
an.
FIG. 273. YOUNG TORNARIA.
(After Miiller.)
m. mouth ; an. anus ; w. watervascular vesicle ; oc. eye-spots ; c.c.
contractile cord.
established, and on it are placed
two eye-spots (fig. 273 oc, and
fig. 274 A). A deep bay is
formed on the ventral surface of
the larva.
As the larva grows older the
original bands of cilia become
more sinuous, and a second
transverse band with small cilia
is formed (in the Mediterranean
larva) between the previous
transverse band and the anus.
The water-vascular vesicle is
prolonged into two spurs, one
on each side of the stomach.
A pulsating vesicle or heart is
also formed (fig. 274 B, ht), and arises, according to Spcngel
(No. 572), as a thickening of the epidermis.
It subsequently becomes enveloped in a
pericardium, and is
placed in a depression
in the water-vascular
vesicle. Two pairs of
diverticula, one behind
the other, grow out
(Agassiz, No. 568) from
the gastric region of
the alimentary canal.
The two parts of each
pair form flattened
compartments, which
together give rise to a
complete investment of
the adjoining parts of
the alimentary tract.
The two parts of each
coalesce, and thus form
FlG. 274. TWO STAGKS IN THK 1 >KY KI.< >I'M KN I
OF TORNARIA. (After Metschnikoff.)
The black lines represent the ciliated hands.
m. mouth; an. anus; br. branchial cleft; ///.
heart ; c. Ixxly cavity between splanchnic and
somatic mesoblast layers; 7.-'. watcr-vascvilar vesicle:
v. circular blood-vessel.
ENTEROPNEUSTA.
5 8l
a double-walled cylinder round the alimentary tract, but their
cavities remain separated by a dorsal and ventral septum.
Eventually (Spengel) the cavity of the anterior cylinder
forms the section of the body cavity in the collar of the adult,
and that of the posterior (fig. 274 B, c) the remainder of the
body cavity. The septa, separating the two halves of each,
remain as dorsal and ventral mesenteries.
The conversion of Tornaria (fig. 274 A) into Balanoglossus
(fig. 274 B) is effected in a few hours, and consists mainly in
certain changes in configuration, and in the disappearance of
the longitudinal ciliated band.
The body of the young Balanoglossus (fig. 274 B) is divided
into three regions (i) the proboscidian region, (2) the collar,
(3) the trunk proper. The proboscidian region is formed by the
elongation of the prae-oral lobe into an oval body with the eyespots at its extremity, and provided with strong longitudinal
muscles. The heart (hi) and water-vascular vesicle lie near its
base, but the contractile cord connected with the latter is no longer
present. The mouth is placed on
the ventral side at the base of the
prae-oral lobe, and immediately behind it is the collar. The remainder
of the body is more or less conical,
and is still girt with the larval
transverse ciliated band, which lies
in the middle of the gastric region
in the Mediterranean species, but
in the cesophageal region in the
American one.
The whole of the body, including
the proboscis, becomes richly ciliated.
One of the most important cha- S us WITH FOUR BRANCHIAL
racters of the adult Balanoglossus CLEFTS * (After Alex. Agossiz.)
r . m. mouth ; an. anus ; br. bran
consists in the presence of respira- chial cleft . hL heart ; IV. watertory structures comparable with the vascular vesicle,
vertebrate gill slits. The earliest traces of these structures
are distinctly formed while the larva is still in the Tornaria
FIG. 275. LATE STAGE IN THE
DEVELOPMENT OF BALANOGLOS
582 I'N I'KUOl'NKUSTA.
condition, as one pair of pouches from the oesophagus in the
Mediterranean species, and four pairs in the American one
(fig. 275, br).
In the Mediterranean Tornaria the two pouches meet the
skin dorsally, and in the young Balanoglossus (fig. 274 B, br)
acquire an external opening on the dorsal side. In the American
species the first four pouches are without external openings
till additional pouches have been formed. Fresh gill pouches
continue to be formed both in the American and probably
the Mediterranean species, but the conversion of the simple
pouches into the complicated gill structure of the adult
has only been studied by Agassiz (No. 568) in the American
species. It would seem in the first place that the structure of
the adult gill slits is much less complicated in the American than
in the Mediterranean species. The simple pouches of the young
become fairly numerous. They are at first circular ; they then
become elliptical, and the dorsal wall of each slit becomes folded ;
subsequently fresh folds are formed which greatly increase the
complexity of the gills. The external openings are not acquired
till comparatively late.
Our knowledge of the development of the internal organs, mainly
derived from Agassiz, is still imperfect. The vascular system appears early
in the form of a dorsal and a ventral vessel, both pointed, and apparently
ending blindly at their two extremities. The two spurs of the water-vascular
vesicle, which in the Tornaria stage rested upon the stomach, now grow
round the oesophagus, and form an anterior vascular ring, which Agassiz
describes as becoming connected with the heart, though it still communicates
with the exterior by the dorsal pore and seems to become connected with the
remainder of the vascular system. According to Spengel (No. 572) the
dorsal vessel becomes connected with the heart, which remains through life
in the proboscis : the cavity of the water-vascular vesicle forms the cavity of
the proboscis in the adult, and its pore remains as a dorsal (not, as usually
stated, ventral) pore leading to the exterior.
The eye-spots disappear.
Tornaria is a very interesting larval form, since it is intermediate in structure between the larva of an Echinoderm and
trochosphere type common to the Mollusca, Chxtopoda, etc.
The shape of the body especially the form of the ventral
depression, the character of the longitudinal ciliated band, the
structure and derivation of the water-vascular vesicle, and the
ENTEROPNEUSTA. 583
formation of the walls of the body cavity as gastric diverticula,
are all characters which point to a connection with Echinodcrm
larvae.
On the other hand the eye-spots at the end of the prae-oral
lobe 1 , the contractile band passing from the oesophagus to the
eye-spots (fig. 273), the two posterior bands of cilia, and the
terminal anus are all trochosphere characters.
The persistence of the prae-oral lobe as the proboscis is
interesting, as tending to shew that Balanoglossus is the surviving representative of a primitive group.
*
BIBLIOGRAPHY.
(567) A. Agassiz. "Tornaria." Ann. Lyceum Nat. Hist.\u\. New York,
1866.
(568) A. Agassiz. "The History of Balanoglossus and Tornaria." Mem.
Amer. Acad. of Arts and Stien., Vol. IX. 1873.
(569) A. Gotte. " Entwicklangsgeschichte d. Comatula Mediterranea." Archiv
fur mikr. Anat., Bd. xii., 1876, p. 641.
(570) E. Metschnikoff. " Untersuchungen iib d. Metamorphose, etc. (Tornaria)." Zeit.fiir wiss. ZooL, Bd. xx. 1870.
(571) J. M tiller. " Ueb. d. Larven u. Metamor. d. Echinodermen." Berlin
Akad., 1849 and 1850.
(572) J. W. Spengel. "Ban u. Entwicklung von Balanoglossus. Tagebl. d.
Naturf. Vers. Miinchen, 1877.
1 It would be interesting to have further information about the fate of the thickening of epiblast in the vicinity of the eye-spots. The thickening should by rights be the
supra-oesophageal ganglion, and it does not seem absolutely impossible that it may give
rise to the dorso-median cord in the region of the collar, which constitutes, according
to Spengel, the main ganglion of the adult.
INDEX.
Abdominalia, 459, 493, 499
Acanthocephala, 379
Acanthosoma, 473, 474, 475
Acarina, 444, 454
Accipenser, 102
Achaeta, 319
Achelia, 538
Achtheres percarum, 490
Acineta, 7, 8
Acraspeda, 152, 165, 167, 178, 179, 182,
185, 186
Actinia, 169, 171, 179
Actinophrys, 9
Actinotrocha, 315, 318, 363, 364
Actinozoa, 26, 102, 152, j66, 170, 171,
172, 176, 178, 179, 181, 182, 186
Actinula, 155
Aculeata, 421
^Egineta flavescens, 158
yEginidae, 156, 158
^Eginopsis Mediterranea, 158
/Equorea Mitrocoma, 182
Agalma, 163
Agelena, 436, 450
Agelena labyrinthica, 119, 438
Alciope, 74
Alcippidae, 499
Alcyonaria, 152
Alcyonidse, 167, 168
Alcyonidium mytili, 297, 300, 302
Alcyonium palmatum, 119, 148, 167, 182
Alima, 484, 486
Amoeba, 19, 20
Amphibia, 22, 54, 56, 59, 60, 63, 66, 74,
83, 102
Amphilina, 218
Amphioxus, 54, 56, 59, 61, 66, 93, 426
Amphipoda, 518
Amphiporus lactifloreus, 202
Amphistomum, 31
,, subclavatum, 205
Amphitrochae, 330
Amphiura squamata, 565
Anchorella, 108, 492, 520
Anelasma squalicola, 499
Anguillulidse, 371
Annelida, 14, 25, 98, 503, 525
Anodon, 37, 38, 39, 100, 107, 259, 260,
265, 266, 268
Anopla, 189, 202
Anura, 5
Antedon, 568, 573, 574
Aphides, 15, 16, 76, 79, 116, 428, 429
Aphrodite, 42
Apis, 402, 407, 408, 412, 413
Aplysia, 99, 226, 238, 252, 253
Aplysinidaa, 146
Apoda, 459, 493
Aptera, 395, 420
Apus, 1 6, 79, 460, 463
Arachnida, 22, 114, 119, 413, 4.51, 435,
444, 454, 455, 458, 537, 539
Arachnitis, 171
Araneina, 50, 51, 436
Arbacia, 567
Area, 38
Archigetes, 218
Archizosea gigas, 494
Arenicola, 42
Argiope, 311, 312, 315, 317
Argonauta, 247, 248
Argulus, 492
Armata, 355
Arthropoda, 12, 16, 18, 22, 75, 77,79, 83,
108, no, 221, 382, 383, 434, 448,503,
5 2 5> 534 54', 54 2
Articulata, 311, 313, 316, 317
Ascaridiae, 371
Ascaris nigrovenosa, 16, 82
,, lumbricoides, 375
Ascetta, 144
Ascidia canina, 53
Ascidians, 74, 102, 208, 426
Asellus aquaticus, 112,120, 516
Astacus, 66, 465, 477, 511, 512, 513,
525
586
INDKX.
Asteracanthion, 69, 70, 561
Asterias, 20, 68, 69, 71, 78, 80, 84, 549,
564
Asteroidea, 35, 36, 544, 549, 557, 563,
576
Astnea, 169
Astroides, 169
Atax Bonzi, 445
Atlanta, 231, 240
Atrochae, 330
Aurelia, 167
Auricularia, 553, 554, 562, 574
Autolytus cornutus, 319, 343
Aves, 56, 59, 61, 64, 107. 109
Axolotl, 1 6
Balanoglossus, 576, 579, 581
Balanus balanoides, 75, 493
Belemnites, 252, 253
Bipinnaria, 557, 563, 574, 576, 579
Blatta, 374, 395
Bojanus, organ of, 264, 282
Bonellia, 20, 43, 44, 98, 324, 355, 358,
359
Bothriocephalus salmonis, 211
,, proboscideus, 212
Brachiella, 492
Brachiolaria, 558, 564
Brachiopoda, 311, 317, 318
Brachyura, 466, 480, 483
Branchiobdella, 42, 43, 346
Branchiogasteropoda, 272
Branchiopoda, 79, 459, 523, 524
Branchipus, 463, 524
Branchiura, 459, 492
Branchionus urceolaris, 221
Braula, 396
Uuccinum, 237, 280
Bulimus citrinus, 229
Bunodes, 169, 171
Buthus, 431
Calcispongiae, 138, 148
Calopteryx, 402
Calycophoridce, 152, 159
Calyptoblastic Hydroids, 184, 185
Calyptraea, 223, 280
Campanularidse, 183, 184
Capitclla, 330, 332
Carabidae, 476
Carcinus Mcenas, 481, 483
Cardium, 260, 262
" pygmaeum, 262
Carinaria, 240
Caryophyllium, 168, 171
pea, 165, 167
Cecidomyia, 15, 79, 416, 417, 429
Cephalopoda, 20, 40, 41, 102, 108, 109,
135. "5. 240, 242, 244, 250, 252, 253,
270, 271, 272, 274, 279, 282, 287
Cephalothrix galatheae, 202
Ceratosponguc, 146
Cercariae, 207, 208, 209
Cerianthus, 168, 171
Cestodes, 14, 29, 31, 32, 33, 189, 210,
212, 218, 313, 425, 541
Chsetogaster, 342
Chaetopoda, 5, 18, 23, 41, 43, 44 , 54,
67, 209, 215, 270, 275, 307, 312, 317,
318, 319, 320, 326, 334, 33<S, 342, 346,
349, 350, 351, 364. 369. 33, 36, 408,
448, 457, 458, 521, 576,582
ChiXitopteridte, 333
Cha^tosomoidea, 371
Chelifer, 434, 436, 442, 446, 454
Chermes, 15, 429
Chilognatha, 113, 387, 389, 391, 393,
395
Chilopoda, 387, 392, 394
Chilostomata, 292, 297, 298, 304, 305
Chironomus, 15, 378, 401, 402, 415, 416,
429
Chiton, 254, 256, 257, 273
Chordata, 5
Chrysaora, 165
Chthonius, 436
Cicada, 395
Cirripedia, 459, 492, 496,503, 509, 520
Cladocera, 459, 464, 519
Clausilia, 239
Clavella, 520
Clavularia crassa, 167
Cleodora, 241
Clepsine, 73, 346, 347, 349, 351, 352,
353, 354
Clio, 242, 278
Clubione, 436
Clupeidae, 64
Cobitis barbatula, 378
Coccida;, 429
Coccus, 50
Ccelebogyne, 79
Coelenterata, 3, 5, 13, 18, 26, 27, 2S, 35,
74, 93, 94, 126, 148, 170, 178,179, 1 80,
181, 191, 342
Ccenurus cerebralis, 213, 214
Coleochaete, 1 1
Coleoptera, 396, 402, 409, 412, 420, 421,
^5
Collembola, 395, 426
Comatula, 5, 552, 553
Condracanthus, ill, 120, 520
Conochilus volvox, 22 1
Convoluta, 32
Copepoda, 109, 120, 459, 460, 487, 489,
493, 496, 503, 509, 519
Corallium rubrum, 168, 182
Corethra, 422, 423, 424
Crangoninoe, 476
Crnniiuhv, 311
Craniata, 5, 6, 19, 20, 54, 56, 59, 6l, 62,
6 4 , 74, 102
Crinoidea, 35, 36, 544, 550, 568, 576
Criodilus, 321, 324, 328, 341
INDEX.
Crisia, 304
Crocodilia, 63
Crustacea, 5, 6, 18, 51, 66, 102, 109, 120,
458, 4 6 5> 487* 5<>2, 521, 524, 537, 541
Cryptophialus, 499, 509
Crystalloides, 163
Ctenophora, 26, 93, 102, 152, 173, 175,
177, 178, 179, 180, 181, 182
Ctenostomata, 292, 297, 298, 304, 305
Cucullarms elegans, 46, 75, 82, 371, 376
Cucumaria, 546, 556, 574
Cumaceae, 459, 465, 486, 506
Curculio, 421
Cyclas, 259, 260, 261, 265
Cyclops, 376, 377, 418, 489, 503
Cyclostomata, 102, -292, 304
Cymbulia, 241, 242
Cymothoa, 516, 517, 519, 520,524, 528
Cynipidae, 15, 421, 428
Cyphonautes, 297, 301, 304, 306, 308
Cypridina, 500, 502
Cysticercus cellulosce, 214, 217
,, fasciolaris, 216
,, limacis, 213
Daphnia, 79, 464
Dasychone, 331, 336
Decapoda, 66, 248, 459, 465, 469, 504,
511
Dendroccela, 32, 33, 189, 195, 196
Dentalium, 258, 576
Desmacidon, 147
Desor, type of, 196, 197, 201, 202, 204,
212, 424
Diastopora, 304
Dibranchiata, 225, 253
Dicyema, 9, 131, 134, 135, 136
Dimya, 225
Diphyes, 159
Diplozoon, 11, 209, 210
Diporpa, 210
Diptera, 49, 194, 204, 396, 401,402,407,
409, 412, 416, 420, 429
Discina radiata, 317
Discinidse, 311
Discophora, 18, 42, 165, 346, 383
Distomese, 189, 205, 425
Distomum, 31
,, cygnoides, 209
,, globiparum, 207
,, lanceolatum, 205
Dochmius duodenale, 375
,, trigonocephalus, 375
Donacia, 401
Dracunculus, 376, 377
Echinaster fallax, 23
,, Sarsii, 102, 561
Echinodermata, 5, 18, 24, 35, 74, 102,
325, 424, 544, 573, 574, 57 6 > 5 82
Echinoidea, 35, 36, 544, 549, 565, 576
Echinorhyncus, 379, 380
Echinus lividus, 83, 84, 88
Echiurus, 44 , 357, 358
Ectoprocta, 297, 306
Edriophthalmata, 459, 465
Elaphocaris, 473
Elasmobranchii, 23, 56, 59, 61, 62, 64,
67, 105, 106. 107, 108, 109
Enopla, 189, 202
Entoconcha mirabilis, 237
Entomophaga, 421
Entoprocta, 292, 298, 300, 302, 304, 306
Epeira, 436
Ephemera, 395, 409, 420, 422
Ephyra, 186
Epibulia auranliaca, 159, 165
Erichthus, 484, 507
Errantia, 319, 336
Esperia, 147
Estheria, 463, 464
Euaxes, lol, 322, 324, 341, 346,349
Eucharis, 178
,, multicornis, 178
Eucopepoda, 459
Eucope polystyla, 23, 154
Eunice sanguinea, 319
Eupagurus prideauxii, 112, 113, 115, 511,
520
Euphausia, 465, 468, 504, 505, 518, 523
Eurostomata, 176
Eurylepta auriculata, 192
Eurynome, 483
Euspongia, 146, 147
Filaria, 377
Filaridae, 371
Firoloidea, 240
Flagellata, 7, 8
Flustrella, 301, 303
Formica, 396
Fungia, 182, 186
Fusus, 275, 280, 284, 288
Gammarus, 122, 518
,, fluviatilis, 117
,, locusta, no, 112
Ganoids, 54, 102
Gasteropoda, 39, 41, 98, 225, 226, 229,
230, 232, 233, 240, 258, 260, 261, 270,
272, 275, 279, 283, 324
Gasterosteus, 64, 210
Gastrotricha, 370
Gasterotrochce, 330, 333
Gecarcinus, 465
Geophilus, 392, 393
Gephyrea, 5, 18, 24, 44, 54, 67, 102,
318, 320, 325, 355, 357, 361, 364
Germogen, 134
Geryonia hastata, 156
Geryonidse, 156
Glochidia, 267, 268
Gnathobdellidas, 346, 349
Gordiacea, 94
588
INDEX.
Cimlioidca, 371, 374, 378
;nia, 168
Gorgonidce, 181
Gorgoninrc, 181
Gregarinidae, 8
Gryllotalpa, 401, 412, 413
Gunnnineiv, 147, 148
Gymnoblastic Hydroids, 184, 185
Gymnoloemata, 292
Gymnosomata, 225, 240, 241, 242, 270
Gyrodactylus, 210
Halichondria, 147
Ilalisarca, 22, 66, 145
Halistemma, 165
Helicidce, 238
Helioporidae, 182
Helix, 67, 229
Hemiptera, 395, 402, 403, 409, 420, 421
Hessia, 108, 492
Heterakis vermicularis, .374
Heteronereis, 343
Heteropoda, 71, 72, 225, 226, 231, 278
Hexacoralla, 152, 179, 182
Hippopodius gleba, 27, 159
Hirudinea, 74, 84
Hirudo, 350, 351, 352, 353, 354
Holometabola, 420, 422
Holostomum, 205
Holothuria, 19, 25, 35, 549, 558, 576
Holothuroidea, 35, 544, 553, 556
Homarus, 477
Hyaleacea, 273, 275
Hyaleidce, 241
Hydra, 21, 22, 26, 28, 29, 34, 152, 154,
155. 179, 183
Hydractinia, 539
Hydrocoralla, 152, 181, 185
Hydroidea, 152
Hydromedusae, 152, 179, 182, 183, 184,
185, 186, 187
Hydrophilus, 374, 396, 400, 401, 402,
404, 408, 409
Hydrozoa, 14, 19, 26, 27, 67, 102, 152,
155. 165. 179, 1 80, 181, 182, 539
Ilymenoptera, 396, 401, 402, 412, 420,
421, 425
Ichneumon, 396
Inarticulata, 311, 316
Incrmi
Infusoria, 7, 8
Insecta, 5, 15, 18, 19, 25, 46, 395, 396,
4^5, 455. 45
Intoshia gigas, 136
Isidimc, 181
Ixxlyctia, 147
Isopoda, 109, 515, 519, 521, 523, 527
Julus Moneletei, 387, 388, 389
Kochlorine, 499
Lacertilia, 64
Lacinularia, 221, 223
socialis, 75
Lamellibranchiata, 23, 25, 37, 39, 98,
225, 241, 257, 258, 259, 269, 270, 271,
273, 274, 288
Lepadkue, 498
Lepas fascicularis, 224, 493, 494, 495
Lepidoptera, 79, 396, 402, 407, 408, 412,
413, 415, 417, 420, 421, 423, 415, 426.
455
Leptodora, 16, 51
Leptoplana, 74, 189, 192, 193
Lernseopoda, 490, 492, 520
Leucifer, 507
Libellulidae, 402, 403, 409, 420
Limax, 229, 232, 239, 278, 280
Limnadia, 79, 524
Limulus, 534
Lina, 402
Lingulidae, 311, 316
Lithobius, 393
Lobatse, 178
Loligo, 242, 243, 244, 247, 253
Loricata, 507, 514
Lota, 105
Loxosoma, 292, 294, 296, 306, 307
Lucernaria, 185
Lumbricus, 341, 368
,, agricola, 321
,, rubellus, 324
trapczoides, 13, 321, 323
Lumbriconereis, 334
Lymnseus, 82, 98, 226, 227, 232, 238,
281
Lycosa, 436
Macrostomum, 32, 34
Macrura, 476
Malacobdella, 203
Malacodermata, 171
Malacostraca, 66, 459, 462, 465, 504,
505, 506, 511, 523
Mammalia, 56, 58, 59, 64, 66
Marsipobranchii, 59
Mastigopus, 473, 474
Medusoe, 27, 154, 157, i.^s, 16;, 164, 176,
178, 181, 182, 183, 184, 185, 186
Megalopa, 482, 483, 484
Melolontha, 402, 421
Membranipora, 297, 303
Mermithido;, 371
Mesotrochoe, 330
Metachoetoe, 335
Metazoa, Q, 10, 12,67, 86, 125, 135, 14^,
ISO, 179
Millepora, 152, 181
Mitraria, 308, 337
Molgula, 102
Mollusca, 5, 18, 24, 66, 74, 84, 99, 225,
247, 248, 251, 256, 257, 262, 271, 285,
288, 307, 325, 333, 352, 576, 582
INDEX.
589
Monomya, -225
Monostomum capitellum, 205
,, mutabile, 205, 206
Monotrochse, 330
Montacuta, 260, 262
Musca, 396
Muscidae, 420, 423
Myobia, 444, 445
Myrianida, 343
Myriapoda, 22, iir, 113, 387, 394, 395,
4i.3 458
Mynothela, 155
Myrmeleon, 396
Mysis, 120, 469, 472, 486, 504, 509, 525
Mytilus, 260, 261
Myxinoids, 5
Myxispongise, 145
Myzostomea, 369
Nais, 342
Nassa mutabilis, 101, 226, 227, 233, 262,
278, 279, 288, 3^4
Natantia, 487
Natica, 237, 283
Nauplius, 5, 16, 460, 461, 463, 465, 466,
469, 473, 490, 491, 493, 497
Nautilus pompilius, 253, 276
Nebaliadse, 459, 465, 486
Nematoda, 45, 46, 50, 66, 74, 75, 371,
373. 374> 376
Nematogens, 131
Nematoidea, 18, 84, 94, 371, 374
Nematus ventricosus, 13, 427
Nemertea, 94, 189, 196, 202, 204
Nemertines, 30, 31, 33, 93, 136, 195,
202, 328, 333, 424
Nephelis, 82, 346, 349, 350, 351, 352,
354
Nereis, 343
,, diversicolor, 319
,, Dumerilii, 343
Neritina, 229, 237
Neuroptera, 396, 401, 420, 421
Neuroterus ventricularis, 428
Notonecta, 395
Nototrochse, 330, 353
Nudibranchiata, 229, 241
Ocellata, 184
Octocoralla, 152, 179
Octopus, 248
Odontophora, 225, 257, 271
Odontosyllis, 333
Oedogonium, 1 1
Oligochseta, 42, 319, 321, 325, 330, 338,
346, 352
Olynthus, 144
Oniscus murarius, 107, 108, 109, 120,
516, 520, 528
Opercula, 31
Ophiothryx, 36, 549
Ophidia, 64
Ophiuroidea, 136, 544, 553, 562, 565,
576
Ophryotrochoe puerilis, 333
Opisthobranchiata, 225, 232, 237
Ornithodelphia, 109
Orthonectidae, 136
Orthoptera, 395, 414, 420, 421, 425, 426
Ostracoda, 459, 500, 510
Ostrea, 259, 260, 262
Oxyuridse, 46, 373, 374
Oxyurus ambigua, 374
,, vermicularis, 375
PcEcilopoda, 534
Paguridse, 477
Pakemon, no
Palaemonetes, 476
Pakemoninre, 476, 511, 512
Palinurus, 478, 480
Paludina, 66, 227, 229, 235, 270, 278,
280
,, costata, 229
,, vivipara, 226
Pandorina, n
Parasita, 489
Pedalion, 221
Pedicellina, 98, 292, 296, 299, 307
Pelagia, 167, 185
Penseinse, 476
Penaeus, no, 113, 465, 469, 473, 474,
504, 518
Pennatulidae, 181
Pentacrinus, 5
Pentastomida, 539, 540
Pentastomum denticulatum, 540, 54!
tsenoicles, 539, 540, 541
Percidae, 64
PerennichaetcE, 335
Peripatus, 5, 386, 411, 412, 413, 542
Petromyzon, 61, 63, 64, 74, 83
Phalangella, 304
Phalangidse, 436
Phallusia, 83
Phascolosoma, 44, 355, 356, 361
Pholcus, 436, 442
Phoronis, 315, 355, 363, 364
Phoxinus laevis, 378
Phryganea, 396, 401, 409
Phylactokemata, 292, 294, 297, 305, 306
Phyllobothrium, 218
Phyllodoce, 329
Phyllopoda, 16, 459, 461, 505
Phyllosoma, 479, 480
Phylloxera, 429
Physophoridoe, 152, 16-2, 164
Pilidium, type of, 196, 200, 201, 202, 704,
424
Pisces, 5
Piscicola, 20, 43
Pisidium, 259, 260, 262, 264
Planaria Neapolitana, 193
Planorbis, 273, 281, 325
590
INDEX.
Platyelminthes, 18, 20, 24, 221, 424
Platygaster, 396, 416, 417, 418, 419
Pleurohrachia, 176, 177, 238
Pneumodermon, 242, 576
Podostomata, 292
Poduridce, 401, 405
Polychaeta, 42, 319, 325, 338
Polydesmus complanatus, 387, 388
Polygordius, 319, 325, 326, 327, 328,
332, 357 386
Polynoe, 42, 331
Polyophthalmus, 328
Polyplacophora, 225, 254, 270, 271, 288
Polystomeas, 189, 205, 209
Polystomum, 209
,, integerrimum, 30, 31, 210
Polytrochne, 330, 333
Polyxenia leucostyla, 158
Polyxenus lagurus, 387
Polyzoa, 98, 303, 305, 306. 30 8 > 3 ! 5. 3^
Porcellana, 483
Porifera, 102, 138, 148
Porthesia, 115
Prorhyncus, 32, 34
Prosobranchiata, 225, 237, 281
Prostomum, 32, 34, 38, 196
Protozoa, 8, 9, lo, n, 86, 135, 149
Protozoaea, 471
Protula Dysteri, 342
Pseudoneuroptera, 426
Pseudoscorpionid;e, 434
Psolinus, 556, 574
Psychidae, 16
Pteraster miliaris, 561
Pteropoda, 98, 225, 226, 229, 230, 232,
240, 258, 270, 272, 279, 283
Pterotrachcea, 71, 229, 240
Pulex, 396
Pulmonata, 39, 225, 232, 238, 281, 282
I'urpura lapillus, 78
Pycnogonida, 538
Pyrosoma, 13, 53, 109
Rana temporaria, 210
Kaspailia, 147
Rcdia, 206, 207, 208, 209
Reniera, 147
Kcptilia, 56, 59, 60, 61, 62, 64, 109
Rhabditis dolichura, 82
Khabdoccela, 32, 33, iSy, ic/>
Khnbdopleura, 294, 306
Rhi/occphala, 459, 493, 499, 500
Klii/.ocrinus, 5
klii/.ostoma, 167
Rhomlx>gens, 131, 134
Khynchoncllidaj, 311
Rhyncdbddlkbe, 346
Rotifera, 5, 12, 18, 75, 76, 77, 79, 83,
102, 221, 308, 325
Saccocirrus, 328, 329, 332, 340
Sacculina, 500
Sagartia, 169, 171
Sagitta, 33, 74, 94, 130, 366, 367, 368
Salmonidrc, 64
Salpa, 102
Sarcia, 164
Seaphopoda, 225, 257, 270, 271
Schistocephalus, 2 1 1
Schizopoda, 459, 465, 466
Scolopendra, 392
Scorpio, 120, 43 r, 44 6, 454, 455, 457
Scrobicularia, 38, 39
Scyllarus, 477
Scyphistoma, 179, 185, 186
Sedentaria, 319, 336
Sepia, 20, 40, 41, 242, 243, 244, 245,
247> 2 49> 253
Sergestidce, 473, 507
Serpula, 319. 325, 331
Sertularia, 152, 183, 184
Silicispongia.', 147
Simulia, 401, 415
Siphonophora, 13, 77, 152, 159, 163,
165, 179, 1 80, 182, 185
Sipunculida, 24
Sipunculus, 44
Sirex, 396
Sitaris, 42!
Spathegaster baccarum, 428
Spjo, 4 2 > 33 2 > 333
Spiroptera obtusa, 376
Spirorbis Pagenstecheri, 319
spirillum, 319, 336
Spirula, 252
Spirulirostra, 252
Spongelia, 147
Spongida, 138, 144, 148, 149
Spongilla, 147, 150
Sporocysts, 206, 207, 208, 209
Squilla, 66, 504, 507
Stephanomia pictum, 162, 165
Stomalopoda, 459, 465, 4X4
Stomodoeum, 413
Strongylidrc, 371, 375
Strongylocentrus, 567
Strongysoloma Guerinii, 3<S7, 388, 390
Stylasterictae, 152, r8r
Styliolidic, 24!
Stylochopsis ponticus, 193
Sycandra, 93, 138, 144, 145, 147, 150
,, raphanus, i^S, 174
Syllis, 343
vivipara, 319
Sympodium coralloidcs, 168
Taeniatoe, 178
Tardigrada, 541
Teoenaria, 436
'I'clcDsti'i, IS, 25, 5^), 59, C>4. 107, io<)
I'r].)troch;i.-, 330
Tcndra, 300
'I '(.'nth reds, 396
Tcrcbdla concliilcga, 332, 333, 337
INDEX.
591
Terebella nebulosa, 332, 333
Terebratula, 311, 315
Terebratulina, 311, 315, 316
,, septentrionalis, 315, 316
Teredo, larva of, 262
Tergipes, 232, 238
,, Edwardsii, 238
,, lacinulatus, 238
Tethya, 147
Tetrabranchiata, 225
Tetranychus telarius, 116
Tetrastemma varicolor, 203
Thalassema, 44, 355, 357
Thalassinidae, 477
Thallophytes, n
Thecidium, 311, 312, 315, 316
Thecosomata, 225
Thoracica, 459, 493, 499, 500
Thysanozoon, 192, 193
Thysanura, 395, 408, 425, 458
Tichogonia, 39
Tipula, 396
Tipulidae, 420, 421
Toenia cosnurus, 214
,, echinococcus, 215, 217
solium, 217
Tornaria, 579, 581
Toxopneustes, 22, 24, 35, 85, 88, 89
Tracheata, 385, 426, 432, 44 8, 455, 457,
458, 538, 54i
Trachymedusae, 152, 156, 179, 185
Trematodes, 14, 16, 29, 30, 31, 32, 33,
46, 94, 189, 205, 208, 210, 212, 216
Trichina, 377, 378
Trichinidse, 371
Trichocepha'lus affinis, 374
Trochosphsera aequatorialis, 221
TubiporidcE, 182
Tubularia, 34, 38, 152, 154, 158
Tubularidse, 29, 179, 183
Tunicata, 5, I 4 , 53
Turbellaria, 5, 30, 31, 33, 74, 98, 102,
136, 179, 189, 193, 333
Tyroglyphus, 445
Unio, 37, 38, 39, 100, 101, 259, 260,265,
266, 445
Vaginulus luzonicus, 229
Vermes, 5, 74, 102, 223, 324, 352
Verongia rosea, 146
Vertebrata, 14, 18, 19, 24, 59, 64, 83,
272, 349. 397' 4^6
Vesiculata, 184
Vitrina, 229
Vorticella, 8, 9, 10
Wilsia, 164
Xiphoteuthis, 252
Zoantharia, 152, 168, 169
Zooea, 465, 468, 471, 474, 482, 483, 484,
486, 504
BIBLIOGRAPHY.
THE OVUM.
General Works.
(1) } Ed. van Beneden. "Recherches sur la composition et la signification de
,A T m ' cour ' d ' l Acad " r y- des Sci <<* de Belgique, Vol. xxxiv. 1870.
/ '%, R- Leuckart. Artikel "Zeugung," R. WagMsfs Handworterbtek d. Physio
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(5) AllenThomson. Article ' ' Ovum " in Todd's Cyclopedia of Anatomy and
Physiology, Vol. v. 1859.
(6) W. Waldeyer. Eierstock u. EL Leipzig, 1870.
THE OVUM OF CCELENTERATA.
(7) Ed. van Beneden. "De la distinction originelle d. testicule et de
1'ovaire." Bull. Acad. roy. Belgique, f serie, Vol. xxxvu. 1874.
(8) R. and O. Hertwig. Der Organismus d. Medusen. Jena, 1878.
(9) N. Kleinenberg. Hydra. Leipzig, 1872.
THE OVUM OF PLATYELMINTHES.
(10) P. Hallez. Contributions a fHistoire naturelle des Turbellarih. Lille,
1879.
(11) S. MaxSchultze. Beitrdge z. Naturgeschichte d. Turbellarien. Greifswald, 1851.
(12) C. Th. von Siebold. ' ' Helminthologische Beitrage." Miiller's Archiv,
1836.
(13) C. Th. von Siebold. Lehrbuch d. vergleich. Anat.d. wirbellosen Thiere.
Berlin, 1848.
(14) E. Zeller. " Weitere Beitrage z. Kenntniss d. Polystomen." Zeit. f.
wiss. ZooL, Bd. xxvu. 1876.
[Vide also Ed. van Beneden (No. i).]
THE OVUM OF ECHINODERMATA.
(15) C. K. Hoffmann. " Zur Anatomic d. Echiniden u. Spatangen." Niederllindisch. Archiv f. Zoologie, Vol. I. 1871.
(16) C. K. Hoffmann. " Zur Anatomic d. Asteriden. Niederldndisch. Ardiiv
/. Zoologie, Vol. n. 1873.
(17) H. Ludwig. "Beitrage zur Anat. d. Crinoiden." Zeil. f. wiss. Zool.,
Vol. xxvin. 1877.
(18) Job. Miiller. "Ueber d. Canal in d. Eiern d. Holothurien." Miiller's
Archiv, 1854.
(19) C. Semper. Holothurien. Leipzig, 1868.
(20) E. Selenka. Befruchtung d. Eies v. Toxopneustes variegalits, 1878.
[Vide also Ludwig (No. 4), etc.]
1 A very complete and critical account of the literature is contained in this paper.
B. II. a
BIBLIOGRAPHY.
THE OVUM OF MOLLUSC A.
Lamellibranchiata.
(21) II. Lacaze-Duthiers. " Organes genitaux des Acephales Lamellibranches." Ann. Set. Nat., 4 mc serie, Vol. 1 1. 1854.
(22) W. F lemming. " Ueb. d. er. Entwick. am Ei d. Teichmuschel." Archiv
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(23) W. Flamming. "Studien lib. d. Entwick. d. Najaden." Sitz. d. t: Akad.
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(24) Th. von Hassling. " Einige Bemerkungen, etc." Zeit. f. wiss. ZooL,
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f. wiss. ZooL, Vol. xxix. 1877.
(26) Keber. De Introihi Spermatozoorum in ovula, etc. Konigsberg, 1853.
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(28) C. Semper. "Beitrage z. Anat. u. Physiol. d. Pulmonaten." Zeit. f.
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ZooL, Vol. xix. 1869.
(30) Fr. Leydig. " Ueb. Paludina vivipara." Zeit.f. wiss. ZooL, Vol. u. 1850.
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(31) Al. Kolliker. Entwicklungsgeschichte d. Cephalopoden. Zurich, 1844.
(32) E. R. Lankester. "On the Developmental History of the Mollusca."
Phil. Trans., 1875.
THE OVUM OF THE CHJETOPODA.
(33) Ed. Claparede. " Les Annelides Chaetopodes d. Golfe de Naples."
Mem.d. 1. Soctit. phys. eld 1 hist. nat. de Geneve, 1868 9 and 1870.
(34) E. Ehlers. Die Borstcnwiirmer nach system, und anat. Untersuchungen.
Leipzig, 186468.
(35) E. Selenka. " Das Gefass-System d. Aphrodite aculeata." Niedcrldndisches Archiv f. ZooL, Vol. n. 1873.
THE OVUM OF DISCOPHORA.
(36) H. Dorner. " Ueber d. Gattung Branchiobdella." Zeit.f. wiss. ZooL,
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(37) R. Leuckart. Die menschlichen Parasiten.
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(30) C. O. Whitman. "Embryology of Clepsine." Quart. 7. of Alter.
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THE OVUM OF GEPHYREA.
(40) Keferstein u. Ehlers. Zoologische Beitrage. Leipzig, 1861.
(41) C. Semper. Holothurien, 1868, p. 145.
(42) J. W. Spengel. " Beitrage z. Kenntniss d Gephyreen." Beitriigc a. d.
zool. Stationz. Neapcl, Vol. I. 1879.
(43) J. W. Spengel. " Anatomische Mittheilungen lib. Gephyreen." Tagcbl.
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THE OVUM OF NEMATODA.
(44) Ed. Claparede. De la formation ct de la fccondaiiou dcs- n-uf.\ chcz Ics
I'crs Ntmatodcs. (ienevc, 1859.
(J- r )) K. I. (.-nek art. Hif nirnsf/i lichen Paras! ten.
BIBLIOGRAPHY. jjj
d.Nematoden."
^' Nels0n * " On the reproduction of Ascaris mystax, etc." Phil.
(48) A.Schneider. Monographie d.' Nematoden. Berlin, 1866.
THE OVUM OF INSECT A.
Sm ' T? r u n d V Ueb ,?'* a5 Ei u ' seine Bildungsstdtte. Leipzig, 1 878.
(50) T. H. Huxley. " On the agamic reproduction and morphology of Aphis.
Ltnnean Trans., Vol. xxn. 1858. Vide also Manual of Invertebrate* Animals, 1877.
1 * ^ ^ ^ *
(51)
bei den *,++,*
/-a\ ? r ',k ey< MS' Der Eierstock u. die Samentasche d. Insecten. Dresden, 1866.
tSl ~ ub . bock - " The ov a and pseudova of Insects." Phil. Trans. 1850.
(o4) Stem. Die weiblichen Geschlcchtsorgane d. Ktifer. Berlin, 1847.
[Conf. also Glaus, Landois, Weismann, Ludwig (No. 4).]
THE OVUM OF ARANEINA.
(55) Victor Cams. " Ueb. d. Entwick. d. Spinneneies." Zeit. f. wiss. Zool. t
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[Conf. Leydig, Balbiani, Ludwig (No. 4), etc.]
THE OVUM OF CRUSTACEA.
(57) Aug. Weismann. "Ueb. d. Bildung von Wintereiern bei Leptodora
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THE OVUM OF CHORD ATA.
Urochorda (Tunicata).
(58) A. Kowalevsky. " Weitere Studien ii. d. Entwicklung d. Ascidien."
Archiv f. micr. Anat., Vol. VII. 1871.
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Arch.f. micr. Anat., Vol. xi. 1875.
(60) Kupffer. " Stammverwandtschaft zwischen Ascidien u. Wirbelthieren."
Arch. f. micr. Anat., Vol. VI. 1870.
(61) Giard. " Etudes critiques des travaux, etc. " Archives Zool. experiment.,
Vol. I. 1872.
(62) C. Semper. " Ueber die Entstehung, etc." Arbeiten a. d. zool.-zoot.
Institut Wiirzburg, Bd. II. 1875.
Cephalochorda.
(63) P. Langerhans. "Z. Anatomic d. Amphioxus lanceolatus," pp. 330 3.
Archiv f. mikr. Anat., Vol. xil. 1876.
Craniata.
(64) F. M. Balfour. "On the structure and development of the Vertebrate
Ovary." Quart. J. of Micr. Science, Vol. xvm. 1878.
(65) Th. Eimer. " Untersuchungen ii. d. Eier d. Reptilien." Arckiv f.
mikr. Anat., Vol. vni. 1872.
(66) Pfliiger. Die Eierstbcke d. Sdugethiere u. d. Menschen. Leipzig, 1863.
(67) J. Foulis. " On the development of the ova and structure of the ovary in
Man and other Mammalia." Quart. J. of Micr. Science, Vol. XVI. 1876.
(68) J. Foulis. " The development of the ova, etc." Journal of Anat. and
Phys., Vol. xni. 18789.
a 2
IV BIBLIOGRAPHY.
(69) C. Gegenbaur. " Ueb. d. Bau u. d. Entwicklung d. Wirbelthiereier mit
partieller Dottertheilung." Muller's Archiv, 1861.
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(71) W. His. Untersuchungen iib. d. Ei u. d. Eientwicklung bei Knochenfischcn.
Leipzig, 1873.
(72) A. Kolliker. Entwicklungsgeschichte d. Menschen u. hoherer Thicre,
Leipzig, 1878.
(73) J. Miiller. " Ueber d. zahlreichen Porenkanale in d. Eikapsel d. Fische."
Muller's Archiv, 1854.
(74) W. H. Ransom. " On the impregnation of the ovum in the Stickleback."
Pro. K. Society, Vol. vn. 1854.
(75) C. Semper. " Das Urogenitalsystem d. Plagiostomen etc." Arbeiten a.
d. zool.-zoot. Instit. Wiirzburg, Vol. II. 1875.
[Cf. Ludwig, No. 4, Ed. van Beneden, No. i, Waldeyer, No. 6, etc.]
MATURATION AND IMPREGNATION OF THE OVUM.
(76) Auerbach. Organologische Studien, Heft 2. Breslau, 1874.
(77) Bambeke. " Recherches s. Embryologie des Batraciens." Bull, de
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BIBLIOGRAPHY.
DIVISION OF NUCLEUS.
(101) W. Flamming. "Beitrage z. Kenntniss d. Xclle u. ihrcr Lcbun.scrschcinungen." Archiv f. mikr. Anat., Vol. xvi. 1878.
(102) E. Klein. "Observations on the glandular epithelium and division of
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(103) Peremeschko. "Ueber d. Theilung d. thierischen Zellen." Archiv f.
mikr. Anat., Vol. xvi. 1878.
(104) E. Strasburger. "Ueber ein z. Demonstration geeignetes ZclltheilungsObject." Sitz. d. Jenaischen Gesell.f. Med. u. Naturwiss., July 18, 1879.
SEGMENTATION.
(105) E. Haeckel. "Die Gastrula u. Eifurchung." Jenaische Ztitschrift, Vol.
ix. 1877.
(106) Fr. Leydig. "Die Dotterfurchung nach ihrem Vorkommen in d. Thierwelt u. n. ihrer Bedeutung." Oken. /sis, 1848.
GENERAL WORKS ON EMBRYOLOGY.
(107) K. E. von Baer. " Ueb. Entwicklungsgeschichte d. Thiere." Konigsberg, 182837.
(108) C. Glaus. Grundziige d. Zoologie. Marburg und Leipzig, 1879.
(109) C. Gegenbaur. Grundriss d. vergleichenden Anatomie. Leipzig, 1878.
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1878.
(110) E. Haeckel. Studien z. Gastrcea-Theorie. Jena, 1877, and also Jenaische Zeitschrift, Vols. vni. and ix.
(111) E. Haeckel. Schopfungsgeschichte. Leipzig. Vide also Translation.
The History of Creation. King and Co., London, 1876.
(112) E. Haeckel. Anthropogenie. Leipzig. Vide also Translation. Anthropogeny (Translation). Kegan Paul and Co., London, 1878.
(113) Th. H.Huxley. The Anatomy of Invertebrated Animals. Churchill,
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(114) E. R. Lankester. "Notes on Embryology and Classification." Quart.
J. of Micr. Science, Vol. xvi I. 1877.
(115) A. S. P. Packard. Life Histories of Animals, including Man, or Outlines
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(116) H. Rathke. Abhandlungen z. Bildung- und Entwicklungsgesch. d. Menschen u. d. Thiere. Leipzig, 1833.
DICYEMID.E.
(117) E van Beneden. "Recherches sur les Dicyemides." Bull. d. FAcadtmie roy. de Belgique, f ser. T. XLI. No. 6 and T. XLII. No. 7, 1876. Vide this
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(118) A. K 611 ike r. Ueber Dicyema paradoxum den Schmarotzer der Venenanhiinge der Cephalopoden. ,
(119) Aug. Krohn. "Ueb. d. Vorkommen von Entozoen, etc. Fronep
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ORTHONECTID^E.
(120) A If. Giard. "Les Orthonectida classe nouv. d. Phylum des Vers."
journal de tAnat. et de la Physiol., Vol. XV. 1879.
(121) El. Metschnikoff. "Zur Naturgeschichte d. OrthonecUdae." Zoologi
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PORIFERA.
'(122) C Barrois. " Embryologie de quelques eponges de la Manche. " An
""$) & &ZS^^'<t*>* SP"6es." A~* ^ M g . cf
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vi BIBLIOGRAPHY.
(124) Ganin 1 . " Zur Entwicklung d. Spongilla fluviatilis." Zoologischer Anzeigtr, Vol. i. No. 9, 1878.
(125) Robert Grant. "Observations and Experiments on the Structure and
Functions of the Sponge." Edinburgh Phil. jf., Vol. xm. and XIV., 1825, 1816.
(126) E. Haeckel. Die Kalkschwamme, 1872.
(127) E. Haeckel. Studien zur Gastraa- Theorie. Jena, 1877.
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POLYZOA.
General.
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GEPHYREA.
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CAMBRIDGE : PRINTKD BY C. J. CLAY, M.A. & SON, AT THE UNIVERSITY PRtSS.
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Foster M. and Sedgwick A. The Works of Francis Balfour Vol. II. A Treatise on Comparative Embryology 1. (1885) MacMillan and Co., London.

The Ovum and Spermatozoon | The Maturation and Impregnation of the Ovum | The Segmentation of the Ovum | Dicyemae and Orthonectidae Dicyema | Porifera | Coelenterata | Platyhelminthes | Rotifera | Mollusca | Polyzoa | Brachiopoda | Chilopoda | Discophora | Gephyrea | Chaetognatha | Nemathelminthes | Tracheata | Crustacea | Pcecilopoda | Echinodermata | Enteropneusta | Bibliography
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This historic 1885 book edited by Foster and Sedgwick is the second of Francis Balfour's collected works published in four editions. Francis (Frank) Maitland Balfour, known as F. M. Balfour, (November 10, 1851 - July 19, 1882) was a British biologist who co-authored embryology textbooks.



The Works of Francis Balfour Foster M. and Sedgwick A. The Works of Francis Balfour Vol. I. Separate Memoirs (1885) MacMillan and Co., London.

Foster M. and Sedgwick A. The Works of Francis Balfour Vol. II. A Treatise on Comparative Embryology 1. (1885) MacMillan and Co., London.

Foster M. and Sedgwick A. The Works of Francis Balfour Vol. III. A Treatise on Comparative Embryology 2 (1885) MacMillan and Co., London.

Foster M. and Sedgwick A. The Works of Francis Balfour Vol. IV. Plates (1885) MacMillan and Co., London.

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Vol II. A Treatise on Comparative Embryology (1885)

CHAPTER XVIII CRUSTACEA

History of the larval forms 1 '.

THE larval forms of the Crustacea appear to have more faithfully preserved their primitive characters than those of almost any other group.

BRANCHIOPODA.

The Branchiopoda, comprising under that term the Phyllopoda and Cladocera, contain the Crustacea with the maximum number of segments and the least differentiation of the separate appendages. This and other considerations render it probable that they are to be regarded as the most central group of the Crustaceans, and as in many respects least modified from the ancestral type from which all the groups have originated.

1 The following is the classification of the Crustacea employed in the present chapter.

i Phyllopoda. ( Natantia.

I. Branchiopoda. ciadocenu III. Copepoda. Euc P e P da Iparasita.

( Branchiura T Nebaliadse. jThoracica.

M f Sat- < v - wdi, p a minai ia

II. Malacostraca. ] Stomatopoda . ULocephaia.

I Cumacese. v. Ostracoda.

I Edriophthalmata.

2 The importance of the larval history of the Crustacea, coupled with our comparative ignorance of the formation of the layers, has rendered it necessary for me to diverge somewhat from the general plan of the work, and to defer the account of the formation of the layers till after that of the larval forms.

The free larval stages when such exist commence with a larval form known as the Nauplius.

The term Nauplius was applied by O. F. Muller to certain larval forms of the Copepoda (fig. 229) in the belief that they were adult.


FlG. 208. TWO STAGES IN THE DEVELOPMENT OF APUS CANCRIFORM1S.

(After Claus.)

A. Nauplius stage at the time of hatching.

B. Stage after first ecdysis.

an 1 , and a 2 . First and second antennae ; md. mandible ; MX. maxilla ; /. labrum; fr. frontal sense organ ; /. caudal fork ; s. segments.

The term has now been extended to a very large number of larvae which have certain definite characters in common. They are provided (fig. 208 A) with three pairs of appendages, the future two pairs of antennae and mandibles. The first pair of antennae (an 1 ) is uniramous and mainly sensory in function, the second pair of antennae (an*) and mandibles (md) are biramous swimming appendages, and the mandibles are without the future cutting blade. The Nauplius mandibles represent in fact the palp. The two posterior appendages are both provided with hook-like prominences on their basal joints, used in mastication. The body in most cases is unsegmented, and bears anteriorly a single median eye. There is a large upper lip, and an alimentary canal formed of cesophagus, stomach and rectum. The anus opens near the hind end of the body. On the dorsal surface small folds of skin frequently represent the commencement of a dorsal shield. One very striking peculiarity of the Nauplius according to Claus and Dohrn is the fact that the second pair of antennae is innervated from a sub-oesophageal ganglion. A larval form with the above characters occurs with more or less frequency in all the Crustacean groups. In most instances it does not exactly conform to the above type, and the divergences are more considerable in the Phyllopods than in most other groups. Its characters in each case are described in the sequel. Phyllopoda. For the Phyllopoda the development of Apus cancriformis may conveniently be taken as type (Claus, No. 454). The embryo at the time it leaves the egg (fig. 208 A) is somewhat oval in outline, and narrowed posteriorly. There is a slight V-shaped indentation behind, at the apex of which is situated the anus. The body, unlike that of the typical Nauplius, is already divided into two regions, a cephalic and post-cephalic. On the ventral side of the cephalic region there are present the three normal pairs of appendages. Foremost there are the small anterior antennae (an 1 ), which are simple unjointed rod-like bodies with two moveable hairs at their extremities. They are inserted at the sides of the large upperlip or labrum (/). Behind these are the posterior antennae, which are enormously developed and serve as the most important larval organs of locomotion. They are biramous, being formed of a basal portion with a strong hook-like bristle projecting from its inner side, an inner unjointed branch with three bristles, and an outer large imperfectly five-jointed branch with five long lateral bristles. The hook-like organ attached to this pair of appendages would seem to imply that it served in some ancestral form as jaws (Claus). This character is apparently universal in the embryos of true Phyllopods, and constantly occurs in the Copepoda, etc.

The third pair of appendages or mandibles (md) is attached close below the upper lip. They are as yet unprovided with cutting blades, and terminate in two short branches, the inner with two and the outer with three bristles.

At the front of the head there is the typical unpaired eye. On the dorsal surface there is already present a rudiment of the cephalic shield, continuous anteriorly with the labrum (/) or upper lip, the extraordinary size of which is characteristic of the larvae of Phyllopods. The post-cephalic region, which afterwards becomes the thorax and abdomen, contains underneath the skin rudiments of the five anterior thoracic segments and their appendages, and presents in this respect an important variation from the typical Nauplius form. After the first ecdysis the larva (fig. 208 B) loses its oval form, mainly owing to the elongation of the hinder part of the body and the lateral extension of the cephalic shield, which moreover now completely covers over the head and has begun to grow backwards so as to cover over the thoracic region. At the second ecdysis there appears at its side a rudimentary shell gland. In the cephalic region two small papillae (fr) are now present at the front of the head close to the unpaired eye. They are of the nature of sense organs, and may be called the frontal sense papillae. They have been shewn by Claus to be of some phylogenetic importance. The three pairs of Nauplius appendages have not altered much, but a rudimentary cutting blade has grown out from the basal joint of the mandible. A gland opening at the base of the antennae is now present, which is probably equivalent to the green gland often present in the Malacostraca. Behind the mandibles a pair of simple processes has appeared, which forms the rudiment of the first pair of maxillae (mx).

In the thoracic region more segments have been added posteriorly, and the appendages of the three anterior segments are very distinctly formed. The tail is distinctly forked. The heart is formed at the second ecdysis, and then extends to the sixth thoracic segment : the posterior chambers are successively added from before backwards.

At the successive ecdyses which the larva undergoes new segments continue to be formed at the posterior end of the body, and limbs arise on the segments already formed. These limbs probably represent the primitive form of an important type of Crustacean appendage, which is of value for interpreting the parts of the various malacostracan appendages. They consist (fig. 209) of a basal portion (protopodite of Huxley) bearing two rami. The basal portion has two projections on the inner side. To the outer side of the basal portion there is attached a dorsally directed branchial sack (br) (epipodite of Huxley). The outer ramus (ex) (exopodite of Huxley) is formed of a single plate with marginal setae. The inner one (en) (endopodite of Huxley) is four-jointed, and a process similar to those of the basal joint is given off from the inner side of the three proximal joints.

At the third ecdysis several new features appear in the cephalic region, which becomes more prominent in the succeeding stages. In the first place the paired eyes are formed at each side

of and behind the unpaired eye, second ly the posterior pair of maxillae is formed though it always remains very rudimentary. The shell gland becomes fully developed opening at the base of the first pair of maxillae. The dorsal shield gradually grows backwards till it covers its full complement of segments.


After the fifth ecdysis the Nauplius

FIG. 209. TYPICAL PHYLLOPOD APPENDAGE. (Copied appendages undergo a rapid atrophy. f rom ciaus.)

The second pair of antennae especially ex. exopodite ; en. endo becomes reduced in size, and the man


dibular palp the primitive Nauplius portion bearing the two proxir . ..... , mal projections is not sharply

portion of the mandible is contracted separated from the endopoto a mere rudiment, which eventually dite completely disappears, while the blade is correspondingly enlarged and also becomes toothed. The adult condition is only gradually attained after a very large number of successive changes of skin.

The chief point of interest in the above development is the fact of the primitive Nauplius form becoming gradually converted without any special metamorphosis into the adult condition 1 .

Branchipus like Apus is hatched as a somewhat modified Nauplius, which however differs from that of Apus in the hinder region of the body having no indications of segments. It goes through a very similar metamorphosis, but is at no period of its metamorphosis provided with a dorsal shield : the second pair of antennae does not abort, and in the male is provided with clasping organs, which are perhaps remnants of the embryonic hooks so characteristic of this pair of antennas.

The larva of Estheria when hatched has a Nauplius form, a large upper lip, caudal fork and single eye. There are two functional pairs of swimming appendages the second pair of antennae and mandibles. The first pair of antennae has not been detected, and a dorsal mantle to form the shell is not developed. At the first moult the anterior pair of antennae arises as small stump-like structures, and a small dorsal shield is also formed. Rudiments of six or seven pairs of appendages sprout

1 Nothing appears to be known with reference to the manner in which it comes about that more than one appendage is borne on each of the segments from the eleventh to the twentieth. An investigation of this point would be of some interest with reference to the meaning of segmentation out in the usual way, and continue to increase in number at successive moults : the shell is rapidly developed. The chief point of interest in the development of this form is the close resemblance of the young larva to a typical adult Cladocera (Claus). This is shewn in the form of the shell, which has not reached its full anterior extension, the rudimentary anterior antennae, the large locomotor second pair of antennas, which differ however from the corresponding organs in the Cladocera in the presence of typical larval hooks. Even the abdomen resembles that of Daphnia. These features perhaps indicate that the Cladocera are to be derived from some Phyllopod form like Estheria by a process of retrogressive metamorphosis. The posterior antennas in the adult Estheria are large biramous appendages, and are used for swimming ; and though they have lost the embryonic hook, they still retain to a larger extent than in other Phyllopod families their Nauplius characteristics.

The Nauplius form of the Phyllopods is marked by several definite peculiarities. Its body is distinctly divided into a cephalic and post-cephalic region. The upper lip is extraordinarily large, relatively very much more so than at the later stages. The first pair of antennae is usually rudimentary and sometimes even absent ; while the second pair is exceptionally large, and would seem to be capable of functioning not only as a swimming organ, but even as a masticating organ. A dorsal shield is nearly or quite absent.

Cladocera. The probable derivation of the Cladocera from a form similar to Estheria has already been mentioned, and it might have been anticipated that the development would be similar to that of the Phyllopods. The development of the majority of the Cladocera takes place however in the egg, and the young when hatched closely resembles their parents, though in the egg they pass through a Nauplius stage (Dohrn). An exception to the general rule is however offered by the case of the winter eggs of Leptodora, one of the most primitive of the Cladoceran



families. The summer eggs after Sars.)


FIG. 709 A. NAUPLIUS LARVA OF LEPTODORA IIYAI.INA FROM wiNTKR EGG. (Copied from Bronn ;


develop without metamor


/'. antenna of first pair; an*, antenna of


phosis, but Sars (No. 461) second pair; ntd. mandible;/ caudal fork.


has discovered that the larva leaves the winter eggs in the form of a Nauplius (fig. 209). This Nauplius closely resembles that of the Phyllopods. The body is elongated and in addition to normal Nauplius appendages is marked by six pairs of ridges the indications of the future feet. The anterior antennae are as usual small ; the second large and biramous, but the masticatory bristle characteristic of the Phyllopods is not present. The mandibles are without a cutting blade. A large upper lip and unpaired eye are present.

The adult form is attained in the same manner as amongst the Phyllopods after the third moult.


MALACOSTRACA.

Owing to the size and importance of the various forms included in the Malacostraca, greater attention has been paid to their embryology than to that of any other division of the Crustacea ; and the proper interpretation of their larval forms involves some of the most interesting problems in the whole range of Embryology.

The majority of Malacostraca pass through a more or less complicated metamorphosis, though in the Nebaliadae, the Cumaceae, some of the Schizopoda, a few Decapoda (Astacus, Gecarcinus, etc.), and in the Edriophthalmata, the larva on leaving the egg has nearly the form of the adult. In contradistinction to the lower groups of Crustacea the Nauplius form of larva is rare, though it occurs in the case of one of the Schizopods (Euphausia, fig. 212), in some of the lower forms of the Decapods (Penaeus, fig. 214), and perhaps also, though this has not been made out, in some of the Stomatopoda.

In the majority of the Decapoda the larva leaves the egg in a form known as the Zoaea (fig. 210). This larval form is characterised by the presence of a large cephalo thoracic t shield usually FIG. 210. ZO^EAOFTHIAPOLITA. (After'Claus.) , ., , , , , mxp*. second maxillipede.

armed with lateral, anterior, and dorsal spines. The caudal segments are well de B. II. 30



466 SCHIZOPODA.


veloped, though wit/tout appendages, and the tail, which functions in swimming, is usually forked. The six posterior thoracic segments are, on the other hand, rudimentary or non-existent. There are seven anterior pairs of appendages shewn in detail in fig. 21 1, viz. the two pairs of antennae (At. I. and At. II.), neither of them used as swimming organs, the mandibles without a palp (ma 7 ), well-developed maxillae (two pairs, mx I and mx 2), and two or sometimes (Macrura) three pairs of biramous natatory maxillipeds (mxp I and mxp 2). Two lateral compound stalked eyes are present, together with a median Nauplius eye. The heart has in the majority of cases only one or two (Brachyura) pairs of ostia.

The Zoaea larva, though typically developed in the Decapoda, is not always present (e.g. Astacus and Homarus), and some


FIG. 211. THE APPENDAGES OF A CRAB Z<VEA.

.-//./. first antenna ; At. I I. second antenna ; md. mandible (without a palp); mx. \. first maxilla; mx. i. second maxilla; mxp. \. first maxilliped ; mxp. i. second maxilliped.

ex. exopodite ; en. endopodite.

times occurs in a very modified form. It makes its appearance in an altered garb in the ontogeny of some of the other groups.

The two Malacostracan forms, amongst those so far studied, in which the phylogenetic record is most fully preserved in the ontogeny, are Euphausia amongst the Schizopods and Penaeus amongst the Decapods.

Schizopoda. Euphausia leaves the egg (MetschnikofT, No. 4689) as a true Nauplius with only three pairs of appendages, the two hinder


CRUSTACEA.


467


biramous, and an unsegmented body. The second pair of antennae has not however the colossal dimensions so common in the lower types. A mouth is present, but the anus is undeveloped.

After the first moult three pairs of prominences the rudiments of the two maxillae and ist maxillipeds arise behind the Nauplius appendages (fig. 212). At the same time an anus appears between the two limbs of a rudimentary caudal fork ; and an unpaired eye and upper lip appear in front. After another moult (fig. 212) a lower lip is formed (UL) as a pair of prominences very similar to true appendages ; and a delicate cephalo-thoracic shield also becomes developed. Still later the cutting blade of the mandible is formed, and the palp (Nauplius appendage) is greatly



FIG. 212. NAUPLIUS OF EUPHAUSIA. (From Glaus; after Metschnikoff.) The Nauplius is represented shortly before an ecdysis, and in addition to the

proper appendages rudiments of the three following pairs are present.

OL. upper lip ; UL. lower lip ; Md. mandible ; MX', and MX", two pairs of

maxillae ; mf . maxilliped i .

reduced. The cephalo-thoracic shield grows over the front part of the embryo, and becomes characteristically toothed at its edge. There are also

302


468 SCHIZOPODA.


two frontal papillae very similar to those already described in the Phyllopod larvae. Rudiments of the compound eyes make their appearance, and though no new appendages are added, those already present undergo further differentiations. They remain however very simple ; the maxillipeds especially are very short and resemble somewhat Phyllopod appendages.

Up to this stage the tail has remained rudimentary and short, but after a further ecdysis (Claus) it grows greatly in length. At the same time the cephalo-thoracic shield acquires a short spine directed backwards. The larva is now in a condition to which Claus has given the name of Protozoasa (fig. 213 A).

Very shortly afterwards the region immediately following the segments already formed becomes indistinctly segmented, while the tail is still without a trace of segmentation. The region of the thorax proper soon becomes distinctly divided into seven very short segments, while at the same time the now elongated caudal region has become divided into its normal number of segments (fig. 213 B). By this stage the larva has become



FIG. 213. LARVAE OF EUPHAUSIA. (After Claus.) From the side.

A. Protozorea larva. B. Zonea larva.

mx'. and tux", maxillre I and 2 ; mxp^. maxilliped r.

a true Zoaea though differing from the normal Zoaea in the fact that the thoracic region is segmented, and in the absence of a second pair of maxillipeds.

The adult characters are very gradually acquired in a series of successive moults ; the later development of Euphausia resembling in this respect that of the Phyllopods. On the other hand Euphausia differs from that group in the fact that the abdominal (caudal) and thoracic appendages develop as two independent series from before backwards, of which the abdominal series is the earliest to attain maturity.


CRUSTACEA.


469


This is shewn in the following table compiled from Claus' observations.


LENGTH OF LARVA.


APPENDAGES OF THORACIC REGION ; viz. the 2nd and 3rd maxilliped and 5 ambu latory appendages.


APPENDAGES OF ABDOMEN.


3 3^ mm.


2nd maxilliped, rudimentary.


ist abdominal appendage.


3 4 mm.


2nd maxilliped, biramous. 3rd rudimentary, ist and 2nd ambulatory appendages, rudimentary.


2nd and 3rd abdominal appendages. 4th and 5th rudimentary.


4^ 5 mm.


3rd maxilliped, biramous.


4 th, 5th, and 6th fully developed.


55^ mm.


3rd and 4th ambulatory appendages.



6 mm.


5th ambulatory appendage.



All the appendages following the second pair of maxillas are biramous, and the first eight of these bear branched gills as their epipodites. It is remarkable that the epipodite is developed on all the appendages anteriorly in point of time to the outer ramus (exopodite).

Although in Mysis there is no free larval stage, and the development takes place in a maternal incubatory pouch, yet a stage may be detected which clearly corresponds with the Nauplius stage of Euphausia (E. van Beneden, No. 465). At this stage, in which only the three Nauplius appendages are developed, the Mysis embryo is hatched. An ecdysis takes place, but the Nauplius skin is not completely thrown off, and remains as an envelope surrounding the larva during its later development.

Decapoda. Amongst the Decapoda the larva usually leaves the egg in the Zoaea form, but a remarkable exception to this general rule is afforded by the case of one or more species of Penseus. Fritz M tiller was the first to shew that the larva of these forms leaves the egg as a typical Nauplius, and it is probable that in the successive larval stages of these forms the ancestral history of the Decapoda is most fully preserved 1 .

The youngest known larva of Penaeus (fig. 214) has a somewhat oval unsegmented body. There spring from it the three typical pairs of Nauplius appendages. The first is uniramous, the second and third are biramous, and both of them adapted


1 The doubts which have been thrown upon Miiller's observations appear to be quite unfounded.


470 DECAPODA.


for swimming, and the third of them (mandibles) is without a trace of the future blade. The body has no carapace, and bears anteriorly a single median simple eye. Posteriorly it is produced into two bristles.

After the first moult the larva has a rudiment of a forked tail, while a dorsal fold of skin indicates the commencement of



FIG. 214. NAUPLIUS STAGE OF PEN^EUS. (After Fritz Miiller.)

the cephalo-thoracic shield. A large provisional helmet-shaped upper lip like that in Phyllopods has also appeared. Behind the appendages already formed there are stump-like rudiments of the four succeeding pairs (two pairs of maxillae and two pairs of maxillipeds) ; and in a slightly older larva the formation of the mandibular blade has commenced, together with the atrophy of the palp or Nauplius appendage.

Between this and the next observed stage there is possibly a slight lacuna. The next stage (fig. 215) at any rate represents the commencement of the Zoaea series. The cephalo-thoracic shield has greatly grown, and eventually acquires the usual dorsal spine. The posterior region of the body is prolonged into a tail, which is quite as long as the whole of the remainder of the body. The four appendages which were quite functionless at the last stage have now sprouted into full activity. The


CRUSTACEA.


471


region immediately behind them is divided (fig. 215) into six segments (the six thoracic segments) without appendages, while somewhat later the five anterior abdominal segments become indicated, but are equally with the thoracic segments without feet. The mode of appearance of these segments shews that the thoracic and abdominal segments develop in regular succession from before backwards (Claus). Of the palp of the mandibles, as is usual amongst Zosea forms, not a trace remains, though in the youngest Zoaea caught by Fritz Miiller a very small rudiment of the palp was present. The first pair of antennae is unusually long, and the second pair continues to function as a biramous swimming organ ; the outer ramus is multiarticulate. The other appendages are fully jointed, and the two maxillipeds biramous. On the dorsal surface of the body the unpaired eye is still present, but on each side of it traces of the stalked eyes have appeared. Frontal sense organs like those of Phyllopods are also present.

From the Protozoaea form the larva passes into that of a true Zoaea with the usual appendages and spines, characterised however by certain remarkable peculiarities. Of these the most important are (i) the large size of the two pairs of antennae and the retention of its Nauplius function by the second of them ; (2) the fact that the appendages of the six thoracic segments appear as small biramous Schizopod legs, while the abdominal appendages, with the exception of the sixth, are still without



FIG.


215.


PROTOZO^EA STAGE OF PEN/EUS. (After Fritz Miiller.)


472 DECAPODA.


their swimming feet. The early appearance of the appendages of the sixth abdominal segment is probably correlated with their natatory function in connection with the tail. As a point of smaller importance which may be mentioned is the fact that both pairs of maxillae are provided with small respiratory plates (exopodites) for regulating the flow of water under the dorsal shield. From the Zoaea form the larva passes into a Mysis or Schizopod stage (fig. 216), characterised by the thoracic feet and maxillipeds resembling in form and function the biramous feet of Mysis, the outer ramus being at first in many cases much larger than the inner. The gill pouches appear at the base of these feet nearly at the same time as the endopodites become functional. At the same time the antennae become profoundly modified. The anterior antennae shed their long hairs, and from the inner side of the fourth joint there springs a new process,



FIG. 216. PEN^EUS LARVA IN THE MYSIS STAGE. (After Claus.)

which eventually elongates and becomes the inner flagellum. The outer ramus of the posterior antennae is reduced to a scale, while the flagellum is developed from a stump-like rudiment of the inner ramus (Claus). A palp sprouts on the mandible and the median eye disappears.

The abdominal feet do not appear till the commencement of the Mysis stage, and hardly become functional till its close.

From the Mysis stage the larva passes quite simply into the adult form. The outer ramus of the thoracic feet is more or less completely lost. The maxillipeds, or the two anterior pairs at any rate, lose their ambulatory function, cutting plates develop on the inner side of their basal joints, and the two rami persist


CRUSTACEA.


473


as small appendages on their outer side. Gill pouches also sprout from their outer side.

The respiratory plate of the second maxilla attains its full development and that on the first maxilla disappears 1 . The Nauplius, so far as is known, does not occur in any other Decapod form except Penaeus.


The next most primitive larval history known is that which appears in the Sergestidae. The larval history, which has been fully elucidated by Claus, commences with a Protozoaea form (fig. 217), which develops into a remarkable Zoaea first described by Dohrn as Elaphocaris. This develops into a form originally described by Claus as Acanthosoma, and this into a form known as Mastigopus (fig. 218) from which it is easy to pass to the adult.

The remarkable Protozoaea (fig. 217) is characterised by the presence on the dorsal shield of a frontal, dorsal and two lateral spikes, each richly armed with long side spines. The



FIG. 217. LATEST PROTOZO^A STAGE OF SEK GESTES LARVA (ELAPHOCARIS). (After Claus.)


mxp'" '. third pair of maxillipeds.

normal Zoasa appendages are present, and in addition to them a small third pair of maxillipeds. The thoracic region is divided into five short rings, but the abdomen is unsegmented. The tail is forked and provided with long spines. The antennae, like those of Penasus, are long the second pair biramous ; the mandibles unpalped. Both pairs of maxillae are provided with respiratory plates ; the second pair is footlike, and has at its base a glandular mass believed by Claus to be the equivalent of the Entomostracan shell-gland. The maxillipeds have the usual biramous characters. A


1 From Claus' observations (No. 448) it would appear that the respiratory plate is only the exopodite and not, as is usually stated, the coalesced exopodite and epipodite. Huxley in his Comparative Anatomy reserves this point for embryological elucidation.


474


DECAPOD A.



FIG. 218. MASTIGOPUS STAGE OF SERGESTES. (From Claus.) Mf". maxilliped 3.

helmet-shaped upper lip like that of a typical Nauplius is present, and the eyes are situated on very long stalks.

In the true Zoaea stage there appear on the five thoracic

segments pouch-like biramous rudiments of the limbs. The tail becomes segmented; but the segments, with the exception of the sixth, remain without appendages. On the sixth a very long bilobed pouch appears as the commencement of the swimming feet of this segment. The segments of the abdomen are armed with lateral spines.

From the Zoaea stage the larva passes into the form known as Acanthosoma, which represents the Mysis stage of Penaeus. The complex spikes on the dorsal shield of the Zoaea stage are reduced to simple spines, but the spines of the tail still retain their full size. In the appendages the chief changes consist (i) in the reduction of the jointed outer ramus of the second pair of antennae to a stump representing the scale, and the elongation of the inner one to the flagellum ; (2) in the elongation of the five ambulatory thoracic appendages into biramous feet, like the maxillipeds, and in the sprouting forth of rudimentary abdominal feet.


CRUSTACEA.


475


The most obvious external indications of the passage from the Acanthosoma to the Mastigopus stage (fig. 218) are to be found in the elongation of the abdomen, the reduction and flattening of the cephalo-thoracic shield, and the nearly complete obliteration of all the spines but the anterior. The eyes on their elongated stalks are still very characteristic, and the elongation of the flagellum of the second pair of antennae is very striking.

The maxillae and maxillipeds undergo considerable metamorphosis, the abdominal feet attain their adult form, and the three anterior thoracic ambulatory legs lose their outer rami. The most remarkable change of all concerns the two last pairs of thoracic appendages, which, instead of being metamorphosed like the preceding ones, are completely or nearly completely thrown off in the moult which inaugurates the Mastigopus stage, and are subsequently redeveloped. With the reappearance of these appendages, and the changes in the other appendages already indicated, the adult form is practically attained.



FIG. 219. LARVA OF HIPPOLYTE IN ZO/EA STAGE. (From Claus.)

MX', and MX", maxillae i and 2 ; Mf. Mf. Mf". maxillipeds.



FIG. 220.


OLDER LARVA OF HIPPOLYTE AFTER THE THORACIC APPENDAGES HAVE BECOME FORMED. (From Claus.)


476 DECAPODA.


With reference to the development of the majority of the Carabidae, Penaeinae, Palaemoninae, Crangoninae, it may be stated generally that they leave the egg in the Zoaea stage (fig. 219) with anterior appendages up to the third pair of maxillipeds. The thorax is unsegmented and indeed almost unrepresented, but the abdomen is long and divided into distinct segments. Both thoracic and abdominal appendages are absent, and the tail is formed by a simple plate with numerous bristles, not forked, as in the case of the Zoaea of Fritz M tiller's Penaeus and Sergestes. A dorsal spine is frequently found on the second abdominal segment. From the Zoaea form the embryo passes into a Mysis stage (fig. 220), during which the thoracic appendages gradually appear as biramous swimming feet; they



FIG. 221. NEWLY-HATCHED LARVA OF THE AMERICAN LOBSTER. (After Smith.) are all developed before any of the abdominal appendages, except the last. In some cases the development is still further abbreviated. Thus the larvae of Crangon and Palaemonetes (Faxon, No. 476) possess at hatching the rudiments of the two anterior pairs of thoracic feet, and Palaemon of three pairs'.

Amongst the other Macrura the larva generally leaves the egg as a Zoaea similar to that of the prawns. In the case of the

1 Fritz Miiller has recently (Zoologisrher Anzeiger^ No. 52) described a still more abbreviated development of a Pala-mon living in brooks near Blumenau.


CRUSTACEA. 477


Thalassinidae and Paguridae a Mysis stage has disappeared. The most remarkable abbreviations of the typical development are presented on the one hand by Homarus and Astacus, and on the other by the Loricata.

The development of Homarus has been fully worked out by S. J. Smith (No. 491) for the American lobster (Homarus americanus). The larva (fig. 221) leaves the egg in an advanced Mysis stage. The cephalo-thoracic shield is fully developed, and armed with a rostrum in front. The first pair of antennae is unjointed but the second is biramous, the outer ramus forming a large Mysis-like scale. The mandibles, which are palped, the maxillae, and the two anterior maxillipeds differ only in minor details from the same appendages of the adult. The third pair of maxillipeds is Mysis-like and biramous, and the five ambulatory legs closely resemble them, the endopodite of the first being imperfectly chelate. The abdomen is well developed but without appendages. The second, third, fourth and fifth segments are armed with dorsal and lateral spines.

In the next stage swimming feet have appeared on the second, third, fourth and fifth abdominal segments, and the appendages already present have approached their adult form. Still later, when the larva is about half an inch in length, the approach to the adult form is more marked, and the exopodites of the ambulatory legs though present are relatively much reduced in size. The swimmerets of the sixth abdominal segment are formed. In the next stage observed the larva has entirely lost its Schizopod characters, and though still retaining its free swimming habits differs from the adult form only in generic characters.

As has been already stated, no free larval stages occur in the development of Astacus, but the young is hatched in a form in which it differs only in unimportant details from the adult.

The peculiar larval form of the Loricata (Scyllarus, Palinurus) has long been known under the name Phyllosoma (fig. 222 C), but its true nature was first shewn by Couch (No. 474) [Couch did not however recognise the identity of his larva with Phyllosoma ; this was first done by Gerstacker] and shortly afterwards by Gerbe and Coste. These observations were however for a long time not generally accepted, till Dohrn (No. 477) published his valuable memoir giving an account of how he succeeded in actually rearing Phyllosoma from the eggs of Scyllarus and Palinurus, and shewing that some of the most remarkable features of the metamorphosis of the Loricata occur before the larva is hatched.

The embryo of Scyllarus in the egg first of all passes through the usual Nauplius stage, and then after the formation of a cuticle develops an elongated thoracico-abdominal region bent completely over the anterior part of the body. There appear moreover a number of appendages and the rudiments of various organs ; and the embryo passes into a form which may be described as the embryonic Phyllosoma stage. In this stage there are present on the anterior part of the body, in front of the ventral flexure, two


478 DECAPODA.


pairs of antennae, mandibles, two pairs of maxillae, the second commencing to be biramous, and a small stump representing the first pair of maxillipeds. The part of the body bent over consists of a small quadrate caudal plate, and an appendage-bearing region to which are attached anteriorly three pairs of biramous appendages the second and third maxillipeds, and the anterior pair of ambulatory legs and two pairs of undivided appendages the second and third pairs of ambulatory legs. In a slightly later stage the first pair of maxillae becomes biramous, as also does the first pair of maxillipeds in a very rudimentary fashion. The second and third pairs of ambulatory legs become biramous, while the second and third maxilliped nearly completely lose their outer ramus. Very small rudiments of the two hinder ambulatory legs become formed. If the embryo is taken at this stage (vide fig. 222 A, which represents a nearly similar larva of Palinurus) out of the egg, it is seen to consist of (i) an anterior enlargement with a vaulted dorsal shield enclosing the yolk, two stalked eyes, and a median eye ; (2) a thoracic region in which the indications of segmentation are visible with the two



FIG. 222. LARWE OF THE LORICATA. (After Claus.)

A. Embryo of Palinurus shortly before hatching.

B. Young Phyllosoma larva of Scyllarus, without the first maxilliped, the two last thoracic appendages, or the abdominal appendages.

C. Fully-grown Phyllosoma with all the Decapod appendages.

at*, antenna of first pair ; at*, antenna of second pair ; md. mandible ; ntx 1 . first maxilla; mx 1 . second maxilla; mx^mxf. maxillipeds; / 1 / 3 . thoracic appendages.

posterior pairs of maxillipeds (mxfp and wr/ 3 ) and the ambulatory legs (/ l ); (3) an abdominal region distinctly divided into segments and ending in a fork. Before the embryo becomes hatched the first pair of maxillipeds becomes reduced in size and finally vanishes. The second pair of maxillae becomes reduced to simple stumps with a few bristles, the second pair of antennae


CRUSTACEA. 479


also appears to undergo a retrogressive change, while the two last thoracic segments cease to be distinguishable. It thus appears that during embryonic life the second pair of antennae, the second pair of maxillae, and the second and third pair of maxillipeds and the two hinder ambulatory appendages undergo retrogressive changes, while the first pair of maxillipeds is completely obliterated !

The general form of the larva when hatched (fig. 222 B) is not very different from that which it has during the later stages within the egg. The body is divided into three regions: (i) an anterior cephalic; (2) a middle thoracic, and (3) a small posterior abdominal portion ; and all of them are characterised by their extreme dorso-ventral compression, so that the whole animal has the form of a three-lobed disc, the strange appearance of which is much increased by its glass-like transparency.

The cephalic portion is oval and projects slightly behind so as to overlap the thorax. Its upper surface constitutes the dorsal shield, from which there spring anteriorly the two compound eyes on long stalks, between which is a median Nauplius eye. The mouth is situated about the middle of the under surface of the anterior disc. It leads into a stomach from which an anterior and a lateral hepatic diverticulum springs out on each side. The former remains as a simple diverticulum through larval life, but the latter becomes an extremely complicated glandular structure.

At the front border of the disc is placed the unjointed but elongated first pair of antennae (rt/ 1 ). Externally to and behind these there spring the short posterior antennae (at'*}. At the base of which the green gland is already formed. Surrounding the mouth are the mandibles (md) and anterior pair of maxillae (mx 1 ), and some distance behind the second pair of maxillae (mx*), consisting of a cylindrical basal joint and short terminal joint armed with bristles. The first pair of maxillipeds is absent.

The thoracic region is formed of an oval segmented disc attached to the under surface of the cephalic disc. From its front segment arises the second pair of maxillipeds (inxp l } as single five-jointed appendages, and from the next segment springs the five-jointed elongated but uniramous third pair of maxillipeds (mxfl 3 }, and behind this there arise three pairs of six-jointed ambulatory appendages (p\ / 2 , p 3 , of which only the basal joint is represented in the figure) with an exopodite springing from their second joint. The two posterior thoracic rings and their appendages cannot be made out.

The abdomen is reduced to a short imperfectly segmented stump, ending in a fork, between the prongs of which the anus opens. Even the youngest larval Phyllosoma, such as has just been described, cannot be compared with a Zoaea, but belongs rather, in the possession of biramous thoracic feet, to a Mysis stage. In the forked tail and Nauplius eye there appear however to be certain very primitive characters carried on to this stage.

The passage of this young larva to the fully formed Phyllosoma (fig. 222 C) is very simple. It consists essentially in the fresh development of the first pair of maxillipeds and the two last ambulatory appendages, the growth and segmentation of the abdomen, and the sprouting on it of biramous


480 DECAPODA.


swimming feet. In the course of these changes the larva becomes a true Decapod in the arrangement and number of its appendages ; and indeed it was united with this group before its larval character was made out. In addition to the appearance of new appendages certain changes take place in those already present. The two posterior maxillipeds, in the Palinurus Phyllosoma at any rate, acquire again an exopodite, and together with the biramous ambulatory feet develop epipodites in the form of gill pouches.

The mode of passage of the Phyllosoma to the adult is not known, but it can easily be seen from the oldest Phyllosoma forms that the dorsal cephalic plate grows over the thorax, and gives rise to the cephalo-thoracic shield of the adult.

There are slight structural differences, especially in the antennae, between the Phyllosoma of Scyllarus and that of Palinurus, but the chief difference in development is that the first pair of maxillipeds of the Palinurus embryo, though reduced in the embryonic state, does not completely vanish, at any rate till after the free larval state has commenced ; and it is doubtful if it does so even then. The freshly hatched Palinurus Phyllosoma is very considerably more developed than that of Scyllarus.

Brachyura. All the Brachyura, with the exception of one or more species of land crabs 1 , leave the egg in the Zoaia condition, and though there are slight variations of structure, yet on the



FIG. 223. THE APPENDAGES OF A CRAB ZOJEA.

At. I. first antenna ; At. //. second antenna ; md. mandible (without a palp) ; mx. i. first maxilla ; mx. i. second maxilla ; w.r. 3. third maxilla ; mxp. i. first maxilliped ; mxp. i. second maxilliped.

ex. exopodite ; ett. cndopodite.

whole the Crab Zoaea is a very well marked form. Immediately after leaving the egg (fig. 210) it has a somewhat oval shape

1 It has been clearly demonstrated that the majority of land-crabs leave the egg in the 7.oxa. form.


CRUSTACEA. 481


with a long distinctly-segmented abdomen bent underneath the thorax. The cephalo-thoracic shield covers over the front part of the body, and is prolonged into a long frontal spine pointing forwards, and springing from the region between the two eyes ; a long dorsal spine pointing backwards ; and two lateral spines.

To the under surface of the body are attached the anterior appendages up to the second maxilliped, while the six following pairs of thoracic appendages are either absent or represented only in a very rudimentary form. The abdomen is without appendages.

The anterior antennae are single and unjointed, but provided at their extremity with a few olfactory hairs (only two in Carcinus Mcenas) and one or two bristles. The rudiment of the secondary flageltum appears in very young Zoaeae on the inner side of the antennules (fig. 223 At. /.). The posterior antennae are without the flagellum, but are provided with a scale representing the exopodite (fig. 223 At. II. ex] and usually a spinous



FIG. 224. CRAB ZO^EA AFTER TH.. THIRD PAIR OF MAXILLIPEDS AND THE

THORACIC AND ABDOMINAL APPENDAGES HAVE BECOME DEVELOPED.

at 1 , antenna of first pair ; at z . antenna of second pair ; mx l . first maxilla ; mop. second maxilla ; mxp 1 . first maxilliped ; mxjP. second maxilliped ; mxf. third maxilliped ; oc. eye ; ht. heart.

process. The flagellum is very early developed and is represented in fig. 223, At. II. en. The mandibles (md) are large but without a palp. The anterior maxillae (mx i) have a short twojointed endopodite (palp) with a few hairs, and a basal portion B. II. 31


-


482 DECAPODA.


with two blades, of which the distal is the largest, both armed with stiff bristles. The posterior maxillae have a small respiratory plate (exopodite), an endopodite (palp) shaped like a double blade, and two basal joints each continued into a double blade. The two maxillipeds (inxp i and mxp 2) have the form and function of biramous swimming feet. The exopodite of both is two-jointed and bears long bristles at its extremity ; the endopodite of the anterior is five-jointed and long, that of the second is three-jointed and comparatively short.

In the six-jointed tail the second segment has usually two dorsally directed spines, and the three succeeding segments each of them two posteriorly directed. The telson or swimming plate is not at first separated from the sixth segment ; on each side it is prolonged into two well-marked prongs ; and to each prong three bristles are usually attached (fig. 224). The heart (fig. 224 ht) lies under the dorsal spine and is prolonged into an anterior, posterior, and dorsal aorta. It has only two pairs of venous ostia.

During the Zoaea stage the larva rapidly grows in size, and undergoes considerable changes in its appendages which reach the full Decapod number (fig. 224). On both pairs of antennae a flagellum becomes developed and grows considerably in length. Before the close of the Zoaea condition a small and unjointed palp appears on the mandible. Behind the second maxilliped the third maxilliped (inxp*} early appears as a small biramous appendage, and the five ambulatory feet become distinctly formed as uniramous appendages the exopodites not being present. The third pair of maxillipeds and three following ambulatory appendages develop gill pouches. The abdominal feet are formed on the second to the sixth segments of the tail as simple pouches.

The oldest Zoaea is transmuted at its moult into a form known as Megalopa, which is really almost identical with an anomurous Decapod. No Schizopod stage is intercalated, which shews that the development is in many respects greatly abbreviated. The essential characters of the Megalopa are to be found in (i) the reduction of the two anterior maxillipeds, which cease to function as swimming feet, and together with the appendages in front of them assume the adult form ; (2) the full


CRUSTACEA. 483


functional development of the five ambulatory appendages ; (3) the reduction of the forked telson to an oval swimming plate, and the growth in size of the abdominal feet, which become large swimming plates and are at the same time provided with short endopodites which serve to lock the feet of the two sides.

With these essential characters the form of the Megalopa differs considerably in different cases. In some instances (e.g. Carcinus mcenas) the Zoasa spines of the youngest Megalopa are so large that the larva appears almost more like a Zoasa than a Megalopa (Spence Bate, No. 470). In other cases, e.g. that represented on fig. 225, the Zoasa spines are still present but much reduced; and the cephalo-thoracic shield has very much the adult form. In other cases again (e.g. Portunus) the Zoasa spines are completely thrown off at the youngest Megalopa stage.

There is a gradual passage from the youngest Megalopa to the adult form by a series of moults.

Some of the brachyurous Zoasa forms exhibit considerable divergences from the described type, more espcially in the armature of the shield. In some forms the spines are altogether absent, e.g. Maja (Couch, No. 474) and Eurynome. In other forms the frontal spine may be much reduced or absent (Inachus and Achasus). The dorsal spine may also be absent, and in one form described by Dohrn (No. 478) there is a long frontal spine and two pairs of lateral spines, but no dorsal ^ MEGALOPA STAGE OF CRAB LARVA.

spine. Both dorsal and

frontal spines may attain enormous dimensions and be swollen at their extremities (Dohrn). A form has been described by Claus as Pterocaris in which the cephalo-thoracic shield is laterally expanded into two wing-like processes.

The Zoasa of Porcellana presents on the whole the most remarkable peculiarities and, as might be anticipated from the systematic position of the adult, is in some respects intermediate between the macrurous Zoasa and that of the Brachyura. It is characterized by the oval form of the body, and by

31-2



484 STOMATOPODA.


the presence of one enormously long frontal spine and two posterior spines. The usual dorsal spine is absent. The tail plate is rounded and has the character of the tail of a macrurous Zoaea, but in the young Zoasa the third pair of maxillipeds is absent and the appendages generally have a brachyurous character. A Megalopa stage is hardly represented, since the adult may almost be regarded as a permanent Megalopa.

Stomatopoda. The history of the larval forms of the Stomatopoda (Squilla etc.) has not unfortunately been thoroughly worked out, but what is known from the researches of Fritz Miiller (No. 495) and Claus (No. 494) is of very great importance. There are it appears two types, both of which used to be described as adult forms under the respective names Erichthus and Alima.

The youngest known Erichthus form is about two millimetres in length, and has the characters of a modified Zoaea (fig. 226). The body is divided into three regions, an anterior unsegmented region to which are attached two pairs of antennas, mandibles, and maxillae (two pairs). This portion has a dorsal shield covering the next or middle region, which consists of five segments each with a pair of biramous appendages. These appendages represent the five maxillipeds of the adult 1 . The portion of the body behind this is without appendages. It consists of three short anterior segments, the three posterior thoracic segments of the adult, and a long unsegmented tail. The three footless thoracic segments are covered by the dorsal shield. Both pairs of antennae are uniramous and comparatively short. The mandibles, like those of Phyllopods, are without palps, and the two following pairs of maxillae are small. The five maxillipeds have the characters of normal biramous Zoaea feet. From the front of the head spring a pair of compound eyes with short stalks, which grow longer in the succeeding stages ; between them is a median eye. The dorsal shield is attached just behind this eye, and is provided, as in the typical Zoaea, with a frontal spike while its hinder border is produced into two lateral spikes and one median. In a larva of about three millimetres a pair of biramous appendages arises behind the three footless thoracic segments. It is the anterior pair of abdominal feet (fig. 226). The inner ramus of the second pair of maxillipeds soon grows greatly in length, indicating its subsequent larger size and prehensile form (fig. 227 g). When the larva after one or

two moults attains a length FlG - 6 - SECOND STAGE OF ERICHTHUS of six millimetres Cfitr 227 1 LARVA OFSQUII.LA WITH FIVE MAXILLIPEDS AND

(tig. 227) THE FIRST PAIR OF ABDOMINAL APPENDAGES.

the abdomen has six segments (From Claus.)

1 These five maxillipeds correspond with the three maxillipeds and two anterior ambulatory appendages of the Decapoda.



CRUSTACEA.


485


(the sixth hardly differentiated), each with a pair of appendages (the two hindermost still rudimentary) which have become gradually developed from before backwards. The three hindermost thoracic segments are still without appendages.

Some changes of importance have occurred in the other parts. Both antennas have acquired a second flagellum, but the mandible is still without



FIG. 227. ADVANCED ERICHTHUS LARVA OF SQUILLA WITH FIVE PAIRS OF

ABDOMINAL APPENDAGES. (From Claus.)

f. first maxilliped ; g. second maxilliped.

a palp. The first and second pair of maxillipeds have both undergone important modifications. Their outer ramus (exopodite) has been thrown off, and a gill-plate (epipodite) has appeared as an outgrowth from their basal joint. Each of them is composed of six joints. The three following biramous appendages have retained their earlier characters but have become much reduced in size. In the subsequent moults the most remarkable new features concern the three posterior maxillipeds, which undergo atrophy, and are either completely lost or reduced to mere unjointed sacks (fig. 228). In



FIG. 228. ADVANCED ERICHTHUS LARVA OF SQUILLA WHEN THE THREE POSTERIOR MAXILLIPEDS HAVE BECOME REDUCED TO MINUTE POUCHES.

(From Claus.)

the stage where the complete Erichthus type has been reached, these three appendages have again sprouted forth in their permanent form and each of them is provided with a gill-sack on its coxal joint. Behind them the three ambulatory appendages of the thorax have also appeared, first as simple buds, which subsequently however become biramous. On their development the full number of adult appendages is acquired.

The most noteworthy points in the developmental history detailed above are the following :

(i) The thoracic and abdominal segments (apart from their appendages) develop successively from before backwards.


486 STOMATOPODA.


(2) The three last maxillipeds develop before the abdominal feet, as biramous appendages, but subsequently completely atrophy, and then sprout out again in their permanent form.

(3) The abdominal feet develop in succession from before backwards, and the whole series of them is fully formed before a trace of the appendages of the three hindermost thoracic segments has appeared. It may be mentioned as a point of some importance that the Zoaea of Squilla has an elongated many-chambered heart, and not the short compact heart usually found in the Zoaea.

The younger stages of the Alima larva are not known 1 , but the earliest stage observed is remarkable for presenting no trace of the three posterior pairs of maxillipeds, or of the three following pairs of thoracic appendages. The segments belonging to these appendages are however well developed. The tail has its full complement of segments with the normal number of well developed swimming feet. The larva represents in fact the stage of the Erichthus larva when the three posterior pairs of maxillipeds have undergone atrophy ; but it is probable that these appendages never become developed in this form of larva.

Apart from the above peculiarities the Alima form of larva closely resembles the Erichthus form.

Nebaliadae. The development of Nebalia is abbreviated, but from MetschnikofFs figures 2 may be seen to resemble closely that of Mysis. The abdomen has comparatively little yolk, and is bent over the ventral surface of the thorax. There is in the egg a Nauplius stage with three appendages, and subsequently a stage with the Zoaea appendages.

The larva when it leaves the egg has the majority of its appendages formed, but is still enveloped in a larval skin, and like Mysis bends its abdomen towards the dorsal side. When the larva is finally hatched it does not differ greatly from the adult.

Cum ace ae. The development of the Cumaceae takes place for the most part within the egg, and has been shewn by Dohrn (No. 496) to resemble in many points that of the Isopods. A dorsal organ is present, and a fold is formed immediately behind this which gives to the embryo a dorsal flexure. Both of these features are eminently characteristic of the Isopoda.

The formation of the two pairs of antennie, mandibles, and two pairs of maxillae and the following seven pairs of appendages takes place very early. The pair of appendages behind the second maxilku assumes an ambulatory form, and exhibits a Schizopod character very early, differing in both these respects from the homologous appendages in the Isopoda. The cephalo-thoracic shield commences to be formed when the appendages are still quite rudimentary as a pair of folds in the maxillary region. The

1 The observations of Brooks (No. 493) render it probable that the Alima larva leaves the egg in a form not very dissimilar to the youngest known larva. 3 His paper is unfortunately in Russian.


CRUSTACEA. 487


eyes are formed slightly later on each side of the head, and only coalesce at a subsequent period to form the peculiar median sessile eye of the adult.

The two pairs of appendages behind the second maxillae become converted into maxillipeds, and the exopodite of the first of them becomes the main ramus, while in the externally similar second maxilliped the exopodite atrophies and the endopodite alone remains.

The larva is hatched without the last pair of thoracic limbs or the abdominal appendages (which are never developed in the female), but in other respects closely resembles the adult. Before hatching the dorsal flexure is exchanged for a ventral one, and the larva acquires a character more like that of a Decapod.

COPEPODA.

Natantia. The free Copepoda are undoubtedly amongst the lowest forms of those Crustacea which are free or do not lead a parasitic existence. Although some features of their anatomy, such for instance as the frequent absence of a heart, may be put down to a retrogressive development, yet, from their retention of the median frontal eye of the Nauplius as the sole organ of vision 1 , their simple biramous swimming legs, and other characters, they may claim to be very primitive forms, which have diverged to no great extent from the main line of Crustacean development. They supply a long series of transitional steps from the Nauplius stage to the adult condition.

While still within the egg-shell the embryo is divided by two transverse constrictions into three segments, on which the three Nauplius appendages are developed, viz. the two pairs of antennae and the mandibles. When the embryo is hatched the indication of a division into segments has vanished, but the larva is in the fullest sense a typical Nauplius 2 . There are slight variations in the shape of the Nauplius in different genera, but its general form and character are very constant. It has (fig. 229 A) an oval unsegmented body with three pairs of appendages springing from the ventral surface. The anterior of these (at i) is uniramous, and usually formed of three joints which bear bristles on their under surface. The two posterior

1 The Pontellidse form an exception to this statement, in that they are provided with paired lateral eyes in addition to the median one.

2 The term Nauplius was applied to the larva of Cyclops and allied organisms by O. F. Muller under the impression that they were adult forms.


488


COPEPODA.


pairs of appendages are both biramous. The second pair of antennae (at 2) is the largest. Its basal portion (protopodite) bears on its inner side a powerful hook-like bristle. The outer ramus is the longest and many-jointed ; the inner ramus has only two joints. The mandibles (md), though smaller than the second pair of antennae, have a nearly identical structure. No blade-like projection is as yet developed on their protopodite. Between the points of insertion of the first pair of antennae is the median eye (oc), which originates by the coalescence of two distinct parts. The mouth is ventral, and placed in the middle line between the second pair of antennae and the mandibles : it



FIG. 229. SUCCESSIVE STAGES IN THE DEVELOPMENT OF CYCLOPS TENUICORMS.

(Copied from Bronn ; after Claus.)

A. B. and C. Nauplius stages. D. Youngest Copepod stage. In this figure maxillae and the two rami of the maxilliped are seen immediately behind the mandible md.

oc. eye ; at 1 , first pair of antennae ; a/ 8 , second pair of antennre ; md. mandible ; /*. first pair of feet ; / 2 . second pair of feet ; f. third pair of feet ; //. excretory concretions in the intestine.

is provided with an unpaired upper lip. There are two bristles at the hind end of the embryo between which the anus is placed, and in some cases there is at this part a slight indication of the future caudal fork.

The larva undergoes a number of successive ecdyses, at each of which the body becomes more elongated, and certain other


CRUSTACEA. 489


changes take place. First of all a pair of appendages arises behind the mandibles, which form the maxillae (fig. 229 B) ; at the same time the basal joint of the maxillae develops a cuttingblade. Three successive pairs of appendages (fig. 229 C) next become formed the so-called maxillipeds (the homologues of the second pair of maxillae), and the two first thoracic limbs. Each of these though very rudimentary is nevertheless bifid. The body becomes greatly elongated, and the caudal fork more developed.

Up to this stage of development the Nauplius appendages have retained their primitive character almost unaltered ; but after a few more ecdyses a sudden change takes place ; a cephalothoracic shield becomes fully developed, and the larva comes to resemble in character an adult Copepod, from which it mainly differs in the smaller number of segments and appendages. In the earliest 'Cyclops' stage the same number of appendages are present as in the last Nauplius stage. There (fig. 229 D) is a well developed cephalo-thorax, and four free segments behind it. To the cephalo-thoracic region the antennae, mandibles, maxillae, the now double pair of maxillipeds (derived from the original single pair of appendages), and first pair of thoracic appendages (p l ) are attached. The second pair of thoracic appendages (/ 2 ) is fixed to the first free segment, and the rudiment of a third pair (/ 3 ) projects from the second free segment. The first pair of antennae has grown longer by the addition of new joints, and continues to increase in length in the following ecdyses till it attains its full adult development, and then forms the chief organ of locomotion. The second pair of antennae is much reduced and has lost one of its rami. The two rami of the mandibles are reduced to a simple palp, while the blade has assumed its full importance. The maxillae and following appendages have greatly increased in size. They are all biramous, though the two rami are not as yet jointed. The adult state is gradually attained after a number of successive ecdyses, at which new segments and appendages are added, while new joints are formed for those already present.

Parasita. The earliest developmental stages of the parasitic types of Copepoda closely resemble those of the free forms, but, as might be expected from the peculiarly modified forms of the adult, they present a


490


COPEPODA.


large number of secondary characters. So far as is known a more or less modified Nauplius larva is usually preserved.

The development of Achtheres percarum, one of the Lernaeopoda parasitic in the mouth, etc. of the common Perch, may be selected to illustrate the mode of development of these forms. The larva leaves the egg as a much simplified Nauplius (fig. 230 A). It has an oval body with only the two anterior pairs of Nauplius appendages ; both of them in the rudimentary condition of unjointed rods. The usual median eye is present, and there is also found a peculiar sternal papilla, on which opens a spiral canal filled with a glutinous material, which is probably derived from a gland which disappears on the completion of the duct. The probable function of this



FIG. 330. SUCCESSIVE STAGES IN THE DEVELOPMENT OF ACHTHERES PERCARUM. (Copied from Bronn ; after Claus. )

A. Modified Nauplius stage. B. Cyclops stage. C. Late stage of male embryo. D. Sexually mature female. E. Sexually mature male.

at 1 , first pair of antennae; at 3 , second pair of antennae; tnd. mandible; tnx. maxillae ; ptn 1 . outer pair of maxillipeds ; ftn^. inner pair of maxillipeds ; J> 1 . first pair of legs ; /*. second pair of legs ; z. frontal organ ; i. intestine ; o. larval eye ; b. glandular body ; t. organ of touch ; ov. ovary ; /. rod projecting from coalesced maxillipeds ; g. cement gland ; rs. receptaculurn seminis ; n. nervous system ; te. testis ; v. vas deferens.

organ is to assist at a later period in the attachment of the parasite to its host. Underneath the Nauplius skin a number of appendages are visible, which become functional after the first ecdysis. This takes place within a few hours after the hatching of the Nauplius, and the larva then passes from


CRUSTACEA. 491


this rudimentary Nauplius stage into a stage corresponding with the Cyclops stage of the free forms (fig. 230 B). In the Cyclops stage the larva has an elongated body with a large cephalo-thoracic shield, and four free posterior segments, the last of which bears a forked tail.

There are now present eight pairs of appendages, viz. antennae (two pairs), mandibles, maxillae, maxillipeds, and three pairs of swimming feet. The Nauplius appendages are greatly modified. The first pair of antennae is three-jointed, and the second biramous. The outer ramus is the longest, and bears a claw-like bristle at its extremity. This pair of appendages is used by the larva for fixing itself. The mandibles are small and connected with the proboscidiform mouth ; and the single pair of maxillae is small and palped. The maxillipeds (pm* and flm 2 ) are believed by Claus to be primitively a single biramous appendage, but early appear as two distinct structures 1 , the outer and larger of which becomes the main organ by which the larva is fixed. Both are at this stage simple two-jointed appendages. The two anterior pairs of swimming feet have the typical structure, and consist of a protopodite bearing an unjointed exopodite and endopodite. The first pair is attached to the cephalo-thorax and the second (p*} to the first free thoracic segment. The third pair is very small and attached to the second free segment. The mouth is situated at the end of a kind of proboscis formed by prolongations of the upper and lower lips. The alimentary tract is fairly simple, and the anus opens between the caudal forks.

Between this and the next known stage it is quite possible that one or more may intervene. However this may be the larva in the next stage observed (fig. 230 C) has already become parasitic in the mouth of the Perch, and has acquired an elongated vermiform aspect. The body is divided into two sections, an anterior unsegmented, and a posterior formed of five segments, of which the foremost is the first thoracic segment which in the earlier stage was fused with the cephalo-thorax. The tail bears a rudimentary fork between the prongs of which the anus opens. The swimming feet have disappeared, so also has the eye and the spiral duct of the embryonic frontal organ. The outer of the two divisions of the maxilliped have undergone the most important modification, in that they have become united at their ends, where they form an organ from which an elongated rod (_/) projects, and attaches the larva to the mouth or gills of its host. The antennae and jaws have nearly acquired their adult form. The nervous system consists of supra- and infra-cesophageal ganglia and two lateral trunks given off from the latter. At this stage the males and females can already be distinguished, not only by certain differences in the rudimentary generative organs, but also by the fact that the outer branch of the maxillipeds is much longer in the female than in the male, and projects beyond the head.

In the next ecdysis the adult condition is reached. The outer maxilli 1 Van Beneden (No. 506) in the genera investigated by him finds that the two maxillipeds are really distinct pairs of appendages.


492 CIRRIPEDIA.


peds of the male (fig. 230 ,/>#*) separate again ; while in the female (fig. 230 D) they remain fused and develop a sucker. The male is only about one-fifth the length of the female. In both sexes the abdomen is much reduced.

In the genera Anchorella, Lernaeopoda, Brachiella and Hessia, Ed. van BenecUn (No. 506) has shewn that the embryo, although it passes through a crypto-Nauplius stage in the egg, is when hatched already in the Cyclops stage.

Branchiura. The peculiar parasite Argulus, the affinities of which with the Copepoda have been demonstrated by Claus (No. 511), is hatched in a Cyclops stage, and has no Nauplius stage. At the time of hatching it closely resembles the adult in general form. Its appendages are however very nearly those of a typical larval Copepod. The body is composed of a cephalo-thorax and free region behind this. The cephalo-thorax bears on its under surface antennae (two pairs), mandibles, maxillipeds, and the first pair of thoracic feet.

The first pair of antennae is three-jointed, but the basal joint bears a hook. The second pair is biramous, the inner ramus terminating in a hook. The mandible is palped, but the palp is completely separated from the cutting blade 1 . The maxilla would, according to Claus, appear to be absent.

The two typical divisions of the Copepod maxillipeds are present, viz. an outer and anterior larger division, and an inner and posterior smaller one. The first pair of thoracic feet, as is usual amongst Copepoda, is attached to the cephalo-thorax. It has not the typical biramous Copepod character. There are four free segments behind the cephalo-thorax, the last of which ends in a fork. Three of them bear appendages, which are rudimentary in this early larval stage. On the dorsal surface are present paired eyes as well as an unpaired median eye.

Between the larval condition and that of the adult a number of ecdyses intervene.

CIRRIPEDIA.

The larvae of all the Cirripedia, with one or two exceptions, leave the egg in the Nauplius condition. The Nauplii differ somewhat in the separate groups, and the post-nauplial stages vary not inconsiderably.

It will be most convenient to treat successively the larval

1 It seems not impossible that the appendage regarded by Claus as the mandibular palp may really represent the maxilla, which would otherwise seem to be absent. This mode of interpretation would bring the appendages of Argulus into a much closer agreement with those of the parasitic Copepoda. It does not seem incompatible with the existence of the stylet-like maxillse detected by Claus in the adult.


CRUSTACEA. 493


history of the four sub-orders, viz. Thoracica, Abdominalia, Apoda, and Rhizocephala.

Thoracica. The just hatched larvae at once leave the egg lamellae of their parent. They pass out through an opening in the mantle near the mouth, and during this passage the shell of the parent is opened and the movements of the cirriform feet cease.

The larval stages commence with a Nauplius 1 which, though regarded by Claus as closely resembling the Copepod Nauplius (figs. 231 and 232 A), certainly has very marked pecularities of its own, and in some respects approaches the Phyllopod Nauplius. It is in the youngest stage somewhat triangular in form, and covered on the dorsal side by a very delicate and hardly perceptible dorsal shield, which is prolonged laterally into two very peculiar conical horns (fig. 231 Ik), which are the most characteristic structures of the Cirriped Nauplius. They are connected with a glandular mass, the secretion from which passes out at their apex. Anteriorly the dorsal shield has the same extension as the body, but posteriorly it projects slightly.

An unpaired eye is situated on the ventral surface of the head, and immediately behind it there springs a more or less considerable upper lip (Ib), which resembles the Phyllopod labrum rather than that of the Copepoda. Both mouth and anus are present, and the hind end of the body is slightly forked in some forms, but ends in others, e.g. Lepas fascicularis, in an elongated spine. The anterior of the three pairs of Nauplius appendages (At*) is uniramous, and the two posterior (Af and md) are biramous. From the protopodites of both the latter spring strong hooks like those of the Copepod and Phyllopod Nauplii. In some Nauplii, e.g. that of Balanus, the appendages are at first not jointed, but in other Nauplii, e.g. that of Lepas fascicularis, the jointing is well marked. In Lepas fascicularis the earliest free Nauplius is enveloped in a larval skin, which is thrown off after a few hours. The Nauplii of all the Thoracica undergo a considerable number of moults before their appendages increase in number or segmentation of the body appears. During these moults they grow larger, and the posterior part of the

1 Alepas squalicola is stated by Koren and Danielssen to form an exception to this rule, and to leave the egg with six pairs of appendages.


494


CIRRIPEDIA.


body the future thoracic and abdominal region grows relatively in length. There also appear close to the sides of the unpaired eye two conical bodies, which correspond with the frontal sense organs of the Phyllopods. During their growth the different larvae undergo changes varying greatly in degree.

In Balanus the changes consist for the most part in the full segmentation of the appendages and the growth and distinctness



FIG. 231. NAUPLIUS LARVA OF LEPAS FASCICULARIS VIEWED FROM THE SIDE. oc. eye ; At. i. antenna of first pair ; At. 2. antenna of second pair ; md. mandible ; Ib. labrum ; an. anus; me. mesenteron; d.sp. dorsal spine; c.sp. caudal spine; Vp. ventral spine ; Ih. lateral horns.

of the dorsal shield, which forms a somewhat blunt triangular plate, broadest in front, with the anterior horns very long, and two short posterior spines. The tail also becomes produced into a long spine.

In Lepas fascicularis the changes in appearance of the Nauplius, owing to a great spinous development on its shield, are very considerable ; and, together with its enormous size, render it a very remarkable form. Dohrn (No. 520), who was the first to describe it, named it Archizoaea gigas.


CRUSTACEA. 495


The dorsal shield of the Nauplius of Lepas fascicularis (fig. 231) becomes somewhat hexagonal, and there springs from the middle of the dorsal surface an enormously long spine (d,sp], like the dorsal spine of a Zoa^a. The hind end of the shield is also produced into a long caudal spine (c.sfi] between which and the dorsal spine are some feather-like processes. From its edge there spring in addition to the primitive frontal horns three main pairs of horns, one pair anterior, one lateral, and one posterior, and smaller ones in addition. All these processes (with the exception of the dorsal and posterior spines) are hollow and open at their extremities, and like the primitive frontal horns contain the ducts of glands situated under the shield. On the under surface of the larva is situated the unpaired eye (pc] on each side of which spring the two-jointed frontal sense organs. Immediately behind these is the enormous upper lip (lb] which covers the mouth 1 . At the sides of the lip lie the three pairs of Nauplius appendages, which are very characteristic but present no special peculiarities. Posteriorly the body is produced into a long ventral spine-like process ( Vfi) homologous with that of other more normal Nauplii. At the base of this process large moveable paired spines appear at successive moults, six pairs being eventually formed. These spines give to the region in which they are situated a segmented appearance, and perhaps similar structures have given rise to the appearance of segmentation in Spence Bate's figures. The anus is situated on the dorsal side of this ventral process, and between it and the caudal spine of the shield above. The fact that the anus occupies this position appears to indicate that the ventral process is homologous with the caudal fork of the Copepoda, on the dorsal side of which the anus so often opens 2 .

From the Nauplius condition the larvae pass at a single moult into an entirely different condition known as the Cypris stage. In preparation for this condition there appear, during the last Nauplius moults, the rudiments of several fresh organs, which are more or less developed in different types. In the first place a compound eye is formed on each side of the median eye. Secondly there appears behind the mandibles a fourth pair of appendages the first pair of maxillae and internal to these a pair of small prominences, which are perhaps

1 Willemoes Suhm (No. 530) states that the mouth is situated at the free end of the upper lip, and that the oesophagus passes through it. From an examination of some specimens of this Nauplius, for which I am indebted to Moseley, I am inclined to think that this is a mistake, and that a groove on the surface of the upper lip has been taken by Suhm for the oesophagus.

2 The enormous spinous development of the larva of Lepas fascicularis is probably to be explained as a secondary protective adaptation, and has no genetic connection with the somewhat similar spinous armature of the Zosea.


496" CIRRIPEDIA.


equivalent to the second pair of maxillae, and give rise to the third pair of jaws in the adult (sometimes spoken of as the lower lip).

Behind these appendages there are moreover formed the rudiments of six pairs of feet. Under the cuticle of the first pair of antennae there may be seen just before the final moult the fourjointed antennae of the Cypris stage with the rudiment of a disc on the second joint by which the larvae eventually become attached.

By the free Cypris stage, into which the larva next passes, a very complete metamorphosis has been effected. The median and paired eyes are present as before, but the dorsal shield has become a bivalve shell, the two valves of which are united along their dorsal, anterior, and posterior margins. The two valves are further kept in place by an adductor muscle situated close below the mouth. Remains of the lateral horns still persist. The anterior antennae have undergone the metamorphosis already indicated. They are four-jointed, the two basal joints being long, and the second provided with a suctorial disc, in the centre of which is the opening of the duct of the so-called antennary or cement gland, which is a granular mass lying on the ventral side of the anterior region of the body. The gland arises (Willemoes Suhm) during the Nauplius stage in the large upper lip. The two distal joints of the antennae are short, and the last of them is provided with olfactory hairs. The great upper lip and second pair of antennae and mandibles have disappeared, but a small papilla, forming the commencement of the adult mandibles, is perhaps developed in the base of the Nauplius mandibles. The first pair of maxillae have become small papillae and the second pair probably remain. The six posterior pairs of appendages have grown out as functional biramous swimming feet, which can project beyond the shell and are used in the locomotion of the larva. They are composed of two basal joints, and two rami with swimming hairs, each two-jointed. These feet resemble Copepod feet, and form the main ground for the views of Claus and others that the Copepoda and Cirripedia are closely related. They are regarded by Claus as representing the five pairs of natatory feet of Copepoda, and the generative appendages of the segment behind these. Between


CRUSTACEA.


497


the natatory feet are delicate chitinous lamellae, in the spaces between which the cirriform feet of the adult become developed. The ventral spinous process of the Nauplius stage is much reduced, though usually three-jointed. It becomes completely aborted after the larva is fixed.

In addition to the antennary gland there is present, near the dorsal side of the body above the natatory feet, a peculiar paired glandular mass, the origin of which has not been clearly made out, but which is perhaps equivalent to the entomostracan shell gland. It probably supplies the material for the shell in succeeding stages 1 .

The free Cypris stage is not of long duration ; and during it the larva does not take food. It is succeeded by a stage known as the pupa stage (fig. 232 B), in which the larva becomes fixed, while underneath the larval skin the adult structures are developed. This stage fully deserves its name, since it is a quiescent stage during which no nutriment is taken. The attachment takes place by the sucker of the antennae, and the cement gland (/) supplies the cementing material for effecting it. A retrogressive metamorphosis of a large number of the organs sets in, while at the same time the formation of new adult structures is proceeded with. The eyes become gradually lost, but the Nauplius eye is retained,though in a rudimentary state, and the terminal joints of the antennae with their olfactory hairs are thrown off. The bivalve shell is moulted about the same time as the eyes, the skin below it remaining as the mantle. The caudal process becomes aborted. Underneath the natatory



FIG. 232. LARVAL FORMS OF THE THORACICA. (From Huxley.)

A. Nauplius of Balanus balanoides. (After Sp. Bate.) B. Pupa stage of Lepas australis. (After Darwin.)

n. antennary apodemes ; /. cement gland with duct to antenna.


1 There is considerable confusion about the shell gland and antennary gland. In my account Willemoes Suhm has been followed. Claus however regards what I have called the antennary gland as the shell gland, and states that it does not open into the antennae till a later period. He does not clearly describe its opening, nor the organ which I have called the shell gland.

B. II. 32


498 CIRRIPEDIA.


feet, and between the above-mentioned chitinous lamellae, the cirriform feet are formed ; and on their completion the natatory feet become thrown off and replaced by the permanent feet. In the Lepadidae, in which the metamorphosis of the pupa stages has been most fully studied, the anterior part of the body with the antennae gradually grows out into an elongated stalk, into which pass the ovaries, which are formed during the Cypris stage. At the base of the stalk is the protuberant mouth, the appendages of which soon attain a higher development than in the Cypris stage. At the front part of it a large upper lip becomes formed. Above the mantle and between it and the shell there are formed in the Lepadidae the provisional valves of the shell. These valves are chitinous, and have a fenestrated structure, owing to the chitin being deposited round the margin of the separate epidermis (hypodermis) cells. These valves in the Lepadidae " prefigure in shape, size, and direction of growth, the shelly valves to be formed under and around them" (Darwin, No. 519, p. 129).

Whatever may be the number of valves in the adult the provisional valves never exceed five, viz. the two scuta, the two terga and the carina. They are relatively far smaller than the permanent valves and are therefore separated by considerable membranous intervals. They are often preserved for a long time on the permanent calcareous valves. In the Balanidce the embryonic valves are membranous and do not overlap, but do not present the peculiar fenestrated structure of the primordial valves of the Lepadidae.

In connection with the moult of the pupa skin, and the conversion of the pupa into the adult form, a remarkable change in the position takes place. The pupa lies with the ventral side parallel to and adjoining the surface of attachment, while the long axis of the body of the young Cirriped is placed nearly at right angles to the surface of attachment. This change is connected with the ecdyses of the antennary apodemes (), which leave a deep bay on the ventral surface behind the peduncle. The chitinous skin of the Cirriped passes round the head of this bay, but on the moult of the pupa skin taking place becomes stretched out, owing to the posterior part of the larva bending dorsalwards. It is this flexure which causes the change in the position of the larva.


CRUSTACEA.


499


In addition to the remarkable external metamorphosis undergone during the pupa stage, a series of hardly less considerable internal changes take place, such as the atrophy of the muscles of the antennae, a change in the position of the stomach, etc.

Abdominalia. In the Alcippidae the larva leaves the egg as a Nauplius, and this stage is eventually followed by a pupa stage closely resembling that of the Thoracica. There are six pairs of thoracic natatory legs (Darwin, No. 519). Of these only the first and the last three are preserved in the adult, the first being bent forward in connection with the mouth. The body moreover partially preserves its segmentation, and the mantle does not secrete calcareous valves.

The very remarkable genus Cryptophialus, the development of which is described by Darwin (No. 519) in his classical memoir, is without a free Nauplius stage. The embryo is at first oval but soon acquires two anterior processes, apparently the first pair of antennae, and a posterior prominence, the abdomen. In a later stage the abdominal prominence disappears, and the antennary processes, within which the true antennas are now visible, are carried more towards the ventral surface. The larva next passes into the free Cypris stage, during which it creeps about the mantle cavity of its parent. It is enveloped in a bivalve shell, and the antennae have the normal cirriped structure. There are no other true appendages, but posteriorly three pairs of bristles are attached to a rudimentary abdomen. Paired compound eyes are present. During the succeeding pupa stage the metamorphosis into the adult form takes place, but this has not been followed out in detail.

In Kochlorine, a form discovered by Noll (No. 526) and closely related to Cryptophialus, the larvae found within the mantle represent apparently two larval stages, similar to two of the larval stages described by Darwin.

Rhizocephala. The Rhizocephala, as might have been antici


FIG. 233. STAGES IN THE DEVELOPMENT OF THE RHIZOCEPHALA. (From Huxley, after Fritz Miiller.)

A. Nauplius of Sacculina purpurea. B. Cypris stage of Lernseodiscus porcellanae. C. Adult of Peltogaster paguri.

II, III. IV. Two pairs of antennae and mandibles; cp. carapace; a. anterior end of body; b. generative aperture; c. root-like processes.


pated from their close relationship to Anelasma squalicola amongst the Thoracica, undergo a development differing much less from the type of the Thoracica than that of Cryptophialus and Kochlorine.

322


5oo


OSTRACODA.


Sacculina leaves the egg as a Nauplius (fig. 233 A), which differs from the ordinary type mainly (i) in the large development of an oval dorsal shield (eft] which projects far beyond the edge of the body, but is provided with the typical sternal horns, etc. ; and (2) in the absence of a mouth. The Cypris and pupa stages of Sacculina and other Rhizocephala (fig. 233 B) are closely similar to those of the Thoracica, but the paired eye is absent. The attachment takes place in the usual way, but the subsequent metamorphosis leads to the loss of the thoracic feet and generally to retrogressive changes.

OSTRACODA.

Our knowledge of the development of this remarkable group is entirely due to the investigations of Claus.

Some forms of Cythere are viviparous, and in the marine form Cypridina the embryo develops within the valves of the shell. Cypris attaches its eggs to water plants. The larvae of Cypris are free, and their development is somewhat complicated. The whole development is completed in nine ecdyses, each of them accompanied by more or less important changes in the constitution of the larva.

In the earliest free stage the larva has the characters of a true Nauplius with three pairs of appendages (fig. 234 A). The Nauplius presents howB A


-A'



MX SM


FlG. 234. TWO STAGES IN THE DEVELOPMENT OF CYPRIS. (From ChlUS.)

A. Earliest (Nauplius) stage. B. Second stage.

A'. A". First and second pairs of antennae ; Md. mandibles ; OL. labrum ; MX,', first pair of maxilla; /". first pair of feet.

ever one or two very marked secondary characters. In the first place it is completely enveloped in a fully formed bivalve shell, differing in unessential points from the shell of the adult. An adductor muscle (SM] for the shell is present. Again the second and third appendages, though locomotive in function are neither of them biramous, and the third one already contains a rudiment of the future mandibular blade, and terminates in an anteriorly directed hook-like bristle. The first pair of antenna? is moreover very similar to the second and is used in progression. Neither of the pairs of


CRUSTACEA.


501


antennae become much modified in the subsequent metamorphosis. The Nauplius has a single median eye, as in the adult Cypris, and a fully developed alimentary tract.

The second stage (fig. 234 B), inaugurated by the first moult, is mainly characterized by the appearance of two fresh pairs of appendages, viz. the first pair of maxillae and the first pair of feet ; the second pair of maxillae not being developed till later. The first pair appear as leaf-like curved



FIG. 235. STAGES IN THE DEVELOPMENT OF CYPRIS. (From Claus.)

A. Fourth stage. B. Fifth stage.

MX', first maxilla ; MX", and/', second maxilla ; /". first pair of feet ; L. liver.

plates (Mx'} more or less like Phyllopod appendages (Claus) though at this stage without an exopodite. The first pair of feet (/"} terminates in a curved claw and is used for adhering. The mandibles have by this stage fully developed blades, and have practically attained their adult form, consisting of a powerful toothed blade and a four-jointed palp.

During the third and fourth stages the first pair of maxillae acquire their pectinated gill plate (epipodite) and four blades ; and in the fourth stage (fig. 235 A) the second pair of maxillae (Mx"} arises, as a pair of curved plates, similar to the first pair of maxillae at their first appearance. The forked tail is indicated during the fourth stage by two bristles. During the fifth stage (fig. 235 B) the number of joints of the first pair of antennae becomes increased, and the posterior maxillae develop a blade and become


502


PHYLOGENY OF THE CRUSTACEA.


four-jointed ambulatory appendages terminating in a hook. The caudal fork becomes more distinct.

In the sixth stage (fig. 236) the second and hindermost pair of feet becomes formed (/"') and the maxillae of the second pair lose their ambulatory function, and begin to be converted into definite masticatory appendages by the reduced jointing of their palp, and the increase of their cutting blades. By the seventh stage all the appendages have practically attained their


Fu



FIG. 236. SIXTH STAGE IN THE DEVELOPMENT OF CYPRIS. (From Claus.) MX!, first maxilla ; Mx".f. second maxilla; /'. and/"', first and second pair oi feet ; Fu. caudal fork ; L. liver ; S.D. shell gland.

permanent form ; the second pair of maxillae has acquired small branchial plates, and the two following feet have become jointed. In the eighth and ninth stages the generative organs attain their mature form.

The larva of Cythere at the time of birth has rudiments of all the limbs, but the mandibular palp still functions as a limb, and the three feet (2nd pair of maxillae and two following appendages) are very rudimentary.

The larvae of Cypridina are hatched in a condition which to all intents and purposes resembles the adult.


Phylogeny of the Crustacea.

The classical work of Fritz Miiller (No. 452) on the phylogeny of the Crustacea has given a great impetus to the study of their larval forms, and the interpretations of these forms which he has offered have been the subject of a very large amount of criticism and discussion. A great step forward in this discussion has been recently made by Claus in his memoir (No. 448).

The most fundamental question concerns the meaning of the Nauplius. Is the Nauplius the ancestral form of the Crustacea, as is believed by Fritz Miiller and Claus, or are its peculiarities and constant occurrence due to some other cause ? The most plausible explanation on the second hypothesis


CRUSTACEA. 503


would seem to be the following. The segments with their appendages of Arthropoda and Annelida are normally formed from before backwards, therefore every member of these two groups with more than three segments must necessarily pass through a stage with only three segments, and the fact that in a particular group this stage is often reached on the larva being hatched is in itself no proof that the ancestor of the group had only three segments with their appendages. This explanation appears to me, so far as it goes, quite valid ; but though it relieves us from the necessity of supposing that the primitive Crustacea had only three pairs of appendages, it does not explain several other peculiarities of the Nauplius 1 . The more important of these are the following.

1. That the mandibles have the form of biramous swimming feet and are not provided with a cutting blade.

2. That the second pair of antennae are biramous swimming feet with a hook used in mastication, and are innervated (?) from the subcesophageal ganglion.

3. The absence of segmentation in the Nauplius body. An absence which is the more striking in that before the Nauplius stage is fully reached the body of the embryo is frequently divided into three segments, e.g. Copepoda and Cirripedia

4. The absence of a heart.

5. The presence of a median single eye as the sole organ of vision.

Of these points the first, second, and fifth appear only to be capable of being explained phylogenetically, while with reference to the absence of a heart it appears very improbable that the ancestral Crustacea were without a central organ of circulation. If the above positions are accepted the conclusion would seem to follow that in a certain sense the Nauplius is an ancestral form but that, while it no doubt had its three anterior pairs of appendages similar to those of existing Nauplii, it may perhaps have been provided with a segmented body behind provided with simple biramous appendages. A heart and cephalo-thoracic shield may also have been present, though the existence of the latter is perhaps doubtful. There was no doubt a median single eye, but it is difficult to decide whether or no paired compound eyes were also present. The tail ended in a fork between the prongs of which the anus opened ; and the mouth was protected by a large upper lip. In fact, it may very probably turn out that the most primitive Crustacea more resembled an Apus larva at the moult immediately before the appendages lose their Nauplius characters (fig. 208 B), or a Cyclops larva just before the Cyclops stage (fig. 229), than the earliest Nauplius of either of these forms.

If the Nauplius ancestor thus reconstructed is admitted to have existed, the next question in the phylogeny of the Crustacea concerns the relations of the various phyla to the Nauplius. Are the different phyla descended from the Nauplius direct, or have they branched at a later period from

1 For the characters of Nauplius vide p. 460.


504 PHYLOGENY OF THE CRUSTACEA.

some central stem? It is perhaps hardly possible as yet to give a full and satisfactory answer to this question, which requires to be dealt with for each separate phylum ; but it may probably be safely maintained that the existing Phyllopods are members of a group which was previously much larger, and the most central of all the Crustacean groups; and which more nearly retains in the characters of the second pair of antennae etc. the Nauplius peculiarities. This view is shared both by Claus and Dohrn, and appears to be in accordance with all the evidence we have both palaeontological and morphological. Claus indeed carries this view still further, and believes that the later Nauplius stages of the different Entomostracan groups and the Malacostraca (Penaeus larva) exhibit undoubted Phyllopod affinities. He therefore postulates the earlier existence of a Protophyllopod form, which would correspond very closely with the Nauplius as reconstructed above, from which he believes all the Crustacean groups to have diverged.

It is beyond the scope of this work to attempt to grapple with all the difficulties which arise in connection with the origin and relationships of the various phyla, but I confine myself to a few suggestions arising out of the developmental histories recorded above.

Malacostraca. In attempting to reconstitute from the evidence in our possession the ancestral history of the Malacostraca we may omit from consideration the larval history of all those types which leave the egg in nearly the adult form, and confine our attention to those types in which the larval history is most completely preserved.

There are three forms which are of special value in this respect, viz. Euphausia, Penaeus and Squilla. From the history of these which has already been given it appears that in the case of the Decapoda four stages (Claus) may be traced in the best preserved larval histories.

1. A Nauplius stage with the usual Nauplius characters.

2. A Protozoaea stage in which the maxillae and first pair of maxillipeds are formed behind the Nauplius appendages ; but in which the tail is still unsegmented. This stage is comparatively rarely preserved and usually not very well marked.

3. A Zoaea stage the chief features of which have already been fully characterised (vide p. 465). Three more or less distinct types of Zosea are distinguished by Claus. (a) That of Penaeus, in which the appendages up to the third pair of maxillipeds are formed, and the thorax and abdomen are segmented, the former being however very short. The heart is oval, with one pair of ostia. From this type the Zoaea forms of the other Decapoda are believed by Claus to be derived, (b} That of Euphausia, with but one pair of maxillipeds and those short and Phyllopod-like. The heart oval with one pair of ostia. (c) That of Squilla, with an elongated manychambered heart, two pairs of maxillipeds and the abdominal appendages in full activity.

4. A Mysis stage, which is only found in the macrurous Decapod larvie.

The embryological questions requiring to be settled concern the value


CRUSTACEA. 50$


of the above stages. Do they represent stages in the actual evolution of the present types, or have their characters been secondarily acquired in larval life ?

With reference to the first stage this question has already been discussed, and the conclusion arrived at, that the Nauplius does in a much modified form represent an ancestral type. As to the fourth stage there can be no doubt that it is also ancestral, considering that it is almost the repetition of an actually existing form.

The second stage can clearly only be regarded as an embryonic preparation for the third ; and the great difficulty concerns the third stage.

The natural view is that this stage like the others has an ancestral value, and this view was originally put forward by Fritz Miiller and has been argued for also by Dohrn. On the other hand the opposite side has been taken by Claus, who has dealt with the question very ably and at great length, and has clearly shewn that some of Fritz Miiller's positions are untenable. Though Claus' opinion is entitled to very great weight, an answer can perhaps be given to some of his objections. The view adopted in this section can best be explained by setting forth the chief points which Claus urges against Fritz Miiller's view.

The primary question which needs to be settled is whether the Malacostraca have diverged very early from the Nauplius root, or later in the history of the Crustacea from the Phyllopod stem. On this question Claus 1 brings arguments, which appear to me very conclusive, to shew that the Malacostraca are derived from a late Protophyllopod type, and Claus' view on this point is shared also by Dohrn. The Phyllopoda present so many characters (not possessed by the Nauplius) in common with the Malacostraca or their larval forms, that it is incredible that the whole of these should have originated independently in the two groups. The more important of these characters are the following.

1. The compound eyes, so often stalked in both groups.

2. The absence of a palp on the mandible, a very marked character of the Zoasa as well as of the Phyllopoda.

3. The presence of a pair of frontal sense knobs.

4. The Phyllopod character of many of the appendages. Cf. first pair of maxillipeds of the Euphausia Zosea.

1 Claus speaks of the various Crustacean phyla as having sprung from a Protophyllopod form, and it might be supposed that he considered that they all diverged from the same form. It is clear however from the context that he regards the Protophyllopod type from which the Malacostraca originated as far more like existing Phyllopods than that from which the Entomostracan groups have sprung. It is not quite easy to get a consistent view of his position on the question, since he states (p. 77) that the Malacostraca and the Copepods diverged from a similar form, which is represented in their respective developments by the Protozosea and earliest Cyclops stage. Yet if I understand him rightly, he does not consider the Protozosea stage to be the Protophyllopod stage from which the Malacostraca have diverged, but states on p. 71 that it was not an ancestral form at all.


506 PHYLOGENY OF THE CRUSTACEA.

5. The presence of gill pouches (epipodites) on many of the appendages 1 .

In addition to these points, to which others might be added, Claus attempts to shew that Nebalia must be regarded as a type intermediate between the Phyllopods and Malacostraca. This view seems fairly established, and if true is conclusive in favour of the Phyllopod origin of the Malacostraca. If the Protophyllopod origin of the Malacostraca is admitted, it seems clear that the ancestral forms of the Malacostraca must have developed their segments regularly from before backwards, and been provided with nearly similar appendages on all the segments. This however is far from the case in existing Malacostraca, and Fritz Miiller commences his summary of the characters of the Zoaea in the following words 2 . "The middle body with its appendages, those five pairs of feet to which these animals owe their name, is either entirely wanting or scarcely indicated." This he regards as an ancestral character of the Malacostraca, and is of opinion that their thorax is to be regarded as a later acquirement than the head or abdomen. Claus' answer on this point is that in the most primitive Zoasas, viz. those already spoken of as types, the thoracic and abdominal segments actually develop, in regular succession from before backwards, and he therefore concludes that the late development of the thorax in the majority of Zoaea forms is secondary and not an ancestral Phyllopod peculiarity.

This is the main argument used by Claus against the Zosea having any ancestral meaning. His view as to the meaning of the Zoaea may be gathered from the following passage. After assuming that none of the existing Zoaea types could have been adult animals, he says" Much more "probably the process of alteration of the metamorphosis, which the Mala" costracan phylum underwent in the course of time and in conjunction " with the divergence of the later Malacostracan groups, led secondarily " to the three different Zoaea configurations to which probably later modifica" tions were added, as for instance in the young form of the Cumaceae. We "might with the same justice conclude that adult Insects existed as cater" pillars or pupae as that the primitive form of the Malacostraca was a " Protozoaea or Zoaea."

Granting Claus' two main positions, viz. that the Malacostraca are derived from Protophyllopods, and that the segments were in the primary ancestral forms developed from before backwards, it does not appear impossible that a secondary and later ancestral form may have existed with a reduced thorax. This reduction may only have been partial, so that the Zoaea ancestor would have had the following form. A large cephalo-thorax and well-developed tail (?) with swimming appendages. The appendages up to the second pair of maxillipeds fully developed, but the thorax very

1 Claus appears to consider it doubtful whether the Malacostracan gills can be compared with the Phyllopod gill-pouches. 3 Facts for Darwin, p. 49.


CRUSTACEA. 507


imperfect and provided only with delicate foliaceous appendages not projecting beyond the edge of the cephalo-thoracic shield.

Another hypothesis for which there is perhaps still more to be said is that there was a true ancestral Zoaea stage in which the thoracic appendages were completely aborted. Claus maintains that the Zoaea form with aborted thorax is only a larval form ; but he would probably admit that its larval characters were acquired to enable the larva to swim better. If this much be admitted it is not easy to see why an actual member of the ancestral series of Crustacea should not have developed the Zoaea peculiarities when the mud-dwelling habits of the Phyllopod ancestors were abandoned, and a swimming mode of life adopted. This view, which involves the supposition that the five (or six including the third maxillipeds) thoracic appendages were lost in the adult (for they may be supposed to have been retained in the larva) for a series of generations, and reappeared again in the adult condition, at a later period, may at first sight appear very improbable, but there are, especially in the larval history of the Stomatopoda, some actual facts which receive their most plausible explanation on this hypothesis.

These facts consist in cases of the actual loss of appendages during development, and their subsequent reappearance. The two most striking cases are the following.

1. In the Erichthus form of the Squilla larva the appendages corresponding to the third pair of maxillipeds and first two pairs of ambulatory appendages of the Decapoda are developed in the Protozosea stage, but completely aborted in the Zoasa stage, and subsequently redeveloped.

2. In the case of the larva of Sergestes in the passage from the Acanthosoma (Mysis) stage to the Mastigopus stage the two hindermost thoracic appendages become atrophied and redevelop again later.

Both of these cases clearly fit in very well with the view that there was an actual period in the history of the Malacostraca in which the ancestors of the present forms were without the appendages which are aborted and redeveloped again in these larval forms. Claus' hypothesis affords no explanation of these remarkable cases.

It is however always possible to maintain that the loss and reappearance of the appendages in these cases may have no ancestral meaning ; and the abortion of the first pair of maxillipeds and reduction of some of the other appendages in the case of the Loricata is in favour of this explanation. Similar examples of the abortion and reappearance of appendages, which cannot be explained in the way attempted above, are afforded by the Mites and also by the Insects, e.g. Bees.

On the other hand there is almost a conclusive indication that the loss of the appendages in Sergestes has really the meaning assigned to it, in that in the allied genius Leucifer the two appendages in question are actually absent in the adult, so that the stage with these appendages absent is permanently retained in an adult form. In the absence of the mandibular palp in all the Zoaea forms, its actual atrophy in the Penaeus Zoasa, and its


508 PHYLOGENY OF THE CRUSTACEA.

universal reappearance in adult Malacostraca, are cases which tell in favour of the above explanation. The mandibular palp is permanently absent in Phyllopods, which clearly shews that its absence in the Zoaea stage is due to the retention of an ancestral peculiarity, and that its reappearance in the adult forms was a late occurrence in the Malacostracan history.

The chief obvious difficulty of this view is the redevelopment of the thoracic feet after their disappearance for a certain number of generations. The possibility of such an occurrence appears to me however clearly demonstrated by the case of the mandibular palp, which has undoubtedly been reacquired by the Malacostraca, and by the case of the two last thoracic appendages of Sergestes just mentioned. The above difficulty may be diminished if we suppose that the larvae of the Zoaea ancestors always developed the appendages in question. Such appendages might first only partially atrophy in a particular Zoaea form and then gradually come to be functional again ; so that, as a form with functional thoracic limbs came to be developed out of the Zoaea, we should find in the larval history of this form that the limbs were developed in the pre-zoaeal larval stages, partially atrophied in the Zoaea stage, and redeveloped in the adult. From this condition it would not be difficult to pass to a further one in which the development of the thoracic limbs became deferred till after the Zoaea stage.

The general arguments in favour of a Zoaea ancestor with partially or completely aborted thoracic appendages having actually existed in the past appear to me very powerful. In all the Malacostracan groups in which the larva leaves the egg in an imperfect form a true Zoaea stage is found. That the forms of these Zoaeas should differ considerably is only what might be expected, considering that they lead a free existence and are liable to be acted upon by natural selection, and it is probable that none of those at present existing closely resemble the ancestral form. The spines from their carapace, which vary so much, were probably originally developed, as suggested by Fritz Miiller, as a means of defence. The simplicity of the heart so different from that of Phyllopods in most forms of Zoaea is a difficulty, but the reduction in the length of the heart may very probably be a secondary modification ; the primitive condition being retained in the Squilla Zoaea. In any case this difficulty is not greater on the hypothesis of the Zoaea being an ancestral form, than on that of its being a purely larval one.

The points of agreement in the number and character of the appendages, form of the abdomen, etc. between the various types of Zoaea appear to me too striking to be explained in the manner attempted by Claus. It seems improbable that a peculiarity of form acquired by the larva of some ancestral Malacostracan should have been retained so permanently in so many groups l

1 A secondary larval form is less likely to be repeated in development than an ancestral adult stage, because there is always a strong tendency for the former, which is a secondarily intercalated link in the chain, to drop out by the occurrence of a reversion to the original type of development.


CRUSTACEA. 509


more permanently indeed than undoubtedly ancestral forms like that of Mysis and it would be still more remarkable that a Zoaea form should have been two or more times independently developed.

There are perhaps not sufficient materials to reconstruct the characters of the Zoaea ancestor, but it probably was provided with the anterior appendages up to the second pair of maxillipeds, and (?) with abdominal swimming feet. The heart may very likely have been many-chambered. Whether gill pouches were present on the maxillipeds and abdominal feet does not appear to me capable of being decided. The carapace and general shape were probably the same as in existing Zoaeas. It must be left an open question whether the six hindermost thoracic appendages were absent or only very much reduced in size.

On the whole then it may be regarded as probable that the Malacostraca are descended from Protophyllopod forms, in which, on the adoption of swimming habits, six appendages of the middle region of the body were reduced or aborted, and a Zoaea form acquired, and that subsequently the lost appendages were redeveloped in the descendants of these forms, and have finally become the most typical appendages of the group.

The relationship of the various Malacostracan groups is too difficult a subject to be discussed here, but it seems to me most likely that in addition to the groups with a Zoaea stage the Edriophthalmata and Cumaceae are also post-zoaeal forms which have lost the Zoasa stage. Nebalia is however very probably to be regarded as a prae-zoaeal form which has survived to the present day ; and one might easily fancy that its eight thin thoracic segments with their small Phyllopod-like feet might become nearly aborted.

Copepoda. The Copepoda certainly appear to have diverged very early from the main stem, as is shewn by their simple biramous feet and the retention of the median eye as the sole organ of vision. It may be argued that they have lost the eye by retrogressive changes, and in favour of this view cases of the Pontellidae and of Argulus may be cited. It is however more than doubtful whether the lateral eyes of the Pontellidae are related to the compound Phyllopod eye, and the affinities of Argulus are still uncertain. It would moreover be a great paradox if in a large group of Crustacea the lateral eyes had been retained in a parasitic form only (Argulus), but lost in all the free forms.

Cirripedia. The Cirripedia are believed by Claus to belong to the same phylum as the Copepoda. This view does not appear to be completely borne out by their larval history. The Nauplius differs very markedly from that of the Copepoda, and this is still more true of the Cypris stage. The Copepod-like appendages of this stage are chiefly relied upon to support the above view, but this form of appendages was probably very primitive and general, and the number (without taking into consideration the doubtful case of Cryptophialus) does not correspond to that in Copepoda. On the other hand the paired eyes and the bivalve shell form great difficulties in the way of Claus' view. It is clear that the Cypris stage represents more or less


510


PHYLOGENY OF THE CRUSTACEA.


closely an ancestral form of the Cirripedia, and that both the large bivalve shell and the compound eyes were ancestral characters. These characters would seem incompatible with Copepod affinities, but point to the independent derivation of the Cirripedia from some early bivalve Phyllopod form.

Ostracoda. The independent origin of the Ostracoda from the main Crustacean stem seems probable. Claus points out that the Ostracoda present by no means a simple organisation, and concludes that they were not descended from a form with a more complex organisation and a larger number of appendages. Some simplifications have however undoubtedly taken place, as the loss of the heart, and of the compound eyes in many forms. These simplifications are probably to be explained (as is done by Claus) as adaptations due to the small size of body and its enclosure in a thick bivalve shell. Although Claus is strongly opposed to the view that


I)



FIG. 737. FIGURES ILLUSTRATING THE DEVELOPMENT OF ASTACUS. (From Parker ; after Reichenbach.)

A. Section through part of the ovum during segmentation, n. nuclei ; w.y. white yolk ; y.p. yolk pyramids ; c. central yolk mass.

B and C. Longitudinal sections during the gastrula stage, a. archenteron ; b. blastopore ; ms. mesoblast ; ec. epiblast ; en. hypoblast distinguished from epiblast by shading.

I '. Highly magnified view of the anterior lip of blastopore to shew the origin of the primary mesoblast from the wall of the archenteron. p.ms. primary mesoblast ; ec. epiblast ; en. hypoblast.

I Two hypoblast cells to shew the amoeba-like absorption of yolk spheres. y. yolk ; . nucleus ; /. pseudopodial process.

F. Hypoblast cells giving rise endogenously to the secondary mesoblast (s.nts.). tt. nuclei.


CRUSTACEA. 5 1


the number of the appendages has been reduced, yet the very fact of the (in some respects) complex organisation of this group might seem to indicate that it cannot have diverged from the Phyllopod stem at so early a stage as (on Claus' view of the Nauplius) would seem to be implied by the very small number of appendages which is characteristic of it, and it therefore appears most probable that the present number may be smaller than that of the ancestral forms.

The formation of the germinal layers.

The formation of the germinal layers has been more fully studied in various Malacostraca, more especially in the Decapoda, than in other groups.

Decapoda. To Bobretzky (No. 472) is due the credit of having been the pioneer in this line of investigation ; and his researches have been followed up and enlarged by Haeckel, Reichenbach (No. 488), and Mayer (No. 482). The segmentation is centrolecithal and regular (fig. 237 A). At its close the blastoderm is formed of a single uniform layer of lens-shaped cells enclosing a central sphere of yolk, in which as a rule all trace of the division into columns, present during the earlier stages of segmentation, has disappeared ; though in Palaemon the columns remain for a long period distinct. The cells of the blastoderm are at first uniform, but in Astacus, Eupagurus, and most Decapoda, soon become more columnar for a small area, and form a circular patch. The whole patch either becomes at once invaginated (Eupagurus, Palaemon, fig. 239 A) or else the edge of it is invaginated as a roughly speaking circular groove deeper anteriorly than posteriorly, within which the remainder of the patch forms a kind of central plug, which does not become invaginated till a somewhat later period (Astacus, fig. 237 B and C). After the invagination of the above patch the remainder of the blastoderm cells form the epiblast.

The invaginated sack appears to be the archenteron and its mouth the blastopore. The mouth finally becomes closed 1 , and the sack itself then forms the mesenteron.

In Astacus the archenteron gradually grows forwards, its opening is at first wide, but becomes continuously narrowed

1 Bobretzky first stated that the invagination remained open, but subsequently corrected himself. Zeit. /. Wiss. Zool., Bd. xxiv. p. 186.


512


FORMATION OF THE LAYERS.



and is finally obliterated. Very shortly after this occurrence there is formed, slightly in front of the point where the last trace of the blastopore was observable, a fresh epiblastic invagination, which gives rise to the proctodaeum, and the opening of which remains as the definite anus. The proctodaeum (fig. 238 A, kg) is very soon placed in communication with the mesenteron (mg). The stomodaeum (fg) is formed during the same stage as the proctodaeum. It gives rise to the oesophagus and stomach. The hypoblast cells which form the wall of the archenteron grow with remarkable rapidity at the expense of the yolk ; the spherules of which they absorb and digest in an amceba-like fashion by means of their pseudopodia. They become longer and longer, and finally, after absorbing the whole yolk, acquire a form almost exactly similar to that of the yolk pyramids during segmentation (fig. 238 B). They enclose the cavity of the mesenteron, and their nuclei and protoplasm are situated externally. The cells of the mesenteron close to its junction with the proctodaeum differ from those elsewhere in being nearly flat.

In Palaemon (Bobretzky) the primitive invagination (fig. 239 A) has far smaller dimensions than in Astacus, and appears before the blastoderm cells have separated from the yolk pyramids. The cells which are situated at the bottom of it pass into the yolk, increase in number, and absorb the whole yolk, forming a solid mass of hypoblast in which the outlines of the individual cells would seem at first not to be distinct.



FlG. 238. TWO LONGITUDINAL SECTIONS OF THE EMBRYO OF ASTACUS.

(From Parker ; after Bobretzky.)

A. Nauplius stage. B. Stage after the hypoblast cells have absorbed the food yolk. The ventral surface is turned upwards, fg. stomodseum ; hg. proctodccum ; an. anus ; m. mouth ; mg. mesenteron ; abd. abdomen ; h. heart.

The blastopore in the mean


CRUSTACEA. 513

time becomes closed. Some of the nuclei now pass to the periphery of the yolk mass ; the cells appertaining to them gradually become distinct and assume a pyramidal form (fig. 239 B, hy\ the inner ends of the cells losing themselves in a central mass of yolk, in the interior of which nuclei are at first present but soon disappear. The mesenteron thus becomes constituted of a layer of pyramidal cells which merge into a central mass of yolk. Some of the hypoblast cells adjoining the junction of the proctodaeum and mesenteron become flattened, and in the neighbourhood of these cells a lumen



FlG. 239. TWO STAGES IN THE DEVELOPMENT OF PAL^MON SEEN IN SECTION.

(After Bobretzky.)

A. Gastrula stage.

B. Longitudinal section through a late stage, hy. hypoblast ; sg. supra-resophageal ganglion ; vg. ventral nerve cord ; hd. proctodseum ; st. stomodseum.

first appears. The stomodaeum and proctodaeum are formed as in Astacus. Fig. 239 B shews the relative positions of the proctodaeum, stomodaeum, and mesenteron. Although the process of formation of the hypoblast and mesenteron is essentially the same in Astacus and Palaemon, yet the differences between these two forms are very interesting, in that the yolk is external to the mesenteron in Astacus, but enclosed within it in Palaemon. This difference in the position of the yolk is rendered possible by the fact that the invaginated hypoblast cells in Palaemon do not, at first, form a continuous layer enclosing a central cavity, while they do so in Astacus.

The mesoblast appears to be formed of cells budded off from the anterior wall of the archenteron (Astacus, fig. 237 D), B. II. 33


514 FORMATION OF THE LAYERS.

or from its lateral walls generally (Palaemon). They make their first appearance soon after the imagination of the hypoblast has commenced. The mesoblast cells are at first spherical, and gradually spread, especially in an anterior direction, from their point of origin.

According to Reichenbach there are formed in Astacus at the Nauplius stage a number of peculiar cells which he speaks of as * secondary mesoblast cells.' His account is not very clear or satisfactory, but it appears that they originate (fig. 237 F) in the hypoblast cells by a kind of endogenous growth, and though they have at first certain peculiar characters they soon become indistinguishable from the remaining mesoblast cells.

Towards the end of the Nauplius period the secondary mesoblast cells aggregate themselves into a rod close to the epiblast in the median ventral line, and even bifurcate round the mouth and extend forwards to the extremity of the procephalic lobes. This rod of cells very soon vanishes, and the secondary mesoblast cells become indistinguishable from the primary. Reichenbach believes, on not very clear evidence, that these cells have to do with the formation of the blood.

General form of the body. The ventral thickening of epitlast or ventral plate, continuous with the invaginated patch already mentioned, forms the first indication of the embryo. It is at first oval, but soon becomes elongated and extended anteriorly into two lateral lobes the procephalic lobes. Its bilateral symmetry is further indicated by a median longitudinal furrow. The posterior end of the ventral plate next becomes raised into a distinct lobe the abdomen which in Astacus at first lies in front of the still open blastopore. This lobe rapidly grows in size, and at its extremity is placed the narrow anal opening. It soon forms a well-marked abdomen bent forwards over the region in front (figs. 239 B, and 240 A and B). Its early development as a distinct outgrowth causes it to be without yolk ; and so to contrast very forcibly with the anterior thoracic and cephalic regions of the body. In most cases this process corresponds to the future abdomen, but in some cases (Loricata) it appears to include part of the thorax. Before it has reached a considerable development, three pairs of appendages spring from the region of the head, viz. two pairs of antennae and the mandibles, and inaugurate a so-called Nauplius stage (fig. 240 A). These three appendages are formed nearly simultaneously, but the hindermost appears to become visible slightly before the two others


CRUSTACEA. 515


(Bobretzky). The mouth lies slightly behind the anterior pair of antennae, but distinctly in front of the posterior pair. The other appendages, the number of which at the time of hatching varies greatly in the different Decapods (vide section on larval development), sprout in succession from before backwards (fig. 240 B). The food yolk in the head and thoracic region gradually becomes reduced in quantity with the growth of the embryo, and by the time of hatching the disparity in size between the thorax and abdomen has ceased to exist.

Isopoda. The early embryonic phases of the Isopoda have been studied by means of sections by Bobretzky (No. 498) and Bullar (No. 499) and have been found to present considerable



FlG. 240. TWO STAGES IN THE DEVELOPMENT OF

A. Nauplius stage.

B. Stage with eight pairs of appendages, op. eyes ; at 1 , and at*, first and second antennae; md. mandibles; mx l , mx 2 . first and second maxillae; mxp*. third maxillipeds ; Ib. upper lip.

variations. When laid the egg is enclosed in a chorion, but shortly after the commencement of segmentation (Ed. van Beneden and Bullar) a second membrane appears, which is probably of the nature of a larval membrane.

In all the forms the segmentation is followed by the formation of a blastoderm, completely enclosing the yolk, and thickened along an area which will become the ventral surface of the embryo. In this area the blastoderm is formed of at least two layers of cells an external columnar epiblast, and an internal layer of scattered cells which form the mesoblast and probably in part also the hypoblast (Oniscus, Bobretzky ; Cymothoa, Bullar).

332


516 FORMATION OF THE LAYERS.

In Asellus aquaticus there is a centrolecithal segmentation, ending in the formation of a blastoderm, which appears first on the ventral surface and subsequently extends to the dorsal.

In Oniscus murarius, and Cymothoa the segmentation is partial [for its peculiarities and relationship vide p. 120] and a disc, formed of a single layer of cells, appears at a pole of the egg which corresponds to the future ventral surface (Bobretzky). This layer gradually grows round the yolk partly by division of its cells, though a formation of fresh cells from the yolk may also take place. Before it has extended far round the yolk, the central part of it becomes two or more layers deep, and the cells of the deeper layers rapidly increase in number, and are destined to give rise to the mesoblast and probably also to part or the whole of the hypoblast. In Cymothoa this layer does not at first undergo any important change, but in Oniscus it becomes very thick, and its innermost cells (Bobretzky) become imbedded in the yolk, which they rapidly absorb; and increasing in number first of all form a layer in the periphery of the yolk, and finally fill up the whole of the interior of the yolk (fig. 241 A), absorbing it in the process.

It appears possible that these cells do not, as Bobretzky believes, originate from the blastoderm, but from nuclei in the yolk which have escaped his observation. This mode of origin would be similar to that by which yolk cells originate in the eggs of the Insecta, etc. If Bobretzky's account is correct we must look to Palaemon, as he himself suggests, to find an explanation of the passage of the hypoblast cells into the yolk. The thickening of the primitive germinal disc would, according to this view, be equivalent to the invagination of the archenteron in Astacus, Palaemon, etc.

Whatever may be the origin of the cells in the yolk they no doubt correspond to the hypoblast of other types. In Cymothoa nothing similar to them has been met with, but the hypoblast has a somewhat different origin ; being apparently formed from some of the indifferent cells below the epiblast, which collect as a solid mass on the ventral surface, and then divide into two masses which become hollow and give rise to the liver caeca. Their fate, as well as that of the hypoblast in Oniscus, is dealt with in connection with the alimentary tract. The completion of the enclosure of the yolk by the blastoderm takes place on the dorsal surface. In all the Isopods which have been carefully


CRUSTACEA. 517


studied, there appears before any other organ a provisional structure formed from the epiblast and known as the dorsal organ. An account of it is given in connection with the development of the organs. The general external changes undergone by the larva in its development are as follows. The ventral thickened area of the blastoderm (ventral plate) shapes itself and girths nearly the whole circumference of the ovum in Oniscus (fig. 241 A) but is relatively much shorter in Cymothoa. Anteriorly it dilates into the two procephalic lobes. In Cymothoa it next becomes segmented; and the anterior segments are formed nearly simultaneously, and those of the abdomen somewhat later. At the same time a median depres


FlG. 241. TWO LONGITUDINAL SECTIONS THROUGH THE EMBRYO OF ONISCUS

MURARIUS. (After Bobretzky.)

st. stomodaeum ; pr. proctodseum ; hy. hypoblast formed of large nucleated cells imbedded in the yolk ; m. mesoblast ; vg. ventral nerve cord ; sg. supra- oesophageal ganglion ; li. liver ; do. dorsal organ ; zp. rudiment of masticatory apparatus ; ol. upper lip.

sion appears dividing the blastoderm longitudinally into two halves. The appendages are formed later than their segments, and the whole of them are formed nearly simultaneously, with the exception of the last thoracic, which does not appear till comparatively late after the hatching of the embryo. The late development of the seventh thoracic segment and appendage is a feature common to the majority of the Isopoda (Fritz Miiller). In Oniscus the limbs are formed in nearly the same way as in Cymothoa, but in Asellus they do not arise quite simultaneously. First of all, the two antennae and mandibles (the future palp) appear, inaugurating a stage often spoken of as the Nauplius stage, which is supposed to correspond with the free Nauplius


5l8 FORMATION OF THE LAYERS.

stage of Penaeus and Euphausia. At this stage a cuticle is shed (Van Beneden) which remains as an envelope surrounding the larva till the time of hatching. Similar cuticular envelopes are formed in many Isopoda. Subsequently the appendages of the thorax appear, and finally those of the abdomen. Later than the appendages there arise behind the mouth two prominences which resemble appendages, but give rise to a bilobed lower lip (Dohrn).

In Asellus and Oniscus the ventral plate moulds itself to the shape of the egg, and covers the greater part of the dorsal as well as of the ventral side (fig. 241 A). As a result of this the ventral surface of the embryo is throughout convex ; and in Asellus a deep fold appears on the back of the embryo, so that the embryo appears coiled up within the egg with its ventral side outwards and its head and tail in contact. In Oniscus the ventral surface is convex, but the dorsal surface is never bent in as in Asellus. In Cymothoa the egg is very big and the ventral plate does not extend nearly so far round to the dorsal side as in Asellus, in consequence of which the ventral surface is not nearly so convex as in other Isopoda. At the same time the telson is early formed, and is bent forwards so as to lie on the under side of the part of the blastoderm in front. In having this ventral curvature of the telson Cymothoa forms an exception amongst Isopods ; and in this respect is intermediate between the embryos of Asellus and those of the Amphipoda.

Amphipoda. Amongst the Amphipoda the segmentation is usually centrolecithal. In the case of Gammarus locusta (Ed. van Beneden and Bessels, No. 503) it commences with an unequal but total segmentation like that of the Frog (vide p. 97), and the separation of a central yolk mass is a late occurrence ; and it is noticeable that the part of the egg with the small segments eventually becomes the ventral surface. In the fresh-water species of Gammarus (G. pulex and fluviatilis) the segmentation is more like that of Insects ; the blastoderm cells being formed nearly simultaneously over a large part of the surface of the egg.

Both forms of segmentation give rise to a blastoderm covering the whole egg, which soon becomes thickened on the ventral


CRUSTACEA. 519


surface. There is formed, as in the Isopoda, a larval membrane at about the time when the blastoderm is completed. Very soon after this the egg loses its spherical shape, and becomes produced into a pointed extremity the future abdomen which is immediately bent over the ventral surface of the part in front. The ventral curvature of the hinder part of the embryo at so early an age stands in marked contrast to the usual condition of Isopod embryos, and is only approached in this group, so far as is known, in the case of Cymothoa.

At the formation of the first larval membrane the blastoderm cells separate themselves from it, except at one part on the dorsal surface. The patch of cells adherent at this part gives rise to a dorsal organ, comparable with that in Oniscus, connecting the embryo and its first larval skin. A perforation appears in it at a later period.

The segments and limbs of the Amphipoda are all formed before the larva leaves the egg.

Cladocera. The segmentation (Grobben, No. 455) takes place on the normal centrolecithal type, but is somewhat unequal. Before the close of the segmentation there may be seen at the apex of the vegetative pole one cell marked off from the remainder by its granular aspect. It gives rise to the generative organs. One of the cells adjoining it gives rise to the hypoblast, and the other cells which surround it form the commencement of the mesoblast. The remaining cells of the ovum form the epiblast. By a later stage the hypoblast cell is divided into thirty-two cells and the genital cell into four, while the mesoblast forms a circle of twelve cells round the genital mass.

The hypoblast soon becomes involuted ; the blastopore probably closes, and the hypoblast forms a solid cord of cells which eventually becomes the mesenteron. The stomodaeum is said to be formed at the point of closure of the blastopore. The mesoblast passes inwards and forms a mass adjoining the hypoblast, and somewhat later the genital mass also becomes covered by the epiblast. The proctodseum appears to be formed later than the stomodasum.

The embryo as first shewn by Dohrn passes through a Nauplius stage in the brood-pouch, but is hatched, except in the case of the winter eggs of Leptodora, in a form closely resembling the adult.

Copepoda. Amongst the free Copepoda the segmentation and formation of the layers have recently been investigated by Hoek (No. 512). He finds that there is, in both the fresh-water and marine forms studied by him, a centrolecithal segmentation similar to that of Palaemon and Pagurus (vide p. 112), which might from the surface be supposed to be


520 FORMATION OF THE LAYERS.

complete and nearly regular. After the formation of the blastoderm an invagination of some of its cells takes place and is completed in about a quarter of an hour. The opening becomes closed. This invagination is compared by Hoek to the invagination in Astacus, and is believed by him to give rise to the mesenteron. Its point of closing corresponds with the hind end of the embryo. On the ventral surface there appear two transverse furrows dividing the embryo into three segments, and a median longitudinal furrow which does not extend to the front end of the foremost segment. The three pairs of Nauplius appendages and upper lip become subsequently formed as outgrowths from the sides of the ventral blastodermic thickening.

Amongst the parasitic Copepoda there are found two distinct types of segmentation, analogous to those in the Isopoda. In the case of Condracanthus the segmentation is somewhat irregular, but on the type of Eupagurus, etc. (vide p. 112). In the other group (Anchorella, Clavella, Congericola, Caligus, Lerneopoda) the segmentation nearly resembles the ordinary meroblastic type (vide p. 120), and is to be explained in the same manner as in the cases of Oniscus and Cymothoa. The first blastodermic cells sometimes appear in a position corresponding with the head end of the embryo (Anchorella), at other times at the hind end (Clavella), and sometimes in the middle of the ventral surface. The dorsal surface of the yolk is always the latest to be inclosed by the blastoderm cells. A larval cuticle similar to that of the Isopoda is formed at the same time as the blastoderm. At the sides of the ventral thickening of the blastoderm there grow out the Nauplius appendages, of which only the first two appear in Anchorella. In Anchorella and Lerneopoda the embryos are not hatched at the Nauplius stage, but after the Nauplius appendages have been formed a fresh cuticle the Nauplius cuticle is shed, and within it the embryo develops till it reaches the so-called Cyclops stage (vide p. 490). The embryo within the egg has its abdomen curved dorsalwards as amongst the Isopoda.

Cinipedia. The segmentation of Balanus and Lepas commences by the segregation of the constituents of the egg into a more protoplasmic portion, and a portion formed mainly of food material. The former separates from the latter as a distinct segment, and then divides into two not quite equal portions. The division of the protoplasmic part of the embryo continues, and the resulting segments grow round the single yolk segment. The point where they finally enclose it is situated on the ventral surface (Lang) at about the position of the mouth (?).

After being enclosed by the protoplasmic cells the yolk divides, and gives rise to a number of cells, which probably supply the material for the walls of the mesenteron. The external layer of protoplasm forms the so-called blastoderm, and soon (Arnold, Lang) becomes thickened on the dorsal surface.

The embryo is next divided by two constrictions into three segments ; and there are formed the three appendages corresponding to these, which are


CRUSTACEA. 52!


at first simple. The two posterior soon become biramous. The larva leaves the egg before any further appendages become formed.

Comparative development of the organs.

Central nervous system. The ventral nerve cord of the Crustacea develops as a thickening of the epiblast along the median ventral line ; the differentiation of which commences in front, and thence extends backwards. The ventral cord is at first unsegmented. The supra-oesophageal ganglia originate as thickenings of the epiblast of the procephalic lobes.

The details of the above processes are still in most cases very imperfectly known. The fullest account we have is that of Reichenbach (No. 488) for Astacus. He finds that the supra- cesophageal ganglia and ventral cord arise as a continuous formation, and not independently as would seem to be the case in Chsetopoda. The supra-cesophageal ganglia are formed from the procephalic lobes. The first trace of them is visible in the form of a pair of pits, one on each side of the middle line. These pits become in the Nauplius stage very deep, and their walls are then continued into two ridges where the epiblast is several cells deep, which pass backwards one on each side of the mouth. The walls of the pits are believed by Reichenbach to give rise to the optic portions of the supra-cesophageal ganglia, and the epiblastic ridges to the remainder of the ganglia and to the circum-cesophageal commissures. At a much later stage, when the ambulatory feet have become formed, a median involution of epiblast in front of the mouth and between the two epiblast ridges gives rise to a central part of the supracesophageal ganglia. Five elements are thus believed by Reichenbach to be concerned in the formation of these ganglia, viz. two epiblast pits, two epiblast ridges, and an involution of epiblast between the latter. It should be noted however that the fate neither of the pair of pits, nor of the median involution, appears to have been satisfactorily worked out. The two epiblast ridges, which pass back from the supra-cesophageal ganglia on each side of the mouth, are continued as a pair of thickenings of the epiblast along the sides of a median ventral groove. This groove is deep in front and shallows out posteriorly. The thickenings on the sides of this groove no doubt give rise to the lateral halves of the ventral cord, and the cells of the groove itself are believed by Reichenbach, but it appears to me without sufficient evidence, to become invaginated also and to assist in forming the ventral cord. When the ventral cord becomes separated from the epiblast the two halves of it are united in the middle line, but it is markedly bilobed in section.

In the Isopoda it would appear both from Bobretzky's and Bullar's observations that the ventral nerve cord arises as an unpaired thickening of the epiblast in which there is no trace of anything like a median involution. After this thickening has become separated from the epiblast a slight


522 DEVELOPMENT OF ORGANS.

median furrow indicates its constitution out of two lateral cords. The supra-oesophageal ganglia are stated to be developed quite simply as a pair of thickenings of the procephalic lobes, but whether they are from the first continuous with the ventral cord does not appear to have been determined.

The later stages in the differentiation of the ventral cord are, so far as is known, very similar throughout the Crustacea. The ventral cord is, as has been stated, at first unsegmented (fig. 241 A, vg\ but soon becomes divided by a series of constrictions into as many ganglia as there are pairs of appendages or segments (fig. 241 B, vg).

There appears either on the ventral side (Oniscus) or in the centre (Astacus, Palaemon) of the two halves of each segment or ganglion a space filled with finely punctuated material, which is the commencement of the commissural portion of the cords. The commissural tissue soon becomes continuous through the length of the ventral cord, and is also prolonged into the supracesophageal ganglia.

After the formation of the commissural tissue the remaining cells of the cord form the true ganglion cells. A gradual separation of the ganglia next takes place, and the cells become confined to the ganglia, which are finally only connected by a double band of commissural tissue. The commissural tissue not only gives rise to the longitudinal cords connecting the successive ganglia, but also to the transverse commissures which unite the two halves of the individual ganglia.

The ganglia usually, if not always, appear at first to correspond in number with the segments, and the smaller number so often present in the adult is due to the coalescence of originally distinct ganglia.

Organs of special sense. Comparatively little is known on this head. The compound eyes are developed from the coalescence of two structures, both however epiblastic, viz. (i) part of the superficial epiblast of the procephalic lobes ; (2) part of the supra-cesophageal ganglia. The former gives rise to the corneal lenses, the crystalline cones, and the pigment surrounding them ; the latter to the rhabdoms and the cells which encircle them. Between these two parts a mesoblastic pigment is interposed.


CRUSTACEA.


523


Of the development of the auditory and olfactory organs almost nothing is known.

Dorsal organ. In a considerable number of the Malacostraca and Branchiopoda a peculiar organ is developed from the epiblast in the anterior dorsal region. This organ has been called the dorsal organ. It appears to be of a glandular nature, and is usually very large in the embryo or larva and disappears in the adult ; but in some Branchiopoda it persists through life. In most cases it is unpaired, but in some instances a paired organ appears to take its place.

Various views as to its nature have been put forward. There is but little doubt of its being glandular, and it is possible that it is a provisional renal organ, though so far as I know concretions have not yet been found in it.

Its development has been most fully studied in the Isopoda.

In Cymothoa (Bullar, No. 499) there appears on the dorsal surface, in the region which afterwards becomes the first thoracic segment, an unpaired linear thickening of the blastoderm. This soon becomes a circular patch, the central part of which is invaginated so as to communicate with the exterior by a narrow opening only (fig. 242). It becomes at the same time attached to the inner egg membrane. It retains this condition till the close of larval life.

In Oniscus (Dohrn, No. 500 ; Bobretzky, No. 498) there appears very early a dorsal patch of thickened cells. These cells become attached at their edge to the inner egg membrane and gradually separated from the embryo, with which they finally only re- , FlG - W- DIAGRAMMATIC SECTION OF . , ... CYMOTHOA SHEWING THE DORSAL ORGAN. main in connection by a hollow (F rom Bullar.)

column of cells (fig. 241 A, do).

The original patch now gradually spreads over the inner egg membrane, and forms a transverse saddle-shaped band of flattened cells which engirths the embryo on all but the ventral side.

In the Amphipods the epiblast cells remain attached for a small area on the dorsal surface to the first larval skin, when this is formed. This patch of cells, often spoken of as a micropyle apparatus, forms a dorsal organ equivalent to that in Oniscus. A perforation is formed in it at a later



524


DEVELOPMENT OF ORGANS.


period. A perhaps homologous structure is found in the embryos of Euphausia, Cuma, etc.

In many Branchiopoda a dorsal organ is found. Its development has been studied by Grobben in Moina. It persists in the adult in Branchipus, Limnadia, Estherea, etc.

In the Copepoda a dorsal organ is sometimes found in the embryo ; Grobben at any rate believes that he has detected an organ of this nature in the embryo of Cyclops serrulatus.

A paired organ which appears to be



FIG. 243. DIAGRAMMATIC SECTION OF AN EMBRYO OF ASELLUS AQUATICUS TO SHEW THE PAIRED DORSAL ORGAN. (From Bullar ; after E. van Beneden.)


of the same nature has been found in Asellus and Mysis.

In Asellus (Rathke (No. 501), Dohrn (No. 500), Van Beneden (No. 497)) this organ originates as two cellular masses at the sides of the body just behind the region of the procephalic lobes. Each of them becomes trifoliate and bends towards the ventral surface. In each of their lobes a cavity arises and finally the three cavities unite, forming a trilobed cavity open to the yolk. This organ eventually becomes so large that it breaks through the egg membranes and projects at the sides of the embryo (fig. 243\ Though formed before the appendages it does not attain its full development till considerably after the latter have become well established.

In Mysis it appears during the Nauplius stage as a pair of cavities lined by columnar cells, which atrophy very early.

Various attempts have been made to identify organs in other Arthropod embryos with the dorsal organ of the Crustacea, but the only organ at all similar which has so far been described is one found in the embryo of Linguatula (vide Chapter XIX.), but there is no reason to think that this organ is really homologous with the dorsal organ of the Crustacea.


The mesoblast. The mesoblast in the types so far investigated arises from the same cells as the hypoblast, and appears as a somewhat irregular layer between the epiblast and the hypoblast. It gives rise to the same parts as in other forms, but it is remarkable that it does not, in most Decapods and Isopods


CRUSTACEA. 525


(and so far we do not know about other forms), become divided into somites, at any rate with the same distinctness that is usual in Annelids and Arthropods. Not only so, but there is at first no marked division into a somatic and splanchnic layer with an intervening body cavity. Some of the cells become differentiated into the muscles of the body wall and limbs ; and other cells, usually in the form of a very thin layer, into the muscles of the alimentary tract. In the tail of Palcsmon Bobretzky noticed that the cells about to form the muscles of the body were imperfectly divided into cubical masses corresponding with the segments ; which however, in the absence of a central cavity, differed from typical mesoblastic somites. In Mysis Metschnikoff states that the mesoblast becomes broken up into distinct somites. Further investigations on this subject are required. The body cavity has the form of irregular blood sinuses amongst the internal organs.

Heart. The origin and development of the heart and vascular system are but very imperfectly known.

In Phyllopods (Branchipus) Claus (No. 454) has shewn that the heart is formed by the coalescence of the lateral parts of the mesoblast of the ventral plates. The chambers are formed successively as the segments to which they belong are established, and the anterior chambers are in full activity while the posterior are not yet formed.

In Astacus and Palaemon, Bobretzky finds that at the stage before the heart definitely appears there may be seen a solid mass of mesoblast cells in the position which it eventually occupies 1 ; and considers it probable that the heart originates from this mass. At the time when the heart can first be made out and before it has begun to beat, it has the form of an oval sack with delicate walls separated from the mesenteron by a layer of splanchnic mesoblast. Its cavity is filled with a peculiar plasma which also fills up the various cavities in the mesoblast. Around it a pericardial sack is soon formed, and the walls of the heart become greatly thickened. Four bands pass off from the heart, two dorsalwards which become fixed to the integument, and two ventralwards. There is also a median band of cells connecting the heart with the dorsal integument. The main arteries arise as direct prolongations of the heart. Dohrn's observations on Asellus greatly strengthen the view that the heart originates from a solid mesoblastic mass, in that he was able to observe the hollowing out of the mass in

1 Reichenbach describes these cells, and states that there is a thickening of the epiblast adjoining them. In one place he states that the heart arises from this thickening of epiblast, and in another that it arises from the mesoblast. An epiblastic origin of the heart is extremely improbable.


526 DEVELOPMENT OF ORGANS.

the living embryo (cf. the development of the heart in Spiders). Some of the central cells (nuclei, Dohrn) become blood corpuscles. The formation of these is not, according to Dohrn, confined to the heart, but takes place in situ in all the parts of the body (antennae, appendages, etc.). The corpuscles are formed as free nuclei and are primarily derived from the yolk, which at first freely communicates with the cavities of the appendages.

Alimentary tract. In Astacus the formation of the mesenteron by invagination, and the absorption of the yolk by the hypoblast cells, have already been described. On the absorption of the yolk the mesenteron has the form of a sack, the walls of which are formed of immensely long cells the yolk pyramids at the base of which the nucleus is placed (fig. 238 B). This sack gives rise both to the portion of the alimentary canal between the abdomen and the stomach and to the liver. The epithelial wall of both of these parts is formed by the outermost portions of the pyramids with the nuclei and protoplasm becoming separated off from the yolk as a layer of flat epithelial cells. The yolk then breaks up and forms a mass of nutritive material filling up the cavity of the mesenteron.

The differentiation both of the liver and alimentary tract proper first takes place on the ventral side, and commences close to the point where the proctodasum ends, and extends forward from this point. A layer of epithelial cells is thus formed on the ventral side of the mesenteron which very soon becomes raised into a series of longitudinal folds, one of which in the middle line is very conspicuous. The median fold eventually, by uniting with a corresponding fold on the dorsal side, gives rise to the true mesenteron ; while the lateral folds form parallel hepatic cylinders, which in front are not constricted off from the alimentary tract. The lateral parts of the dorsal side of the mesenteron similarly give rise to hepatic cylinders. The yolk pyramids of the anterior part of the mesenteron, which projects forwards as a pair of diverticula on each side to the level of the stomach, are not converted into hepatic cylinders till after the larva is hatched.

The proctodasum very early opens into the mesenteron, but the stomodaeum remains closed till the differentiation of the mid-gut is nearly completed. The proctodaeum gives rise to the abdominal part of the intestine, and the stomodaeum to the oesophagus and stomach. The commencement of the masticatory apparatus in the latter appears very early as a dorsal thickening of the epithelium.

The primitive mesenteron in Palaemon differentiates itself into the permanent mid-gut and liver in a manner generally similar to that in Astacus, though the process is considerably less complicated. A distinct layer of cells separates itself from the outer part of the yolk pyramids, and gives rise to the glandular lining both of the mid-gut and of the liver. The differentiation of this layer commences behind, and the mid-gut very soon communicates freely with the proctodasum. The lateral parts of the primitive mesenteron become constricted into four wings, two directed forwards and two backwards ; these, after the yolk in them has become absorbed, constitute the liver. The median part simply becomes the me


CRUSTACEA. 527


senteron. The stomachic end of the stomodaeum lies in contact with the mesenteron close to the point where it is continued into the hepatic diverticula, and, though the partition-wall between the two becomes early very thin, a free communication is not established till the yolk has been completely absorbed.

The alimentary tract in the Isopoda is mainly if not entirely formed from the proctodaeum and stomodaeum, both of which arise before any other part of the alimentary system as epiblastic invaginations, and gradually grow inwards (fig. 244). In Oniscus the liver is formed as two discs at the surface of the yolk on each side of the anterior part of the body. Their walls are composed of cubical cells derived from the yolk cells, the



pr

s r " a qcaggaw. rt -j_ .-. f .i~T' : . -^a^Mi^ . - .. >va^^^

Vff

FlG. 244. TWO LONGITUDINAL SECTIONS THROUGH THE EMBRYO OF ONISCUS

MURARIUS. (After Bobretzky.)

st. stomodaeum ; pr. proctodseum ; hy. hypoblast formed of large nucleated cells imbedded in yolk ; m. mesoblast ; vg. ventral nerve cord ; jr^. supra- oesophageal ganglion ; li. liver; do. dorsal organ; zp. rudiment of masticatory apparatus.

origin of which was spoken of on p. 516. These two discs gradually take the form of sacks (fig. 244 B, li.) freely open on their inner side to the yolk. As these sacks continue to grow the stomodaeum and proctodaeum do not remain passive. The stomodaeum, which gives rise to the oesophagus and stomach of the adult, soon exhibits a posterior dilatation destined to become the stomach, on the dorsal wall of which a well-marked prominence the earliest trace of the future armature is soon formed (fig. 244 B, xp}. The proctodaeum (pr) grows with much greater rapidity than the stomodaeum, and its end adjoining the yolk becomes extremely thin or even broken through. In the earliest stages it was surrounded by the yolk cells, but in its later growth the yolk cells become gradually reduced in number and appear to recede before it so much so that one is led to conclude that the later growth of the proctodaeum takes place at the expense of the yolk cells.

The liver sacks become filled with a granular material without a trace of cells ; their posterior wall is continuous with the yolk cells, and their anterior lies close behind the stomach. The proctodaeum continually grows forwards till it approaches close to the stomodaeum, and the two


528 DEVELOPMENT OF ORGANS.

liver sacks, now united into one at their base, become directly continuous with the proctodaeum. By the stage when this junction is effected the yolk cells have completely disappeared. It seems then that in Oniscus the yolk cells (hypoblast) are mainly employed in giving rise to the walls of the liver ; but that they probably also supply the material for the later growth of the apparent proctodaeum. It becomes therefore necessary to conclude that the latter, which might seem, together with the stomodasum, to form the whole alimentary tract, does in reality correspond to the proctodaeum and mesenteron together, though the digestive fluids are no doubt mainly secreted not in the mesenteron but in the hepatic diverticula. The proctodaeum and stomodaeum at first meet each other without communicating, but before long the partition between the two is broken through.

In Cymothoa (Bullar, No. 499) the proctodaeum and stomodaeum develop in the same manner as in Oniscus, but the hypoblast has quite a different form. The main mass of the yolk, which is much greater than in Oniscus, is not contained in definite yolk cells, but the hypoblast is represented by (i) two solid masses of cells, derived apparently from the inner layer of blastoderm cells, which give rise to the liver ; and (2) by a membrane enclosing the yolk in which nuclei are present.

The two hepatic masses lie on the surface of the yolk, and each of them becomes divided into three short caecal tubes freely open to the yolk. The stomodaeum soon reaches its full length, but the proctodaeum grows forwards above the yolk till it meets the stomodaeum. By the time this takes place the liver caeca have grown into three large tubes filled with fluid, and provided with a muscular wall. They now lie above the yolk, and no longer communicate directly with the cavity of the yolk sack, but open together with the yolk sack into the point of junction of the proctodaeum and stomodaeum. The yolk sack of Cymothoa no doubt represents part of the mesenteron, but there is no evidence in favour of any part of the apparent proctodaeum representing it also, though it is quite possible that it may do so. The relations of the yolk sack and hepatic diverticula in Cymothoa appear to hold good for Asellus and probably for most Isopoda.

The differences between the Decapods and Isopods in the development of the mesenteron are not inconsiderable, but they are probably to be explained by the relatively larger amount of food yolk in the latter forms. The solid yolk in the Isopods on this view represents the primitive mesenteron of Decapods after the yolk has been absorbed by the hypoblast cells. Starting from this standpoint we find that in both groups the lateral parts of the mesenteron become the liver. In Decapods the middle part becomes directly converted into the mid-gut, the differentiation of it commencing behind and proceeding forwards. In the Isopods, owing to the mesenteron not having a distinct cavity, the differentiation of it, which proceeds forwards as in Decapods, appears simply like a prolongation forwards of the proctoda?um, the cells for the prolongation being probably supplied from the yolk. In Cymothoa the food yolk is so bulky that a special yolk sack is developed


CRUSTACEA.


529


for its retention, which is not completely absorbed till some time after the alimentary canal has the form of a continuous tube. The walls of this yolk sack are morphologically a specially developed part of the mesenteron.

BIBLIOGRAPHY.

General Works.

(447) C. Spence Bate. " Report on the present state of our knowledge of the Crustacea." Report of the British Association for 1878.

(448) C. Claus. Untersuchungen zur Erforschung der genealogischen Grundlage des Crustaceen- Systems. Wien, 1876.

(449) A. Dohrn. "Geschichte des Krebsstammes. " Jenaische Zeitschrift, Vol. VI. 1871.

(450) A. Gerstaecker. Bronris Thierreich, Bd. v. Arthropoda, 1866.

(451) Th. H. Huxley. The Anatomy of Invertebrated Animals. London, 1877.

(452) Fritz Mliller. Fur Darwin, 1864. Translation, Facts for Darwin. London, 1869.

Branchiopoda.

(453) Brauer. "Vorlaufige Mittheilung iiber die Entwicklung u. Lebensweise des Lepidurus (Apus) productus." Sitz. der Ak. d. Wiss. Wien, Vol. LXIX., 1874.

(454) C. Claus. "Zur Kenntniss d. Baues u. d. Entwicklung von Branchipus stagnalisu. Apus cancriformis." Abh. d. kb'nig. Gesell. der Wiss. Gb'ttingen, Vol. XVIII. 1873.

(455) C. Grobben. "Zur Entwicklungsgeschichte d. Moina rectirostris." Arbeit, a. d. zoologisch. Institute Wien, Vol. II., 1879.

(456) E. Grube. " Bemerkungen uber die Phyllopoden nebst einer Uebersicht etc." Archivf. Naturgeschichte, Vol. xix., 1853.

(457) N. Joly. " Histoire d'un petit Crustace (Artemia salina, Leach} etc." Annales d. Sciences Natur., 2nd ser., Vol. xiii., 1840.

(458) N. Joly. " Recherches zoologiques anatomiques et physiologiques sur 1'Isaura cycladoides ( = Estheria) nouveau genre, etc." Annales d. Sciences Nat., 2nd ser., Vol. xvii., 1842.

(459) Lereboullet. " Observations sur la generation et le developpement de la Ltmnadia de Hermann." Annales d. Sciences Natur., <$th ser., Vol. v., 1866.

(460) F. Leydig. " Ueber Artemia salina u. Branchipus stagnalis." Zeit. f. wiss. ZooL, Vol. in., 1851.

(461) G. O. Sars. " Om en dimorph Udvikling samt Generationsvexel hos Leptodora." Vidensk. Selskab. Forhand, 1873.

(462) G. Zaddach. De apodis cancreformis Schaeff. anatome et historia evolutionis. Dissertatio inanguralis zootomica. Bonnse, 1841.

Nebaliadce.

(463) C. Claus. " Ueber den Bau u. die systematische Stellung von Nebalia." Zeit.f. wiss. Zool., Bd. xxn. 1872.

(464) E. Metschnikoff. Development of Nebalia (Russian), 1868.

B. II. 34


530 BIBLIOGRAPHY.


Schizopoda.

(465) E. van Beneden, " Recherches sur 1'Embryogenie des Crustaces. n. DeVeloppement des Mysis." Bullet, de rAcadtmie roy. de Belgique, second series, Tom. xxvin. 1869.

(46G) C. Glaus. " Ueber einige Schizopoden u. niedere Malakostraken." Zett. f. wiss. Zoologie, Bd. XII I., 1863.

(467) A. Dohrn. " Untersuchungen Ub. Bau u. Entwicklung d. Arthropoden." Zeit.f. wiss. Zool.y Bd. XXL, 1871, .p. 375. Peneus zoaea (larva of Euphausia).

(468) E. Metschnikoff. " Ueber ein Larvenstadium von Euphausia." Zeit. fiir wiss. Zool., Bd. xix., 1869.

(469) E. Metschnikoff. " Ueber den Naupliuszustand von Euphausia. " Zeit. fiir wiss. Zool., Bd. XXI., 1871.

Decapoda.

(470) S pence Bate. "On the development of Decapod Crustacea." Phil. Trans., 1858.

(471) Spence Bate. " On the development of Pagurus." Ann. and Mag. Nat. History, Series 4, Vol. II., 1868.

(472) N. Bobretzky. Development of Astacus and Palamon. Kiew, 1873. (Russian.)

(473) C. Glaus. "Zur Kenntniss d. Malakostrakenlarven. " Wiirzb. naturw. Zeitschrift, 1861.

(474) R. Q. Couch. "On the Metamorphosis of the Decapod Crustaceans." Report Cornwall Polyt. Society. 1848.

(475) Du Cane. "On the Metamorphosis of Crustacea." Ann. and Mag. of Nat. History, 1839.

(476) Walter Faxon. " On the development of Palsemonetes vulgaris." Bull, of the Mus. of Camp. Anat. Harvard, Cambridge, Mass., Vol. v., 1879.

(477) A. Dohrn. " Untersuchungen lib. Bau u. Entwicklung d. Arthropoden." " Zur Entwicklungsgeschichte der Panzerkrebse. Scyllarus Palinurus." Zeit. f. wiss. Zool., Bd. xx., 1870.

(478) A. Dohrn. "Untersuchungen lib. Bau u. Entwicklung d. Arthropoden. Erster Beitrag z. Kenntniss d. Malacostraken u. ihrer Larven Amphion Reynaudi, Lophogaster, Portunus, Porcellanus, Elaphocaris. " Zeit. f. wiss. Zool., Bd. xx., 1870.

(479) A. Dohrn. "Untersuchungen lib. Bau u. Entwicklung d. Arthropoden. Zweiter Beitrag, etc." Zeit.f. wiss. Zool., Bd. xxi., 1871.

(480) N. Joly. " Sur la Caridina Desmarestii." Ann. Scien. Nat., Tom. xix., 1843.

(481) Lereboullet. " Recherches d . 1'embryologie comparee sur le developpement du Brochet, de la Perche et de 1'Ecrevisse." Mem. Savans ktrang. Paris, Vol. xvn., 1862.

(482) P. Mayer. "Zur Entwicklungsgeschichte d. Dekapoden." Jenaische Zeitschrift, Vol. XI., 1877.

(483) F r i t z M u 1 1 e r. " Die Verwandlung der Porcellana." Archivf. Natnrgeschichte, 1862.


CRUSTACEA. 531


(484) Fritz Muller. " Die Verwandlungen d. Garneelen," Archiv f. Naturgesch., Tom. xxix.

(485) Fritz Muller. " Ueber die Naupliusbrut d. Garneelen." Zeit f. wiss. Zool., Bd. xxx., 1878.

(486) T. J. Parker. "An account of Reichenbach's researches on the early development of the Fresh-water Crayfish." Quart. J. of M. Science, Vol. xvin., 1878.

(487) H. Rathke. Ueber die Bildung u. Entivicklung d. Flusskrebses. Leipzig, 1829.

(488) H. Reichenbach. " Die Embryoanlage u. erste Entwicklung d. Flusskrebses." Zeit.f. wiss. Zool., Vol. xxix., 1877.

(489) F. Richters. " Ein Beitrag zur Entwicklungsgeschichte d. Loricaten." Zeit.f. wiss. Zool., Bd. xxiil., 1873.

(490) G. O. Sars. " Om Hummers posiembryonale Udvikling. " Vidensk Selsk. Fork. Christiania, 1874.

(491) Sidney J. Smith. " The early stages of the American Lobster. " Trans, of the Connecticut Acad. of Arts and Sciences, Vol. n., Part 2, 1873.

(492) R. v. Willemoes Suhm. " Preliminary note on the development of some pelagic Decapoda." Proc. of Royal Society, 1876.

Stomatopoda.

(493) W. K. Brooks. " On the larval stages of Squilla empusa." Chesapeake Zoological Laboratory, Scientific results of the Session of 1878. Baltimore, 1879 (494) C. Claus. "Die Metamorphose der Squilliden." Abhand. der kbnigl. Gesell. der Wiss. zu Gbttingen, 1871.

(495) Fr. Muller. " Bruchstuck a. der Entwicklungsgeschichte d. Maulfusser I. und II." Archiv f. Naturgeschichte, Vol. xxvin., 1862, and Vol. xxix., 1863.

Cumacea.

(496) A. Dohrn. " Ueber den Bau u. Entwicklung d. Cumaceen." Jenaische Zeitschrift, Vol. v., 1870.

Isopoda.

(497) Ed. van Beneden. " Recherches sur 1'Embryogenie des Crustaces. I. Asellus aquaticus." Bull, de FAcad. roy Belgique, 2me serie, Tom. xxvni., No. 7, 1869.

(498) N. Bobretzky. " Zur Embryologie des Oniscus murarius." Zeit. fur wiss. Zool., Bd. xxiv., 1874.

(499) J. F. Bullar. "On the development of the parasitic Isopoda." Phil. Trans., Part II., 1878.

(500) A. Dohrn. " Die embryonale Entwicklung des Asellus aquaticus." Zeit. f. wiss. Zool., Vol. xvn., 1867.

(501) H. Rathke. Untersuchungen iiber die Bildung tmd Entwicklung der Wasser-Assel. Leipzig, 1832.

(502) H. Rathke. Zur Morphologic. Reisebemerkungen aus Taurien. Riga u. Leipzig, 1837. (Bopyrus, Idothea, Ligia, lanira.)

342


532 BIBLIOGRAPHY.


A mphipoda.

(503) Ed. van Beneden and E. Bessels. "M&noire sur la formation du blastoderme chez les Amphipodes, les Lerneens et les Cope"podes." Classe des Sciences deTAcad. roy. de Belgique, Vol. xxxiv., 1868.

(504) De la Valletta St George. " Studien iiber die Entwicklung der Amphipoden." Abhand. d. naturfor. Gesell. zu Halle, Bd. v., 1860.

Copepoda.

(505) E. van Beneden and E. Bessels. " Me*moire sur la formation du blastoderme chez les Amphipodes, les Lerndens et Copepodes." Classe des Sciences de FAcad. roy. de Belgique, Vol. xxxiv., 1868.

(506) E. van Beneden. " Recherches sur 1'Embryogenie des Crustaces iv. Anchorella, Lerneopoda, Branchiella, Hessia." Bull, de FAcad. roy. de Belgique, 2me serie, T. xxix., 1870.

(507) C. Claus. Zur Anatomie u. Entwicklungsgeschichte d. Copepoden.

(508) C. Claus. " Untersuchungen Uber die Organisation u. Verwandschaft d. Copepoden." Wiirzburger naturwiss. Zeitschrift, Bd. III., 1862.

(509) C. Claus. " Ueber den Bau u. d. Entwicklung von Achtheres percarum." Zeit.f. wiss. Zool., Bd. XL, 1862.

(510) C. Claus. Die freilebenden Copepoden mit besonderer Berucksichtigung der Fauna Deutschlands, des Nordsee u. des Mittelmeeres. Leipzig, 1863.

(511) C. Claus. " Ueber d. Entwicklung, Organisation u. systematische Stellung d. Argulidse." Zeit.f. wiss. Zool., Bd. xxv., 1875.

(512) P. P. C. Hoek. " Zur Entwicklungsgeschichte d. Entomostracen." Niederldndisches Archiv, Vol. IV., 1877.

(513) N o r d m a n n. Mikrographische Beitrdge zur Naturgeschichte der ivirbellosen l^hiere. Zweites Heft. 1832.

(514) Salensky. " Sphseronella Leuckartii." Archivf. Naturgeschichte, 1868.

(515) F. Vejdovsky. "Untersuchungen Ub. d. Anat. u. Metamorph. v. Tracheliastes polycolpus." Zeit.f. wiss. Zool., Vol. xxix., 1877.

Cirripedia.

(516) C. Spence Bate. "On the development of the Cirripedia." Annals and Mag. of Natur. History. Second Series, Vin., 1851.

(517) E. van Beneden. " DeVeloppement des Sacculines." Bull, de I" Acad. roy. de Belg., 1870.

(518) C. Claus. Die Cypris-dhnliche Larve der Cifripedien. Marburg, 1869.

(519) Ch. Darwin. A monograph of the sub-class Cirripedia, i Vols., Ray Society, 18514.

(520) A. Dohrn. ' Untersuchungen iiber Bau u. Entwicklung d. Arthropoden ix. Eine neue Naupliusform (Archizoea gigas)." Zeit. f. wiss. Zool., Bd. xx., 1870.

(521) P. P. C. Hoek. "Zur Entwicklungsgeschichte der Entomostraken i. Kinbryologie von Balanus." Niederldndisches Archiv fur Zoologie, Vol. III., 1876 7.

(522) R. Kossmann. "Suctoria u. Lepadidoc." Arbeiten a. d. zool.-zoot. Instituted. Univer. Wiirz., Vol. I., 1873.


CRUSTACEA. 533


(523) Aug. Krohn. " Beobachtungen iiber die Entwicklung der Cirripedien." Wiegmanris Archiv fur Naturgesch., xxvi., 1860.

(524) E. Metschnikoff. Sitzungsberichte d. Versammlung deutscher Naturforscher zu Hannover, 1865. (Balanus balanoides.)

(525) Fritz Muller. "Die Rhizocephalen." Archiv f. Naturgeschichte, 1862-3.

(526) F. C. Noll. " Kochlorine hamata, ein bohrendes Cirriped." Zeit.f. wiss. Zool., Bd. xxv., 1875.

(527) A. Pagenstecher. " Beitrage zur Anatomic und Entwicklungsgeschichte von Lepas pectinata." Zeit.f. wiss. ZooL, Vol. xni., 1863.

(528) J. V. Thompson. Zoological Researches and Illustrations, Vol. I., Part I. Memoir IV. On the Cirripedes or Barnacles. 8vo. Cork, 1830.

(529) J. V. Thompson. " Discovery of the Metamorphosis in the second type of the Cirripedes, viz. the Lepades completing the natural history of these singular animals, and confirming their affinity with the Crustacea." Phil. Trans. 1835. Part n.

(530) R. von Willemoes Suhm. "On the development of Lepas fascicularis." Phil. Trans., Vol. 166, 1876.

Ostracoda.

(531) C. Glaus. " Zur naheren Kenntniss der Jugendformen von Cypris ovum." Zeit.f. wiss. ZooL, Bd. xv., 1865.

(532) C. Glaus. "Beitrage zur Kenntniss d. Ostracoden. Entwicklungsgeschichte von Cypris ovum." Schriften d. Gesell. zur Befdrderung d. gesamm. Naturwiss. zu Marburg, Vol. IX., 1868.


CHAPTER XIX. PCECILOPODA, PYCNOGONIDA, TARDIGRADA, AND LINGUATULIDA; AND COMPARATIVE SUMMARY OF ARTHROPODAN DEVELOPMENT

THE groups dealt with in the present Chapter undoubtedly belong to the Arthropoda. They are not closely related, and in the case of each group it is still uncertain with which of the main phyla they should be united. It is possible that they may all be offshoots from the Arachnidan phylum.

PCECILOPODA.

The development of Limulus has been studied by Dohrn (No. 533) and Packard (No. 534). The ova are laid in the sand near the spring-tide marks. They are enveloped in a thick chorion formed of several layers ; and (during the later stages of development at any rate) there is a membrane within the chorion which exhibits clear indications of cell outlines 1 .

There is a centrolecithal segmentation, which ends in the formation of a blastoderm enclosing a central yolk mass. A ventral plate is then formed, which is thicker in the region where the abdomen is eventually developed. Six segments soon become faintly indicated in the cephalothoracic region, the ends of which grow out into prominent appendages (fig. 245 A) ; of these there are six pairs, which increase in size from before backwards. A stomodaeum (m) is by this time established and is placed well in front of the foremost pair of appendages'*-.

In the course of the next few days the two first appendages of the abdominal region become formed (vide fig. 245 C shewing those abdominal appendages at a later stage), and have a very different shape and direction to those of the cephalothorax. The appendages of the latter become

1 The nature of the inner membrane is obscure. It is believed by Packard to be moulted after the formation of the limbs, and to be equivalent to the amnion of Insects, while by Dohrn it is regarded as a product of the follicle cells.

2 Dohrn finds at first only five appendages, but thinks that the sixth (the anterior one) may have been present but invisible.


PCECILOPODA.


535


flexed in the middle in such a way that their ends become directed towards the median line (fig. 245 B). The body of the embryo (fig. 245 B) is now distinctly divided into two regions the cephalothoracic in front, and the abdominal behind, both divided into segments.



FIG. 245. THREE STAGES IN THE DEVELOPMENT OF LIMULUS POLYPHEMUS. (Somewhat modified from Packard.)

A. Embryo in which the thoracic limbs and mouth have become developed on the ventral plate. The outer line represents what Packard believes to be the amnion.

B. Later embryo from the ventral surface.

C. Later embryo, just before the splitting of the chorion from the side. The full number of segments of the abdomen, and three abdominal appendages, have become established ; m. mouth ; I IX. appendages.

Round the edge of the ventral plate there is a distinct ridge the rudiment of the cephalothoracic shield.

With the further growth of the embryo the chorion becomes split and cast off, the embryo being left enclosed within the inner membrane. The embryo has a decided ventral flexure, and the abdominal region grows greatly and forms a kind of cap at the hinder end, while its vaulted dorsal side becomes divided into segments (fig. 245 C). Of these there are according to Dohrn seven, but according to Packard nine, of which the last forms the rudiment of the caudal spine.

In the thoracic region the nervous system is by this stage formed as a ganglionated cord (Dohrn), with no resemblance to the peculiar cesophageal ring of the adult. The mouth is stated by Dohrn to lie between the second pair of limbs, so that, if the descriptions we have are correct, it must have by this stage changed its position with reference to the appendages. Between the thorax and abdomen two papillae have arisen which form the


536


PCEC1LOPODA.


so-called lower lip of the adult, but from their position and late development they can hardly be regarded as segmental appendages. In the course of further changes all the parts become more distinct, while the membrane in which the larva is placed becomes enormously distended (fig. 246 A). The rudiments of the compound eyes are formed on the third (Packard) or fourth (Dohrn) segment of the cephalothorax, and the simple eyes near the median line in front. The rudiments of the inner process of the chelae of the cephalothoracic appendages arise as buds. The abdominal appendages become more plate-like, and the rudiments of a third pair appear behind the two already present. The heart appears on the dorsal surface.

An ecdysis now takes place, and in the stage following the limbs have approached far more closely to their adult state (fig. 246 A). The cephalothoracic appendages become fully jointed ; the two anterior abdominal appendages (vn.) have approached, and begin to resemble the oper


ce.



VIII


FlO. 246. TWO STAGES IN THE DEVELOPMENT OF LlMULUS POLYPHEMUS.

(After Dohrn.)

A. An advanced embryo enveloped in the distended inner membrane shortly before hatching ; from the ventral side.

B. A later embryo at the Trilobite stage, from the dorsal side. I., vii., VIII. First, seventh, and eight appendages.

cs. caudal spine ; se. simple eye ; ce. compound eye.

culum of the adult, and on the second pair is formed a small inner ramus. The segmentation of the now vaulted cephalothorax becomes less obvious, though still indicated by the arrangement of the yolk masses which form the future hepatic diverticula.

Shortly after this stage the embryo is hatched, and at about the time of hatching acquires a form (fig. 246 B) in which it bears, as pointed out by Dohrn and Packard, the most striking resemblance to a Trilobite.

Viewed from the dorsal surface (fig. 246 B) it is divided into two distinct regions, the cephalothoracic in front and the abdominal behind. The cephalothoracic has become much flatter and wider, has lost all trace of its previous segmentation, and has become distinctly trilobed. The


PCECILOPODA. 537


central lobe forms a well-marked keel, and at the line of insertion of the rim-like edge of the lateral lobes are placed the two pairs of eyes (se and ce). The abdominal region is also distinctly trilobed and divided into nine segments ; the last, which is merely formed of a median process, being the rudiment of the caudal spine. The edges of the second to the seventh are armed with a spine. The changes in the appendages are not very considerable. The anterior pair nearly meet in the middle line in front or the mouth ; and the latter structure is completely covered by an upper lip. Each abdominal appendage of the second pair is provided with four gill-lamellas, attached close to its base.

Three weeks after hatching an ecdysis takes place, and the larva passes from a trilobite into a limuloid form. The segmentation of the abdomen has become much less obvious, and this part of the embryo closely resembles its permanent form. The caudal spine is longer, but is still relatively short. A fourth pair of abdominal appendages is established, and the first pair have partially coalesced, while the second and third pairs have become jointed, their outer ramus containing four and their inner three joints. Additional gill-lamellae attached to the two basal joints of the second and third abdominal appendages have appeared.

The further changes are not of great importance. They are effected in a series of successive moults. The young larvae swim actively at the surface.

Our, in many respects, imperfect knowledge of the development of Limulus is not sufficient to shew whether it is more closely related to the Crustacea or to the Arachnida, or is an independent phylum.

The somewhat Crustacean character of biramous abdominal feet, etc. is not to be denied, but at the same time the characters of the embryo appear to me to be decidedly more arachnidan than crustacean. The embryo, when the appendages are first formed, has a decidedly arachnidan facies. It will be remembered that when the limbs are first formed they are all post-oral. They resemble in this respect the limbs of the Arachnida, and it seems to be probable that the anterior pair is equivalent to the cheliceras of Arachnida, which, as shewn in a previous section, are really post-oral appendages in no way homologous with antennae 1 .

The six thoracic appendages may thus be compared with the six Arachnidan appendages; which they resemble in their relation to the mouth, their basal cutting blades, etc.

The existence of abdominal appendages behind the six cephalothoracic does not militate against the Arachnidan affinities of Limulus, because in the Arachnida rudimentary abdominal appendages are always present in the embryo. The character of the abdominal appendages is probably

1 Dohrn believes that he has succeeded in shewing that the first pair of appendages of Limulus is innervated in the embryo from the supra-cesophageal ganglia. His observations do not appear to me conclusive, and, arguing from what we know of the development of the Arachnida, the innervation of these appendages in the adult can be of no morphological importance.


538 PYCNOGONIDA.


secondarily adapted to an aquatic respiration, since it is likely (for the reasons already mentioned in connection with the Tracheata) that if Limulus has any affinities with the stock of the Tracheata it is descended from airbreathing forms, and has acquired its aquatic mode of respiration. The anastomosis of the two halves of the generative glands is an Arachnidan character, and the position of the generative openings in Limulus is more like that in the Scorpion than in Crustacea.

A fuller study of the development would be very likely to throw further light on the affinities of Limulus, and if Packard's view about the nature of the inner egg membrane were to be confirmed, strong evidence would thereby be produced in favour of the Arachnidan affinities.

(533) A. Dohrn. "Untersuch. Ub. Bau u. Entwick. d. Arthropoden (Limulus polyphemus)." Jenaische Zeitschrift, Vol. vi., 1871.

(534) A. S. Packard. "The development of Limulus polyphemus." Mem. Boston Soc. Nat. History, Vol. II., 1872.

PYCNOGONIDA.

The embryos, during the first phases of their development, are always carried by the male in sacks which are attached to a pair of appendages (the third) specially formed for this purpose. The segmentation of the ovum is complete, and there is in most forms developed within the eggshell a larva with three pairs of two-jointed appendages, and a rostrum placed between the front pair.

It will be convenient to take Achelia kevis, studied by Dohrn (No. 536), as type.

The larva of Achelia when hatched is provided with the typical three pairs of appendages. The foremost of them is chelate, and the two following pairs are each provided with a claw. Of the three pairs of larvalappendages Dohrn states that he has satisfied himself that the anterior is innervated by the supra-cesophageal ganglion, and the two posterior by separate nerves coming from two imperfectly united ventral ganglia. The larva is provided with a median eye formed of two coalesced pigment spots, and with a simple stomach.

The gradual conversion of the larva into the adult takes place by the elongation of the posterior end of the body into a papilla, and the formation there, at a later period, of the anus ; while at the two sides of the anal papilla rudiments of a fresh pair of appendages the first pair of ambulatory limbs of the adult make their appearance. The three remaining pairs of limbs become formed successively as lateral outgrowths, and their development is accomplished in a number of successive ecdyses. As they are formed caeca from the stomach become prolonged into them. For each of them there appears a special ganglion. While the above changes are taking place the three pairs of larval appendages undergo considerable reduction. The anterior pair singly becomes smaller, the second loses its claw, and the third becomes reduced to a mere stump. In the adult the


PENTASTOMIDA. 539


second pair of appendages becomes enlarged again and forms the so-called palpi, while the third pair develops in the male into the egg-carrying appendages, but is aborted in the female. The first pair form appendages lying parallel to the rostrum, which are sometimes called pedipalpi and sometimes antennae.

The anal papilla is a rudimentary abdomen, and, as Dohrn has shewn, contains rudiments of two pairs of ganglia.

The larvae of Phoxichilidium are parasitic in various Hydrozoa (Hydractinia, etc.). After hatching they crawl into the Hydractinia stock. They are at first provided with the three normal pairs of larval appendages. The two hinder of these are soon thrown off, and the posterior part of the trunk, with the four ambulatory appendages belonging to it, becomes gradually developed in a series of moults. The legs, with the exception of the hindermost pair, are fully formed at the first ecdysis after the larva has become free. In the genus Pallene the metamorphosis is abbreviated, and the' young are hatched with the full complement of appendages.

The position of the Pycnogonida is not as yet satisfactorily settled. The six-legged larva has none of the characteristic features of the Nauplius, except the possession of the same number of appendages.

The number of appendages (7) of the Pycnogonida does not coincide with that of the Arachnida. On the other hand, the presence of chelate appendages innervated in the adult by the supra-cesophageal ganglia rather points to a common phylum for the Pycnogonida and Arachnida ; though as shewn above (p. 455) all the appendages in the embryo of true Arachnida are innervated by post-oral ganglia. The innervation of these appendages in . the larvae of Pycnogonida requires further investigation. Against such a relationship the extra pair of appendages in the Pycnogonida is no argument, since the embryos of most Arachnida are provided with four such extra pairs. The two groups must no doubt have diverged very early.

BIBLIOGRAPHY.

(535) G. Cavanna. " Studie e ricerche sui Picnogonidi." Pubblicazioni del R. Institute di Studi stiperiori in Firenze, 1877.

(536) An. Dohrn. " Ueber Entwickhuig u. Baud. Pycnogoniden." Jenaische Zeitschrift, Vol. v. 1870, and " Neue Untersuchungen lib. Pycnogoniden." Mitthdl. a. d. zoologischen Station zu Neafel, Bd. I. 1878.

(537) G. Hodge. " Observations on a species of Pycnogon, etc." Annal. and Mag. of Nat. Hist. Vol. ix. 1862.

(538) C. Semper. " Ueber Pycnogoniden u. ihre in Hydroiden schmarotzenden Larvenformen." Arbeiten a. d. zool.-zoot. Instit. Wiirzburg, Vol. I. 1874.

PENTASTOMIDA.

The development and metamorphosis of Pentastomum taenoides have been thoroughly worked out by Leuckart (No. 540) and will serve as type for the group.


540 PENTASTOMIDA.


In the sexual state it inhabits the nasal cavities of the dog. The early embryonic development takes place as the ovum gradually passes down the uterus. The segmentation appears to be complete ; and gives rise to an oval mass in which the separate cells can hardly be distinguished. This gradually differentiates itself into a characteristic embryo, divided into a tail and trunk. The tail is applied to the ventral surface of the trunk, and on the latter two pairs of stump-like unsegmented appendages arise, each provided with a pair of claws. At the anterior extremity of the body is formed the mouth, with a ventral spine and lateral hook, which are perhaps degenerated jaws. The spine functions as a boring apparatus, and an apparatus with a similar function is formed at the end of the tail. A larval cuticle now appears, which soon becomes detached from the embryo, except on the dorsal surface, where it remains firmly united to a peculiar papilla. This papilla becomes eventually divided into two parts, one of which remains attached to the cuticle, while the part connected with the embryo forms a raised cross placed in a cup- shaped groove. The whole structure has been compared, on insufficient grounds, to the dorsal organ of the Crustacea.

The eggs, containing the embryo in the condition above described, are eventually carried out with the nasal slime, and, if transported thence into the alimentary cavity of a rabbit or hare, the embryos become hatched by the action of the gastric juice. From the alimentary tract of their new host they make their way into the lungs or liver. They here become enveloped in a cyst, in the interior of which they undergo a very remarkable metamorphosis. They are, however, so minute and delicate that Leuckart was unable to elucidate their structure till eight weeks after they had been swallowed. At this period they are irregularly-shaped organisms, with a most distant resemblance to the earlier embryos. They are without their previous appendages, but the alimentary tract is now distinctly differentiated. The remains of two cuticles in the cyst seem to shew that the above changes are effected in two ecdyses.

In the course of a series of ecdyses the various organs of the larval form known as Pentastomum denticulatum continue to become differentiated. After the first (= third) ecdysis the cesophageal nerve-ring and sexually undifferentiated generative organs are developed. At the fourth (=sixth) ecdysis the two pairs of hooks of the adult are formed in pockets which appeared at a somewhat earlier stage ; and the body acquires an annulated character. At a somewhat earlier period rudiments of the external generative organs indicate the sex of the larva.

After a number of further ecdyses, which are completed in about six months after the introduction of the embryos into the intermediate host, the larva attains its full development, and acquires a form in which it has long been known as Pentastomum denticulatum. It now leaves its cyst and begins to move about. It is in a state fit to be introduced into its final host ; but if it be not so introduced it may become encysted afresh.

If the part of a rabbit or hare infected by a Pentastomum denticulatum be eaten by a dog or wolf, the parasite passes into the nasal cavity of the


TARDIGRADA. 541


latter, and after further changes of cuticle becomes a fully-developed sexual Pentastomum taenioides, which does not differ to any very marked extent from P. denticulatum.

In their general characters the larval migrations of Pentastomum are similar to those of the Cestodes.

The internal anatomy of the adult Pentastomum, as well as the characters of the larva with two pairs of clawed appendages, are perhaps sufficient to warrant us in placing it with the Arthropoda, though it would be difficult to shew that it ought not to be placed with such a form as Myzostomum (vide p. 369). There do not appear to be any sufficient grounds to justify its being placed with the Mites amongst the Arachnida. If indeed the rings of the body of the Pentastomida are to be taken as implying a true segmentation, it is clear that the Pentastomida cannot be associated with the Mites.

BIBLIOGRAPHY.

(539) P. J. van Beneden. " Recherches s. 1'organisation et le developpement d. Linguatules." Ann. d. Sden. Nat., 3 Ser., Vol. XI.

(540) R. Leuckart. " Bau u. Entwicklungsgeschichte d. Pentastomen." Leipzig and Heidelberg. 1860.

TARDIGRADA.

Very little is known with reference to the development of the Tardigrada. A complete and regular segmentation (von Siebold, Kaufmann, No. 541) is followed by the appearance of a groove on the ventral side indicating a ventral flexure. At about the time of the appearance of the groove the cells become divided into an epiblastic investing layer and a central hypoblastic mass.

The armature of the pharynx is formed very early at the anterior extremity, and the limbs arise in succession from before backwards.

The above imperfect details throw no light on the systematic position of this group.

Tardigrada.

(541) J. Kaufmann. " Ueber die Entwicklung u. systematische Stellung d. Tardigraden." Zeit.f. wiss, ZooL, Bd. HI. 1851.

Summary of Arthropodan Development. The numerous characters common to the whole of the Arthropoda led naturalists to unite them in a common phylum, but the later researches on the genealogy of the Tracheata and Crustacea tend to throw doubts on this conclusion, while there is not as yet sufficient evidence to assign with certainty a definite position in either of these classes to the smaller groups described in the present chapter. There seems to be but little


542 SUMMARY.


doubt that the Tracheata are descended from a terrestrial Annelidan type related to Peripatus. The affinities of Peripatus to the Tracheata are, as pointed out in a previous chapter (p. 386), very clear, while at the same time it is not possible to regard Peripatus simply as a degraded Tracheate, owing to the fact that it is provided with such distinctly Annelidan organs as nephridia, and that its geographical distribution shews it to be a very ancient form.

The Crustacea on the other hand are clearly descended from a Phyllopod-like ancestor, which can be in no way related to Peripatus.

The somewhat unexpected conclusion that the Arthropoda have a double phylum is on the whole borne out by the anatomy of the two groups. Without attempting to prove this in detail, it may be pointed out that the Crustacean appendages are typically biramous, while those of the Tracheata are never at any stage of development biramous 1 ; and the similarity between the appendages of some of the higher Crustacea and those of many Tracheata is an adaptive one, and could in no case be used as an argument for the affinity of the two groups.

The similarity of many organs is to be explained by both groups being descendants of Annelidan ancestors. The similarity of the compound eye in the two groups cannot however be explained in this way, and is one of the greatest difficulties of the above view. It is moreover remarkable that the eye of Peripatus 2 is formed on a different type to either the single or compound eyes of most Arthropoda.

The conclusion that the Crustacea and Tracheata belong to two distinct phyla is confirmed by a consideration of their development. They have no doubt in common a centrolecithal segmentation, but, as already insisted on, the segmentation is no safe guide to the affinities.

In the Tracheata the archenteron is never, so far as we know, formed by an invagination 3 , while in Crustacea the

1 The biflagellate antennae of Pauropus amongst the Myriapocls can hardly be considered as constituting an exception to this rule.

3 I hope to shew this in a paper I am preparing on the anatomy of Peripatus.

8 Stecker's description of an invagination in the Chilognatha cannot be accepted without further confirmation ; -vide p. 388.


SUMMARY. 543


evidence is in favour of such an invagination being the usual, and, without doubt, the primitive, mode of origin.

The mesoblast in the Tracheata is formed in connection with a median thickening of the ventral plate. The unpaired plate of mesoblast so formed becomes divided into two bands, one on each side of the middle line.

In both Spiders and Myriopods, and probably Insects, the two plates of mesoblast are subsequently divided into somites, the lumen of which is continued into the limbs.

In Crustacea the mesoblast usually originates from the walls of the invagination, which gives rise to the mesenteron.

It does not become divided into two distinct bands, but forms a layer of scattered cells between the epiblast and hypoblast, and does not usually break up into somites ; and though somites are stated in some cases to be found they do not resemble those in the Tracheata.

The proctodaeum is usually formed in Crustacea before and rarely later 1 than the stomodaeum. The reverse is true for the Tracheata. In Crustacea the proctodseum and stomodaeum, especially the former, are very long, and usually give rise to the greater part of the alimentary tract, while the mesenteron is usually short.

In the Tracheata the mesenteron is always considerable, and the proctodaeum is always short. The derivation of the Malpighian bodies from the proctodaeum is common to most Tracheata. Such diverticula of the proctodaeum are not found in Crustacea.

1 This is stated to be the case in Moina (Grobben).


CHAPTER XX.


ECHINODERMATA 1 .

THE development of the Echinodermata naturally falls into two sections:

(i) The development of the germinal layers and of the systems of organs; (2) the development of the larval appendages and the metamorphosis.

The Development of the Germinal Layers and of tJie Systems

of Organs.

The development of the systems of organs presents no very important variations within the limits of the group.

Holothuroidea. The Holothurians have been most fully studied (Selenka, No. 563), and may be conveniently taken as type.

The segmentation is nearly regular, though towards its close, and in some instances still earlier, a difference becomes apparent between the upper and the lower poles.

At the close of segmentation (fig. 247 A) the egg has a nearly spherical form, and is constituted of a single layer of columnar cells enclosing a small segmentation cavity. The lower pole is slightly thickened, and the egg rotates by means of fine cilia.

An invagination now makes its appearance at the lower pole (fig. 247 B), and simultaneously there become budded off from tJie cells undergoing the invagination amoeboid cells, which

1 The following classification of the Echinodermata is employed in this chapter.

I. Holothuroidea. IV. Echinoidea.

II. Asteroidea. V. Crinoidea.

III. Ophiuroidea.


ECHINODERMATA. 545


eventually form the muscular system and the connective tissue. These cells very probably have a bilaterally symmetrical origin. This stage represents the gastrula stage which is common to all Echinoderms. The invaginated sack is the archenteron. As it grows larger one side of the embryo becomes flattened, and the other more convex. On the flattened side a fresh invagination



FIG. 247. TWO STAGES IN THE DEVELOPMENT OF HOLOTHURIA TUBULOSA

VIEWED IN OPTICAL SECTION. (After Selenka.) A. Blastosphere stage at the close of segmentation. B. Gastrula stage. mr. micropyle ; //. chorion; s.c. segmentation cavity; bl. blastoderm; ep. epiblast; hy. hypoblast; ms. amoeboid cells derived from hypoblast ; a.e. archenteron.

arises, the opening of which forms the permanent mouth, the opening of the first invagination remaining as the permanent anus (fig. 248 A).

These changes give us the means of attaching definite names to the various parts of the embryo. It deserves to be noted in the first place that the embryo has assumed a distinctly bilateral form. There is present a more or less concave surface extending from the mouth to near the anus, which will be spoken of as the ventral surface. The anus is situated at the posterior extremity. The convex surface opposite the ventral surface forms the dorsal surface, which terminates anteriorly in a rounded prse-oral prominence.

It will be noticed in fig. 248 A that in addition to the primitive anal invagination there is present a vesicle (?/.). This vesicle is directly formed by a constriction of the primitive B. II. 35


54 6


HOLOTHUROIDEA.


archenteron (fig. 249 Vpv.), and is called by Selenka the vasoperitoneal vesicle. It gives origin to the epithelioid lining of the body cavity and water-vascular system of the adult 1 . In the parts now developed we have the rudiments of all the adult organs. The mouth and anal involutions (after the separation of the vaso-peritoneal vesicle) meet and unite, a constriction indicating their point of junction (fig. 248 B). Eventually the former gives



FIG. 248. THREE STAGES IN THE DEVELOPMENT OF HOLOTHURIA TUBULOSA

VIEWED FROM THE SIDE IN OPTICAL SECTION. (After Selenka.) tn. mouth; oe. oesophagus; st. stomach; i. intestine; a. anus; I.e. longitudinal ciliated band; v.p. vaso-peritoneal vesicle; p.v. peritoneal vesicle; p.r. right peritoneal vesicle ; //. left peritoneal vesicle ; w.v. water- vascular vesicle ; p. dorsal pore of water- vascular system ; ms. muscle cells.

rise to the mouth and cesophagus, and the latter to the remainder of the alimentary canal 2 .

The vaso-peritoneal vesicle undergoes a series of remarkable changes. After its separation from the archenteron it takes up a position on the left side of this, elongates in an anteroposterior direction, and from about its middle sends a narrow diverticulum towards the dorsal surface of the body, where an

1 The origin of the vaso-peritoneal vesicle is not quite the same in all the species. In Holothuria tubulosa it is separated from the csecal end of the archenteron; the remainder of which then grows towards the oral invagination. In Cucumaria the archenteron forks (fig. 249) ; and one fork forms the vaso-peritoneal vesicle, and the other the major part of the mesenteron.

2 There appears to be some uncertainty as to how much of the larval cesophagus is derived from the stomodaeal invagination.


ECHINODERMATA.


547


opening to the exterior becomes formed (fig. 248 B, /.). The diverticulum becomes the madreporic canal, and the opening the dorsal pore.

The vaso-peritoneal vesicle next divides into two, an anterior vesicle (fig. 248 B, w.v.), from which is derived the epithelium of the water-vascular system, and a posterior (fig. 248 B, /.?;.), which gives rise to the epithelioid lining of the body cavity. The anterior vesicle (fig. 248 C, w.v.) becomes fivelobed, takes a horseshoe-shaped form, and grows round the oesophagus (fig. 256, w.v.r). The five lobes form the rudiments of the water-vascular prolongations into the tentacles. The remaining parts of the water-vascular system are also developed as outgrowths of the original vesicle. Five of these, alternating with the original diverticula, form the five ambulacral canals, from which diverticula are produced into the ambulacral feet ; a sixth gives rise to the Polian vesicle. The remaining parts of the original vesicle form the water-vascular ring.

We must suppose that eventually the madreporic canal loses its connection with the exterior so as to hang loosely in the interior, though the steps of this process do not appear to have been made out.

The original hinder peritoneal vesicle grows rapidly, and divides into two (fig. 248 C, pi. and pr.}, which encircle the two sides of the alimentary canal, and meet above and below it. The outer wall of each of them attaches itself to the skin, and the inner one to the alimentary canal and watervascular system ; in both cases the walls remain separated from the adjacent parts by a layer of the amoeboid cells already spoken of. The cavity of the peritoneal vesicles becomes the permanent body cavity. Where the walls of



-ME


FIG. 249. LONGITUDINAL SECTION

THROUGH AN EMBRYO OF CUCUMARIA DOLIOLUM AT THE END OF THE FOURTH DAY.

Vpv. vaso-peritoneal vesicle; ME. mesenteron; Blp., Ptd. blastopore, proctodaeum.

352


548 HOLOTHUROIDEA.


the two vesicles meet on the dorsal side, a mesentery, suspending the alimentary canal and dividing the body cavity longitudinally, is often formed. In other parts the partition walls between the two sacks appear to be absorbed.

The amoeboid cells, which were derived from the invaginated cells, arrange themselves as a layer round all the organs (fig. 249). Some of them remain amoeboid, attach themselves to the skin, and form part of the cutis; and in these cells the calcareous spicula of the larva and adult are formed. Others form the musculature of the larval alimentary tract, while the remainder give rise to the musculature and connective tissue of the adult.

The development of the vascular system is not known, but the discovery of Kowalevsky, confirmed by Selenka, that from the walls of the watervascular system corpuscles are developed, identical with those in the bloodvessels, indicates that it probably develops in connection with the watervascular system. The observations of Hoffmann and Perrier on the communication of the two systems in the Echinoidea point to the same conclusion. Though nothing very definite is known with reference to the development of the nervous system, Metschnikoff suggests that it develops in connection with the thickened bands of epiblast which are formed by a metamorphosis of the ciliated bands of the embryo, and accompany the five radial tubes (vide p. 555). In any case its condition in the adult leaves no doubt of its being a derivative of the epiblast.

From the above description the following general conclusions may be drawn :

(1) The blastosphere stage is followed by a gastrula stage.

(2) The gastrula opening forms the permanent anus, and the mouth is formed by a fresh invagination.

(3) The mesoblast arises entirely from the invaginated cells, but in two ways :

(a) As scattered amoeboid cells, which give origin to the muscles and connective tissue (including the cutis) of the body wall and alimentary tract.

(&) As a portion separated off from the archenteron, which gives rise both to the epithelioid lining of the body cavity, and of the water-vascular system.

(4) The oesophagus is derived from an invagination of the epiblast, and the remainder of the alimentary canal from the archenteron.


ECHINODERMATA. 549


(5) The embryonic systems of organs pass directly into those of the adult.

The development of Synapta diverges, as might be expected, to a very small extent from that of Holothuria.

Asteroidea. In Asterias the early stages of development conform to our type. There arise, however, two bilaterally symmetrical vaso-peritoneal diverticula from the archenteron. These diverticula give rise both to the lining of the body cavity and water-vascular system. With reference to the exact changes they undergo there is, however, some difference of opinion. Agassiz (543) maintains that both vesicles are concerned in the formation of the water-vascular system, while Metschnikoff (560) holds that the watervascular system is entirely derived from the anterior part of the larger left vesicle, while the right and remainder of the left vesicle form the body cavity. MetschnikofFs statements appear to be the most probable. The anterior part of the left vesicle, after separating from the posterior, grows into a five-lobed rosette (fig. 260, /), and a madreporic canal (h] with a dorsal pore opening to the exterior. The rosette appears not to grow round the oesophagus, as in the cases hitherto described. But the latter is stated to disappear, and a new oesophagus to be formed, which pierces the rosette, and places the old mouth in communication with the stomach. Except where the anus is absent in the adult, the larval anus probably persists.

Ophiuroidea. The early development of the Ophiuroidea is not so fully known as that of other types. Most species have a free-swimming larva, but some (Amphiura) are viviparous.

The early stages of the free-swimming larvae have not been described, but I have myself observed in the case of Ophiothrix fragilis that the segmentation is uniform, and is followed by the normal invagination. The opening of this no doubt remains as the larval anus, and there are probably two outgrowths from this to form the vaso-peritoneal vesicles. Each of these divides into two parts, an anterior lying close to the oesophagus, and a posterior close to the stomach. The anterior on the right side aborts ; that on the left side becomes the water-vascular vesicle, early opens to the exterior, and eventually grows round the oesophagus, which, as in Holothurians, becomes the oesophagus of the adult. The posterior vesicles give rise to the lining of the body cavity, but are stated by Metschnikoff to be at first solid, and only subsequently to acquire a cavity the permanent body cavity. The anus naturally disappears, since it is absent in the adult. In the viviparous type the first stages are imperfectly known, but it appears that the blastopore vanishes before the appearance of the mouth. The development of the ^vaso-peritoneal bodies takes place as in the free-swimming larvae.

Echinoidea. In the Echinoidea (Agassiz, No. 542, Selenka, No. 564) there is a regular segmentation and the normal invagination (fig. 250 A). The amoeboid mesoblast cells arise as two laterally placed masses, and give rise to the usual parts. The archenteron grows forward and bends towards


550


CRINOIDEA.


the ventral side (fig. 250 B). It becomes (fig. 250 C) divided into three chambers, of which the two hindermost (d and c) form the stomach and intestine ; while the anterior forms the oesophagus, and gives rise to the



FIG. 250. THREE SIDE VIEWS OF EARLY STAGES IN THE DEVELOPMENT OF

STRONGYLOCENTRUS. (From Agassiz.)

a, anus (blastopore) ; d. stomach ; o. oesophagus ; c . rectum ; w. vaso-peritoneal vesicle ; v. ciliated ridge ; r. calcareous rod.

vaso-peritoneal vesicles. These latter appear as a pair of outgrowths (fig. 251), but become constricted off as a single two-horned vesicle, which subsequently divides into two. The left of these is eventually divided, as in Asteroids, into a peritoneal and water-vascular sack, while the right forms the right peritoneal sack. An oral invagination on the flattened ventral side meets the mesenteron after its separation from the vaso-peritoneal vesicle. The larval anus persists, as also does the larval mouth, but owing to the manner in which the water-vascular rosette is established the larval oesophagus appears to be absorbed, and to be replaced by a fresh oesophagus.

Crinoidea. Antedon, the only Crinoid so far studied (Gotte, No. 549), presents some not inconsiderable variations from the usual Echinoderm type. The blastopore is placed on the somewhat flattened side of the oval blastosphere, and not, as is usual, at the hinder end.

The blastopore completely closes, and is not converted into the permanent anus. The archenteron gives rise to the epithelioid lining of both body cavity and water-vascular system. These parts do not, however, appear as a single or paired outgrowth from the archenteron, but as three distinct outgrowths which are not formed contemporaneously. Two of them are first



FIG. -251. DORSO-VENTRAL VIEW OF AN EARLY LARVA OF STRONGYLOCENTRUS. (From Agassiz.)

a. anus ; d. stomach ; o. oesophagus ; w. vaso-peritoneal vesicle; r. calcareous rod.


ECHINODERMATA.


551


formed and become the future body cavity; but their lumens remain distinct. Jngmally appearing as lateral outgrowths, the right one assumes a dorsal position and sends a prolongation into the stalk (fig. 252 rp'\ and the left one assumes first a ventral, and then an oral position (fur 252 lp\

The third outgrowth of the archenteron gives rise to the water-vascular vesicle. It first grows round the region of the future oesophagus and so forms the water-vascular ring. The wall of the ring then grows towards the body wall so as to divide the oral (left) peritoneal vesicle into two distinct vesicles, an anterior and a posterior, shewn in fig. 253, lp' and lp. Before this division is completed, the water-vascular ring is produced in front into five pro


FIG. 252. LONGITUDINAL SECTION THROUGH AN ANTEDON LARVA. (From Carpenter: after Gotte.)


al. mesenteron ; -wv. water- vascular ring ; lp. left (oral) peritoneal vesicle; rp. right peritoneal vesicle ; rp'. continuation of right vesicle into the stalk ; st. stalk.


cessesthe future tentacles (fig. 252, wv) which project into the cavity of the oral vesicle (lp\ After the oral peritoneal space has become completely divided into two parts, the anterior dilates (fig. 253, //) greatly, and forms a large vestibule at the anterior end of the body. This vestibule (lp'} next acquires a communication with the mesenteron, shewn in fig. 253 at m. The anterior wall of this vestibule is finally broken through. By this rupture the mesenteron is placed in communication with the exterior by the opening at m, while at the same time the tentacles of the water-vascular ring (/) project freely to the exterior. Such is Gotte's account of the prge-oral body space, but, as he himself points out, it involves our believing that the lining of the diverticulum derived from the primitive alimentary vesicle becomes part of the external skin. This occurrence is so remarkable, that more evidence appears to me requisite before accepting it.

The formation of the anus occurs late. Its position appears to be the same as that of the blastopore, and is indicated by a papilla of the mesenteron attaching itself to the skin on the ventral side (fig. 253, an). It eventually becomes placed in an interradial space within the oral disc of the adult. The water-vascular ring has no direct communication with the exterior, but the place of the madreporic canal of other types appears to be taken in the larva by a single tube leading from the exterior into the body cavity, the external opening of which is placed on one of the oral plates (vide p. 571) in the next interradial space to the right of the anus, and a corresponding diverticulum of the water-vascular ring opening into the body cavity. The line of junction between the left and right peritoneal vesicles forms in the larva a ring-like mesentery dividing the oral from the aboral part of the body


552


CRINOIDEA.


cavity. In the adult 1 the oral section of the larval body cavity becomes the ventral part of the circumvisceral division of the body cavity, and the subtentacular canals of the arms and disc ; while the aboral section becomes the dorsal part of the circumvisceral division of the body cavity, the cceliac canals of the arms, and the cavity of the centro-dorsal piece. The primitive


,+wr



FIG. 253. LONGITUDINAL SECTION THROUGH THE CALYX OF AN ADVANCED PENTRACRINOID ANTEDON LARVA WITH CLOSED VESTIBULE.

(From Carpenter ; after Gotte.)

ae. epithelium of oral vestibule; ;//. mouth; al. mesenteron; an. rudiment of permanent anus; lp. posterior part of left (oral) peritoneal sack; lp' '. anterior part of left (oral) peritoneal sack; wr. water-vascular ring; /. tentacle; mt. mesentery; rp. right peritoneal sack; rp '. continuation of right peritoneal sack into the stalk; r. roof of tentacular vestibule.

distinction between the sections of the larval body cavity becomes to a large extent obliterated, while the axial and intervisceral sections of the bodycavity of the adult are late developments.

The more important points in the development indicated in the preceding pages are as follows :

(i) The blastosphere is usually elongated in the direction of the axis of invagination, but in Comatula it is elongated transversely to this axis.

1 Vide P. H. Carpenter, "On the genus Actinometra." Linnean Trans., and Series, Zoology, Vol. n., Part I., 1879.


ECHINODERMATA. 553


(2) The blastopore usually becomes the permanent anus, but it closes at the end of larval life (there being no anus in the adult) in Ophiuroids and some Asteroids, while in Comatula it closes very early, and a fresh anus is formed at the point where the blastopore was placed.

(3) The larval mouth always becomes the mouth of the adult.

(4) The archenteron always gives rise to outgrowths which form the peritoneal membrane and water-vascular systems. In Comatula there are three such outgrowths, two paired, which form the peritoneal vesicles, and one unpaired, which forms the water-vascular vesicle. In Asteroids and Ophiuroids there are two outgrowths. In Ophiuroids both of these are divided into a peritoneal and a water-vascular vesicle, but the right watervascular vesicle atrophies. In Asteroids only one water-vascular vesicle is formed, which is derived from the left peritoneal vesicle. In Echinoids and Holothuroids there is a single vaso-peritoneal vesicle.

(5) The water- vascular vesicle grows round the larval oesophagus in Holothuroids, Ophiuroids, and Comatula ; in these cases the larval oesophagus is carried on into the adult. In other forms the water-vascular vesicle forms a ring which does not enclose the cesophagus (Asteroids and Echinoids); in such cases a new oesophagus is formed, which perforates this ring.

Development of the larval appendages and metamorphosis.

Holothuroidea. The young larva of Synapta, to which J. Muller gave the name Auricularia (fig. 255), is in many respects the simplest form of Echinoderm larva. With a few exceptions the Auricularia type of larva is common to the Holothuria.

It is (fig. 254 A and fig. 255) bilaterally symmetrical, presenting a flattened ventral surface, and a convex dorsal one. The anus (an) is situated nearly at the hinder pole, and the mouth (m) about the middle of the ventral surface. In front of the mouth is a considerable process, the prae-oral lobe. Between the mouth and anus is a space, more or less concave according to the age of the embryo, interrupted by a ciliated


554


AURICULARIA.


A similar ciliated ridge is A E


ridge a little in front of the anus, present on the ventral surface of the prae-oral lobe immediately in front of the mouth. The anal and oral ridges are connected by two lateral ciliated bands, the whole forming a continuous band, which, since the mouth lies in the centre of it (fig. 255), may be regarded as a ring completely surrounding the body behind the mouth, or more naturally as a longitudinal ring.

The bilateral Auricularia is developed from a slightly elongated gastrula with an uniform covering of cilia. The gastrula becomes flattened on the oral side. At the same time the cilia become specially developed on the oral and anal ridges, and then on the remainder of the ciliated ring, while they are



FIG. 254. A. THE LARVA OF A HOLOTHUROID. B. THE LARVA OF AN ASTEROID.

//. mouth; st. stomach; a. anus; l.c>

primitive longitudinal ciliated band; pr.c. prae-oral ciliated band.



FIG. 155. DIAGRAMMATIC FIGURES REPRESENTING THE EVOLUTION OF AN AURICULARIA FROM THE SIMPLEST ECHINODERM LARVAL FORM. (Copied from MUller.)

The black line represents the ciliated ridge. The shaded part is the oral side of the ring, the clear part the aboral side.

/;;. mouth; an. anus.

simultaneously obliterated elsewhere ; and so a complete Auricularia is developed. The water-vascular ring in the fully-developed larva has already considerably advanced in the growth round the oesophagus (fig. 256 w.v.r).

Most Holothurian larvae, in their transformation from the bilateral Auricularia form to the radial form of the adult, pass through a stage in which the cilia form a number of transverse


ECHINODERMATA.


555



-2>.v


rings, usually five in number, surrounding the body. The stages in this metamorphosis are shewn in figs. 256, 257, and 258.

The primitive ciliated band, at a certain stage of the metamorphosis, breaks up into a number of separate portions (fig. 256), the whole of which are placed on the ventral surface. Four of these (fig. 257 A and B) arrange themselves in the form of an angular ring round the mouth, which at this period projects considerably. The remaining portions of the primitive band change their direction from a longitudinal one to a transverse (fig. 257 B), and eventually grow into complete rings (fig. 2570). Of these there are five. The middle one (257 B) is the first to develop, and is formed from the dorsal parts of the primitive ring. The two hinder rings develop next, and last of all the two anterior ones, one of which appears to be in front of the mouth (fig. 257 C).

The later development of the mouth, and of the ciliated ridge surrounding it, is involved in some obscurity. It appears from Metschnikoff (No. 560) that an invagination of the oesophagus takes place, carrying with it the ciliated ridge around the mouth. This ridge becomes eventually converted into the covering for the five tentacular outgrowths of the water- vascular ring (fig. 258), and possibly also forms the nervous system.

The opening of the cesophageal invagination is at first behind the foremost ciliated ring, but eventually comes to lie in front of it, and assumes a nearly terminal though slightly ventral position (fig. 258). No account has been given of the process by which this takes place, but the mouth is stated by Metschnikoff (though


FIG. 256. FULL-GROWN LARVA OF SYNAPTA. (After Metschnikoff.)

m. mouth ; st. stomach ; a. anus ; p.v. left division of perivisceral cavity, which is still connected with the watervascular system ; w.v.r. water-vascular ring which has not yet completely encircled the oesophagus; I.e. longitudinal part of ciliated band ; pr.c. prae-oral part of ciliated band.


556


BIPINNARIA.


Miiller differs from him on this point) to remain open throughout. The further changes in the metamorphosis are not considerable. The ciliated bands disappear, and a calcareous ring of ten pieces, five ambulacral and five interambulacral, is formed round the oesophagus. A provisional calcareous skeleton is also developed.

All the embryonic systems of organs pass in this case directly into those of the adult.

The metamorphosis of most Holothuroidea is similar to that just described. In Cucumaria (Selenka) there is however no Auricularia stage, and the uniformly ciliated stage is succeeded by one with five transverse



FIG. 257. THREE STAGES IN THE DEVELOPMENT OF SYNAPTA. A and B are viewed from the ventral surface, and C from the side. (After Metschnikoff.)

m. mouth; oe. oesophagus; pv. walls of the perivisceral cavity; wv. longitudinal vessel of the water- vascular system; p. dorsal pore of water-vascular system; cr. ciliated ring formed round the mouth from parts of the primitive ciliated band.

bands of cilia, and a prae-oral and an anal ciliated cap. The mouth is at first situated ventrally behind the prse-oral cap of cilia, but the prae-oral cap becomes gradually absorbed, and the mouth assumes a terminal position.

In Psolinus (Kowalevsky) there is no embryonic ciliated stage, and the adult condition is attained without even a metamorphosis. There appear to


ECHINODERMATA.


557



be five plates surrounding the mouth, which are developed before any other part of the skeleton, and are regarded by P. H. Carpenter (No. 548) as equivalent to the five oral plates of the Crinoidea. The larval condition with ciliated bands is often spoken of as the pupa stage, and during it the larvae of Holothurians proper use their embryonic tube feet to creep about.

Asteroidea. The commonest and most thoroughly investigated form of Asteroid larva is a free swimming form known as Bipinnaria.

This form in passing from the spherical to the bilateral condition passes through at first almost identical changes to the Auricularian larva. The cilia become at an early period confined to an oral and anal ridge.

The anal ridge gradually extends dorsalwards, and finally forms a complete longitudinal post-oral ring (fig. 259 A) ; the oral ridge also extends dorsalwards, and forms a closed prae-oral ring (fig. 259 A), the space within which is left unshaded in my figure.

The presence of two rings instead of one distinguishes the Bipinnaria from the Auricularia. The two larvae are shewn side by side in fig. 254, and it is obvious that the two bands of the Bipinnaria are (as pointed out by Gegenbaur) equivalent to the single band of the Auricularia divided into two. Ontologically, however, the two bands of Bipinnaria do not appear to arise from the division of a single band.

As the Bipinnaria grows older, a series of arms grows out along lines of the two ciliated bands (fig. 259 C), and, in many cases, three special arms are formed, not connected with the ciliated bands, and covered with warts. These latter arms are


FlG. 258. A LATE STAGE IN THE DEVELOPMENT OF SYNAPTA. (After Metschnikoff.)

The figure shews the vestibular cavity with retracted tentacles ; the ciliated bands ; the water-vascular system, etc.

p. dorsal pore of water-vascular system ; pv. walls of perivisceral cavity; ms. amoeboid cells.


558


BIPINNARIA.


known as brachiolar arms, and the larvae provided with them as Brachiolaria (fig. 259 D).

As a rule the following arms can be distinguished (fig. 259 C and D), on the hinder ring (Agassiz' nomenclature) a median anal pair, a dorsal anal pair, and a ventral anal pair, a dorsal oral pair, and an unpaired anterior dorsal arm ; on the prae-oral ring a ventral oral pair, and sometimes (Miiller) an unpaired anterior ventral arm.

The three brachiolar arms arise as processes from the base of the unpaired dorsal arm, and the two ventral oral arms. The extent of the development of the arms varies with the species.



FIG. 259. DIAGRAMMATIC REPRESENTATION OF VARIOUS FORMS OF ASTEROID LARWE. A, B, C, BIPINNARIA; D, BRACHIOLARIA. (Copied from Muller.) The black lines represent the ciliated bands ; and the shading the space between the prae-oral and the post-oral bands.

m. mouth; an. anus.

The changes by which the Bipinnaria or Brachiolaria becomes converted into the adult starfish are very much more complicated than those which take place in Holothurians. For an accurate knowledge of them we are largely indebted to Alex. Agassiz (No. 543). The development of the starfish takes place entirely at the posterior end of the larva close to the stomach.

On the right and dorsal side of the stomach, and externally to the rig/it peritoneal space, are formed five radially situated calcareous rods arranged in the form of a somewhat irregular pentagon. The surface on which they are deposited has a spiral form, and constitutes together with its calcareous rods, the


ECHINODERMATA. 559


abactinal or dorsal surface of the future starfish. Close to its dorsal, i.e. embryonic dorsal, edge lies the dorsal pore of the water-vascular system (madreporic canal), and close to its ventral edge the anus. On the left and ventral side of the stomach is placed the water-vascular rosette, the development of which was described on p. 549. It is situated on the actinal or ventral surface of the future starfish, and is related to the left peritoneal vesicle.

Metschnikoff (No. 560) and Agassiz (No. 543) differ slightly as to the constitution of the water- vascular rosette. The former describes and figures it as a completely closed rosette, the latter states that ' it does not form a completely closed curve but is always open, forming a sort of twisted crescent-shaped arc.'

The water-vascular rosette is provided with five lobes, corresponding to which are folds in the larval skin, and each lobe corresponds to one of the calcareous plates developed on the abactinal disc. The plane of the actinal surface at first meets that of the abactinal at an acute or nearly right angle. The two surfaces are separated by the whole width of the stomach. The general appearance of the larva from the ventral surface after the development of the water-vascular rosette (i) and abactinal disc (A) is shewn in fig. 260.

As development proceeds the abactinal surface becomes a firm and definite disc, owing to the growth of the original calcareous spicules into more or less definite plates, and to the development of five fresh plates nearer the centre of the disc and interradial in position. Still later a central calcareous plate appears on the abactinal surface, which is thus formed of a central plate, surrounded by a ring of five interradial plates, and then again by a ring of five radial plates. The abactinal disc now also grows out into five short processes, separated by five shallow notches. These processes are the rudiments of the five arms, and each of them corresponds to one of the lobes of the water-vascular rosette. A calcareous deposit is formed round the opening of the water-vascular canal, which becomes the madreporic tubercle 1 . At about this stage the absorption of the larval appendages takes place. The whole anterior part of the

1 The exact position of the madreporic tubercle in relation to the abactinal plates does not seem to have been made out. It might have been anticipated that it would be placed in one of the primary interradial plates, but this does not seem to be the case. The position of the anus is also obscure.


5 6o


BIPINNARIA.



larva with the great prae-oral lobe has hitherto remained unchanged, but now it contracts and undergoes absorption, and becomes completely withdrawn into the disc of the future starfish. The larval mouth is transported into the centre of the actinal disc. In the larvae observed by Agassiz and Metschnikoff nothing was cast off, but the whole absorbed.

According to M tiller and Koren and Danielssen this is not the case in the larva observed by them, but part of the larva is thrown off, and lives for some time independently.

After the absorption of the larval appendages the actinal and abactinal surfaces of the young starfish approach each other, owing to the flattening of the stomach ; at the same time they lose their spiral form, and become flat discs, which fit each other. Each of the lobes of the rosette of the watervascular system becomes one of the radial water-vascular canals. It first becomes five-lobed, each lobe forming a rudimentary tube foot, and on each ^ d ctinal disc of youn Aste ' side of the middle lobe two fresh ones

next spring out, and so on in succession. The terminal median lobe forms the tentacle at the end of the arm, and the eye is developed at its base. The growth of the water-vascular canals keeps pace with that of the arms, and the tube feet become supported at their base by an ingrowth of calcareous matter. The whole of the calcareous skeleton of the larva passes directly into that of the adult, and spines are very soon formed on the plates of the abactinal surface. The original radial plates, together with the spines which they have, are gradually pushed outwards with the growth of the arms by the continual addition of fresh rows of spines between the terminal plate and the plate next to it. It thus comes about that the original radial plates persist at the end of the arms, in connection with the unpaired


FIG. 260. BIPINNARIA LARVA OF AN ASTEROID. (From Gegenbaur ; after Miiller.)

b. mouth ; a. anus ; h. madreporic canal ; t. ambulacral rosette ; c . stomach ; d. g. e. etc. arms of Bipinnaria ; A.


ECHINODERMATA. 561


tentacles which form the apex of the radial water-vascular tubes.

It has already been mentioned that according to Metschnikoff (No. 560) a new oesophagus is formed which perforates the water-vascular ring, and connects the original stomach with the original mouth. Agassiz (No. 543) maintains that the water-vascular ring grows round the primitive oesophagus. He says " During the shrinking of the larva the long oesophagus becomes " shortened and contracted, bringing the opening of the mouth of the larva " to the level of the opening of the oesophagus, which eventually becomes "the true mouth of the starfish." The primitive anus is believed by Metschnikoff to disappear, but by Agassiz to remain. This discrepancy very possibly depends upon these investigators having worked at different species.

There is no doubt that the whole of the larval organs, with the possible exception of the oesophagus, and anus (where absent in the adult), pass directly into the corresponding organs of the starfish and that the prae-oral part of the body and arms of the larva are absorbed and not cast off.

In addition to the Bipinnarian type of Asteroid larva a series of other forms has been described by Miiller (No. 561), Sars, Keren, and Danielssen (No. 554) and other investigators, which are however very imperfectly known. The best-known form is one first of all discovered by Sars in Echinaster Sarsii, and the more or less similar larvae subsequently investigated by Agassiz, Busch, Miiller, Wyville Thomson, etc. of another species of Echinaster and of Asteracanthion. These larvae on leaving the egg have an oval form, and are uniformly covered by cilia. Four processes (or in Agassiz' type one process) grow out from the body ; by these the larvae fix themselves. In the case of Echinaster the larvae are fixed in the ventral concavity of the disc of the mother, between the five arms, where a temporary brood-pouch is established. The main part of the body is converted directly into the disc of the young starfish, while the four processes come to spring from the ventral surface, and are attached to the water- vascular ring. Eventually they atrophy completely. Of the internal structure but little is known ; till the permanent mouth is formed, after the development of the young starfish is pretty well advanced, the stomach has no communication with the exterior.

A second abnormal type of development is presented by the embryo of Pteraster miliaris, as described by Koren and Danielssen 1 . The larvae to the number of eight to twenty develop in a peculiar pouch on the dorsal surface of the body. The early stages are not known, but in the later ones the whole body assumes a pentagonal appearance with a mouth at one edge

1 The following statements are taken from the abstract in Bronn's Thierreichs. B. II. 36


5 62


OPHIUROID PLUTEUS.


of the disc. At a later stage the anus is formed on the dorsal side of an arm opposite the mouth. The stomach is surrounded by a water-vascular ring, from which the madreporic canal passes to the dorsal surface, but does not open. At a later stage the embryonic mouth and anus vanish, to be replaced by a permanent mouth and anus in the normal positions.

A third, and in some respects very curious, form is a worm like larva of Miiller, which is without bands of cilia. The dorsal surface of the youngest larva is divided by transverse constrictions into five segments. On the under side of the first of these is a five-lobed disc, each lobe being provided with a pair of tube feet.

At a later period only three segments are visible on the dorsal surface, but the ventral surface has assumed a pentagonal aspect. The later stages are not known.

Ophiuroidea. The full-grown larva of the Ophiuroids is known as a Pluteus. It commences with the usual more or less spherical form ; from this it passes to a form closely resembling



FIG. 261. DIAGRAMMATIC FIGURES SHEWING THE EVOLUTION OK AN OPHIUROID PLUTEUS FROM A SIMPLE ECHINODERM LARVA. (Copied from Miiller.) The calcareous skeleton is not represented.

///. mouth; an. anus; d. anterior arms; d'. lateral arms; e'. posterior arms; tf. anterolateral arms.

that of Auricularia with a rounded dorsal surface, and a flattened ventral one. Soon however it becomes distinguished by the growth of a post-anal lobe and the absence of a prae-oral lobe (fig. 261 B). The post-anal lobe forms the somewhat rounded apex of the body. In front of the mouth, and between the mouth and anus, arise the anal and oral ciliated ridges, which soon become continued into a single longitudinal ciliated ring. At the same time the body becomes prolonged into a series of


ECHINODERMATA.


563


processes along the ciliated band, which is continued to the extremity of each. The primitive ciliated ring never becomes broken up into two or more rings. A ciliated crown is usually developed at the extremity of the post-anal lobe. The arms are arranged in the form of a ring surrounding the mouth, and are all directed forwards.

The first arms to appear are two lateral ones, which usually remain the most conspicuous (fig. 261 B and C, cf\ Next arises a pair on the sides of the mouth, which may be called the mouth or anterior arms (C, d}. A pair ventral to and behind the lateral arms is then formed, constituting the posterior arms (D, e'\ and finally a pair between the lateral arms and the anterior, constituting the anterolateral arms (D,^).

The concave area between the arms forms the greater part of the ventral surface of the body. Even before the appearance of any of the arms, and before the formation of the mouth, two calcareous rods are formed, which meet behind at the apex of the post-anal lobe, and are continued as a central support into each of the arms as they are successively formed. These rods are shewn at their full development in fig. 262. The important points which distinguish a Pluteus larva from the Auricularia or Bipinnaria are the following :

(i) The presence of the postanal lobe at the hind end of the body. (2) The slight development of a prae-oral lobe. (3) The provisional calcareous skeleton in the larval arms.

Great variations are presented in the development of the arms and provisional skeleton. The presence of lateral arms is however a distinctive characteristic of the Ophiuroid Pluteus. The other arms may be quite absent, but the lateral arms never.

The formation of the permanent Ophiuroid takes place in much the same way as in the Asteroidea.

36-2



FIG. 262. OPHIUROID. after Miiller.)


PLUTEUS LARVA OF AN (From Gegenbaur ;


A. rudiment of young Ophiuroid ; (?. lateral arms; d. anterior arms; e . posterior arms.


564


OPHIUROID PLUTEUS.


There is formed (fig. 262) on the right and dorsal side of stomach the abactinal disc supported by calcareous plates, at first only five in number and radial in position 1 . The disc is at first not symmetrical, but becomes so at the time of the resorption of the larval arms. It grows out into five processes the five future rays. The original five radial plates remain as the terminal segments of the adult rays, and new plates are always added between the ultimate and penultimate plate (Mu'ller), though it is probable that in the later stages fresh plates are added in the disc.

The ventral surface of the permanent Ophiuroid is formed by the concave surface between the mouth and anus. Between this and the stomach is



FIG. 263. DIAGRAMMATIC FIGURES SHEWING THE EVOLUTION OF ECHINOID PLUTEI. (Copied from Miiller.) The calcareous skeleton is not represented. E. Pluteus of Spatangus.

m. mouth; an. anus; d. anterior arms; d' . point where lateral arms arise in the Ophiuroid Pluteus; e. anterointernal arms; e. posterior arms; g'. anterolateral arms; g. anteroexternal arms.

situated the water-vascular ring. It is at first not closed, but is horseshoeshaped, with five blind appendages (fig. 262). It eventually grows round the cesophagus, which, together with the larval mouth, is retained in the adult. The five blind appendages become themselves lobed in the same way as in Asterias, and grow out along the five arms of the disc and become the radial canals and tentacles. All these parts of the water-vascular system are of course covered by skin, and probably also surrounded by mesoblast cells, in which at a later period the calcareous plates which lie ventral to the radial canal are formed. The larval anus disappears. As long as the larval appendages are not absorbed the ventral and dorsal discs of the permanent Ophiuroid fit as little as in the case of the Brachiolaria, but at a certain period the appendages are absorbed. The calcareous rods of the larval arms

1 Whether interradial plates are developed as in Asterias is not clear. They seem to be found in Ophiopholis bellis, Agassiz, but have not been recognised in other forms (vide Carpenter, No. 548, p. 369).


ECHINODERMATA. 565


break up, the arms and anal lobe become absorbed, and the dorsal and ventral discs, with the intervening stomach and other organs, are alone left. After this the discs fit together, and there is thus formed a complete young Ophiuroid.

The whole of the internal organs of the larva (except the anus), including the mouth, cesophagus, the body cavity, etc. are carried on directly into the adult.

The larval skeleton is, as above stated, absorbed.

The viviparous larva of Amphiura squamata does not differ very greatly from the larvae with very imperfect arms. It does not develop a distinct ciliated band, and the provisional skeleton is very imperfect. The absence of these parts, as well as of the anus, mentioned on p. 549, may probably be correlated with the viviparous habits of the larva. With reference to the passage of this larva into the adult there is practically nothing to add to what has just been stated. When the development of the adult is fairly advanced the part of the body with the provisional skeleton forms an elongated rod-like process attached to the developing disc. It becomes eventually absorbed.

Echinoidea. The Echinus larva (fig. 263} has a Pluteus form like that of the Ophiuroids, and in most points, such as the



FIG. 264. Two LARV/E OF STRONGYLOCENTRUS. (From Agassiz.) m. mouth; a. anus; o. cesophagus; d. stomach; c. intestine; '. and v. ciliated ridges; iv. water- vascular tube; r. calcareous rods.

presence of the anal lobe, the ciliated band, the provisional skeleton, etc., develops in the same manner. The chief difference between the two Pluteus forms concerns the development of the lateral arms. These, which form the most prominent arms in the Ophiuroid Pluteus, are entirely absent in the Echinoid


5 66


ECHINOID PLUTEUS.


Pluteus, which accordingly has, as a rule, a much narrower form than the Ophiuroid Pluteus.

A pair of ciliated epaulettes on each side of and behind the ciliated ring is very characteristic of some Echinoid larvae. They are originally developed from the ciliated ring (fig. 266 A



FIG. 265. LATERAL AND VENTRAL VIEW OF A LARVA OF STRONGYLOCENTRUS.

(From Agassiz.) General references as in fig. 264.

b. dorsal opening of madreporic canal; e '. posterior arms ; e'". anterior arms; f lV . anterointernal arms.

and B, z>"). The presence of three processes from the anal lobe supported by calcareous rods is characteristic of the Spatangoid Pluteus (fig. 263 E).

The first two pairs of arms to develop, employing the same names as in Ophiuroids, are the anterior attached to the oral process (fig. 263 C, d] and the posterior pair (*?') A pair of anterolateral arms next becomes developed (j^). A fourth pair (not represented in Ophiuroids) appears on the inner side of the anterior pair forming an anterointernal pair (e}, and in the Spatangoid Pluteus a fifth pair may be added on the external side of the anterior pair forming an anteroexternal pair (g).

Each of the first-formed paired calcareous rods is composed of three processes, two of which extend into the anterior and posterior arms ; and the third and strongest passes into the anal lobe, and there meets its fellow (fig. 265). A transverse bar in front of the arms joins the rods of the two sides meeting them at the point where the three processes diverge. The process in the anterolateral arm (fig. 266 B) is at first independent of this system of rods, but eventually unites with it. Although our knowledge of


ECHINODERMATA. 567


the Pluteus types in the different groups is not sufficient to generalise with great confidence, a few points seem to have been fairly determined 1 . The Plutei of Strongylocentrus (figs. 266 and 267) and Echinus have eight arms and four ciliated epaulettes. The only Cidaris-like form, the Pluteus of which is known, is Arbacia : it presents certain peculiarities. The anal lobe develops a pair of posterior (auricular) appendages, and the ciliated ring, besides growing out into the normal eight appendages, has a pair of short blunt anterior and posterior lobes. An extra pair of non-ciliated accessory mouth arms appears also to be developed. Ciliated epaulettes are not present. So far as is known the Clypeastroid larva is chiefly characterized by the round form of the anal lobe. The calcareous rods are latticed. In the Pluteus of Spatangoids there are (fig. 263) five pairs of arms around the mouth pointing forwards, and three arms developed from the anal lobe pointing backwards. One of these is unpaired, and starts from the apex of the anal lobe. All the arms have calcareous rods which, in the case of the posterior pair, the anterolateral pair, and the unpaired arm of the anal lobe, are latticed. Ciliated epaulettes are not developed.

Viviparous larvae of Echinoids have been described by Agassiz 2 .

The development of the permanent Echinus has been chiefly worked out by Agassiz and Metschnikoff.

In the Pluteus of Echinus lividus the first indication of the adult arises, when three pairs of arms are already developed, as an invagination of the skin on the left side, between the posterior and anterolateral arms, the bottom of which is placed close to the water-vascular vesicle (fig. 266 B, u/\ The base of this invagination becomes very thick, and forms the ventral disc of the future Echinus. The parts connecting this disc with the external skin become however thin, and, on the narrowing of the external aperture of invagination and the growth of the thickened disc, constitute a covering for the disc, called by Metschnikoff the amnion. The water- vascular vesicle adjoining this disc grows out into five processes, forming as many tube feet, which cause the surface of the involuted disc to be produced into the same number of processes. The external opening of the invagination of the disc never closes, and after the development of the tube feet begins to widen again, and the amnion to atrophy. Through the opening of the invagination the tube feet now project. The dorsal and right surface of the Pluteus, which extends so as to embrace the opening of the madreporic canal and the anus, forms the abactinal or dorsal surface of the future Echinus (fig. 267, a). This disc fits on to the actinal invaginated surface which arises on the left side of the Pluteus. On the right surface of the larva (dorsal of permanent Echinus) two pedicellariae appear, and at a later period spines are formed, which are at first arranged in a ring-like form round the edge of the primitively flat test. While these changes are taking place, and the two surfaces of the future Echinus are gradually moulding themselves so as to

1 Vide especially Muller, Agassiz, and Metschnikoff.

2 For viviparous Echini vide Agassiz, Proc. Amer. Acad. 1876.


5 68


ECHINOID PLUTEUS.


form what is obviously a young Echinus, the arms of the Pluteus with their contained skeleton have been gradually undergoing atrophy. They become irregular in form, their contained skeleton breaks up into small pieces, and they are gradually absorbed.

The water-vascular ring is from the first complete, so that, as in Asterias, it is perforated through the centre by a new oesophagus. According



FIG. 266. SIDE AND DORSAL VIEW OF A LARVA OF STRONGYLOCENTRUS.

(From Agassiz.) General reference letters as in figs. 264 and 265. e" . anterolateral arms; v" '. ciliated epaulettes; ?&'. invagination to form the disc of Echinus.

to Agassiz the first five tentacles or tube feet grow into the radial canals, and form the odd terminal tentacles exactly as in Asterias 1 . Spatangus only differs in development from Echinus in the fact that the opening of the invagination to form the ventral disc becomes completely closed, and that the tube feet have eventually to force their way through the larval epidermis of the amnion, which is ruptured in the process and eventually thrown off.

Crinoidea. The larva of Antedon, while still within the egg-shell, assumes an oval form and uniform ciliation. Before it

1 Gotte (No. 549) supported by Muller's and Krohn's older, and in some points extremely erroneous observations, has enunciated the view that the radial canals in Echinoids and Holothuroids have a different nature from those in Asteroids and Ophiuroids.


ECHINODERMATA.


569


becomes hatched the uniform layer of cilia is replaced by four transverse bands of cilia, and a tuft of cilia at the posterior extremity. In this condition it escapes from the egg-shell



FIG. 267. FULL-GROWN LARVA OF STRONGYLOCENTRUS. (From Agassiz.) The figure shews the largely-developed abactinal disc of the young Echinus enclosing the larval stomach. Reference letters as in previous figs.

(fig. 268 A), and becomes bilateral, owing to a flattening of the ventral surface. On the flattened surface appears a ciliated


570


CRINOID LARVA.


depression corresponding in position with the now closed blastopore (vide p. 550). The third ciliated band bends forward to pass in front of this (fig. 269). Behind the last ciliated band there is present a small depression of unknown function, also



FIG. 768. THREB STAGES IN THE DEVELOPMENT OF ANTEDON (COMATULA.)

(From Lubbock; after Thomson.)

A. larva just hatched; B. larva with rudiment of the calcareous plates; C. Pentacrinoid larva.


ECHINODERMATA.


571


situated on the ventral surface. The posterior extremity of the embryo elongates to form the rudiment of the future stem, and a fresh depression, marking the position of the future mouth, makes its appearance on the anterior and ventral part.

While the ciliated bands are still at their full development, the calcareous skeleton of the future calyx makes its appearance in the form of two rows, each of five plates, formed of a network of spicula (figs. 268 B and 269). The plates of the anterior ring are known as the orals, those of the posterior as the basals. The former surround the left, i.e. anterior peritoneal sack ; the latter the right, i.e. posterior peritoneal sack. The two rows of plates are at first not quite transverse, but form two oblique circles, the dorsal end being in advance of the ventral. The rows soon become transverse, while the originally somewhat ventral oral surface is carried into the centre of the area enclosed by the oral plates.

By the change in position of the original ventral surface relatively to the axis of the body, the bilateral symmetry of the larva passes into a radial symmetry. While the first skeletal elements of the calyx are being formed, the skeleton of the stem is also established. The terminal plate is first of all established, then the joints, eight at first, of the stem. The centro-dorsal plate is stated by Thomson to be formed as the uppermost joint of the stem 1 . The larva, after the completion of the above changes, is shewn in fig. 268 B, and somewhat more diagrammatically in fig. 269.

After the above elements of the skeleton have become established the ciliated bands undergo atrophy, and shortly after 1 Gotte (No. 549) on the other hand holds that the centro-dorsal plate is developed by the coalescence of a series of at first independent rods, which originate simultaneously with, and close to, the lower edges of the basals, and that it is therefore similar in its origin to the basals.



FIG. 269. LARVA OF ANTEDON WITH RUDIMENTS OF CALCAREOUS SKELETON. (From Carpenter; after Thomson.)

i. Terminal plate at the end of the stem ; 3. basals ; or. orals ; bl. position of blastopore.


572


CRINOID LARVA.


wards the larva becomes attached by the terminal plate of its stem. It then passes into the Pentacrinoid stage! The larva in this stage is shewn in fig. 268 C and fig. 270. New joints are added at the upper end of the stem next the calyx, and a new element the radials makes its appearance as a ring of five small plates, placed in the space between the basals and orals, and in the intervals alternating with them (fig. 270, 4). The roof of the oral vestibule (vide fig. 253 and p. 551) has in the meantime become ruptured ; and the external opening of the mouth thus becomes established. Surrounding the mouth are five petal-like lobes, each of them supported by an oral plate (fig. 268 C). In the intervals between them five branched and highly contractile tentacles, which were previously enclosed within the vestibule, now sprout out : they mark the position of the future radial canals, and are outgrowths of the water-vascular ring. At the base of each of them a pair of additional tentacles is soon formed. Each primary tentacle corresponds to one of the radials. These latter are therefore, as their name implies, radial in position; while the basals and orals are interradial. In addition to the contractile radial tentacles ten non-contractile tentacles, also diverticula of the water- vascular ring, are soon formed, two for each interradius.

In the course of the further development the equatorial space between the FlG - 2 7<>. YOUNG PEN . TACRINOID LARVA OF AN

orals and the basals enlarges, and gives TEDON. (From Carpenter ; rise to a wide oral disc, the sides of which after w >' ville Thom s"-)

- , , . ... . i. terminal plate of stem;

are formed by the radials resting on the c d. centro-donal plate; 3 . basals; while in the centre of it are bftsals J 4- radials; or. orals. placed the five orals, each with its special lobe.

The anus, which is formed on the ventral side in the position



ECHINODERMATA. 573


of the blastopore (p. 551), becomes surrounded by an anal plate, which is interradial in position, and lies on the surface of the oral disc between the orals and radials. On the oral plate in the next interradius is placed the opening of a single funnel leading into the body cavity, which Ludwig regards as equivalent to the opening of the madreporic canal (vide p. 55 1) 1 .

From the edge of the vestibule the arms grow out, carrying with them the tentacular prolongation of the water-vascular ring. Two additional rows of radials are soon added.

The stalked Pentacrinoid larva becomes converted, on the absorption of the stalk, into the adult Antedon. The stalk is functionally replaced by a number of short cirri springing from the centro-dorsal plate. The five basals coalesce into a single plate, known as the rosette, and the five orals disappear, though the lobes on which they were placed persist. In some stalked forms, e.g. Rhizocrinus Hyocrinus, the orals are permanently retained. The arms bifurcate at the end of the third radial, and the first radial becomes in Antedon rosacea (though not in all species of Antedon) concealed from the surface by the growth of the centro-dorsal plate. An immense number of funnels, leading into the body cavity, are formed in addition to the single one present in the young larva. These are regarded by Ludwig as equivalent to so many openings of the madreporic canal ; and there are developed, in correspondence with them, diverticula of the water-vascular ring.

Comparison of Echinoderm Larvce and General Conclusions.

In any comparison of the various types of Echinoderm larvae it is necessary to distinguish between the free-swimming forms, and the viviparous or fixed forms. A very superficial examination suffices to shew that the free-swimming forms agree very much more closely amongst themselves than the viviparous

1 I have made no attempt to discuss the homologies of the plates of the larval Echinodermata because the criteria for such a discussion are still in dispute. The suggestive memoirs of P. H. Carpenter (No. 548) on this subject may be consulted by the reader. Carpenter attempts to found his homologies on the relation of the plates to the primitive peritoneal vesicles, and I am inclined to believe that this method of dealing with these homologies is the right one. Ludwig (No. 559) by regarding the opening of the madreporic canal as a fixed point has arrived at very different results.


574


COMPARISON OF ECHINODERM LARV.-E.


forms. We are therefore justified in concluding that in the viviparous forms the development is abbreviated and modified.

All the free forms are nearly alike in their earliest stage after the formation of the archenteron. The surface between the anus and the future mouth becomes flattened, and (except in Antedon, Cucumaria, Psolinus, etc. which practically have an abbreviated development like that of the viviparous forms) a ridge of cilia becomes established in front of the mouth, and a second ridge between the mouth and the anus. This larval form, which is shewn in fig. 264 A, is the type from which the various forms of Echinoderm larvae start.

In all cases, except in Bipinnaria, the two ciliated ridges soon become united, and constitute a single longitudinal postoral ciliated ring.

The larvae in their further growth undergo various changes, and in the later stages they may be divided into two groups :

(1) The Pluteus larva of Echinoids and Ophiuroids.

(2) The Auricularia (Holothuroids) and Bipinnaria (Asteroids) type.

The first group is characterized by the growth of a number of arms more or less surrounding the mouth, and supported by calcareous rods. The ciliated band retains its primitive condition as a simple longitudinal band throughout larval life. There is a very small prae-oral lobe, while an anal lobe is very largely developed.

The Auricularia and Bi- A. B

pinnaria resemble each other in shape, in the development of a large prae-oral lobe, and in the absence of provisional calcareous rods ; but differ in the fact that the ciliated band is single in Auricularia (fig 271 A), and is double in Bipinnaria (fig. 271 B).

TheBipinnarialarvashews

THUROID. B. THE LARVA OF AN ASTEa great tendency to develop RIAS.

soft arms; while in the Auri- . ' mouth; st. stomach; a. anus; I.e. , . ,_, , *_ 1-1- primitive longitudinal ciliated band; pr.c.

cularia the longitudinal ciliat- p r3 e-oral ciliated band.



FlG


THE LARVA OF A


ECHINODERMATA. 575


ed band breaks up into a number of transverse ciliated bands. This condition is in .some instances reached directly, and such larvae undoubtedly approximate to the larvae of Antedon, in which the uniformly ciliated condition is succeeded by one with four transverse bands, of which one is prae-oral.

All or nearly all Echinoderm larvae are bilaterally symmetrical, and since all Echinodermata eventually attain a radial symmetry, a change necessarily takes place from the bilateral to the radial type.

In the case of the Holothurians and Antedon, and generally in the viviparous types, this change is more or less completely effected in the embryonic condition ; but in the Bipinnaria and Pluteus types a radial symmetry does not become apparent till after the absorption of the larval appendages. It is a remarkable fact, which seems to hold for the Asteroids, Ophiuroids, Echinoids, and Crinoids, that the dorsal side of the larva is not directly converted into the dorsal disc of the adult; but the dorsal and right side becomes the adult dorsal or abactinal surface, while the ventral and left becomes the actinal or ventral surface.

It is interesting to note with reference to the larvae of the Echinodermata that the various existing types of larvae must have been formed after the differentiation of the existing groups of the Echinodermata ; otherwise it would be necessary to adopt the impossible position that the different groups of Echinodermata were severally descended from the different types of larvae. The various special appendages, etc. of the different larvae have therefore a purely secondary significance; and their atrophy at the time of the passage of the larva into the adult, which is nothing else but a complicated metamorphosis, is easily explained.

Originally, no doubt, the transition from the larva to the adult was very simple, as it is at present in most Holothurians ; but as the larvae developed various provisional appendages, it became necessary that these should be absorbed in the passage to the adult state.

It would obviously be advantageous that their absorption should be as rapid as possible, since the larva in a state of transition to the adult would be in a very disadvantageous


576 COMPARISON OF ECHINODERM

position. The rapid metamorphosis, which we find in Asteroids, Ophiuroids, and Echinoids in the passage from the larval to the adult state, has no doubt arisen for this reason.

In spite of the varying provisional appendages possessed by Echinoderm larvae it is possible, as stated above (p. 574), to recognise a type of larva, of which all the existing Echinoderm larval forms are modifications. This type does not appear to me to be closely related to that of the larvae of any group described in the preceding pages. It has no doubt certain resemblances to the trochosphere larva of Chaetopoda, Mollusca, etc., but the differences between the two types are more striking than the resemblances. It firstly differs from the trochosphere larva in the character of the ciliation. Both larvae start from the uniformly ciliated condition, but while the prae-oral ring is almost invariable, and a peri-anal ring very common in the trochosphere; in the Echinoderm larva such rings are rarely found ; and even when present, i.e. the prae-oral ring of Bipinnaria and the terminal though hardly peri-anal patch of Antedon, do not resemble closely the more or less similar structures of the trochosphere. The two ciliated ridges (fig. 264 A) common to all the Echinoderm larvae, and subsequently continued into a longitudinal ring, have not yet been found in any trochosphere. The transverse ciliated rings of the Holothurian and Crinoid larvae are of no importance in the comparison between the trochosphere larvae and the larvae of Echinodermata, since such rings are frequently secondarily developed. Cf. Pneumodermon and Dentalium amongst Mollusca.

In the character of the prae-oral lobe the two types again differ. Though the prae-oral lobe is often found in Echinoderm larvae it is never the seat of an important (supra-oesophageal) ganglion and organs of special sense, as it invariably is in the trochosphere.

Nothing like the vaso-peritoneal vesicles of the Echinoderm larvae has been found in the trochosphere ; nor have the characteristic trochosphere excretory organs been found in the Echinoderm larvae.

The larva which most nearly approaches those of the Echinodermata is the larva of Balanoglossus described in the next chapter.


ECHINODERMATA. 577


BIBLIOGRAPHY.

(542) Alex. Agassiz. Revision of the Echini. Cambridge, U.S. 1872 74.

(543) Alex. Agassiz. " North American Starfishes." Memoirs of the Museum of Comparative Anatomy and Zoology at Harvard College, Vol. v., No. i. 1877 (originally published in 1864).

(544) J. Barrois. " Embryogenie de 1'Asteriscus verruculatus " Journal dc VAnat. et Phys. 1879.

(545) A. Baur. Beitrdge zur Naturgeschichte d. Synapta digitata. Dresden, 1864.

(546) H. G. Bronn. Klassen u. Ordnungen etc. Strahlenthiere, Vol. II. 1860.

(547) W. B. Carpenter. "Researches on the structure, physiology and development of Antedon." Phil. Trans. CLVI. 1866, and Proceedings of the Roy. Soc., No. 166. 1876.

(548) P. H. Carpenter. " On the oral and apical systems of the Echinoderms." Quart. J. of Micr. Science, Vol. xvm. and xix. 18789.

(549) A. Gotte. " Vergleichende Entwicklungsgeschichte d. Comatula mediterranea." Arch, fur micr. Anat., Vol. xn. 1876.

(550) R. Greeff. "Ueber die Entwicklung des Asteracanthion rubens vom Ei bis zur Bipinnaria u. Brachiolaria." Schriften d. Gesellschaft zur Beforderung d. gesammten Natunvissenschaften zu Marburg, Bd. xn. 1876.

(551) R. Greeff. "Ueber den Bau u. die Entwicklung d. Echinodermen." Sitz. d. Gesell. z. Beforderung d. gesam. Naturwiss. zu Marburg, No. 4. 1879.

(552) T. H. Huxley. "Report upon the researches of Miiller into the anat. anddevel. of the Echinoderms." Ann. and Mag. of Nat. Hist., 2nd Ser., Vol. vin. 1851.

(553) Koren and Danielssen. "Observations sur la Bipinnaria asterigera. Ann. Scien. Nat., Ser. in., Vol. vii. 1847.

(554) Koren and Danielssen. "Observations on the development of the Starfishes." Ann. and Mag. of Nat. Hist., Vol. XX. 1857.

(555) A. Kowalevsky. " Entwicklungsgeschichte d. Holothurien. " Mhn.Ac. Petersbourg, Ser. VII., Tom. XL, No. 6.

(556) A. Krohn. "Beobacht. a. d. Entwick. d. Holothurien u. Seeigel." Miillers Archiv, 1851.

(557) A. Krohn. "Ueb. d. Entwick. d. Seesterne u. Holothurien." Miillcr's Archiv, 1853.

(558) A. Krohn. "Beobacht. lib. Echinodermenlarven." Mailer's Archiv, 1854.

(559) H. Ludwig. "Ueb. d. primar. Steinkanal d. Crinoideen, nebst vergl. anat. Bemerk. lib. d. Echinodermen." Zeit.f. wiss. ZooL, Vol. xxxiv. 1880.

(560) E. Metschnikoff. "Studien iib. d. Entwick. d. Echinodermen u. Nemertinen." Mem. Ac. Petersboiirg, Series vii., Tom. xiv., No. 8. 1869.

(561) 1 Joh. Miiller. "Ueb. d. Larven u. d. Metamorphosed. Echinodermen." Abhandlungen d. Berlin. Akad. (Five Memoirs), 1848, 49, 50, 52 (two Memoirs).

(562) Joh. Mtiller. "Allgemeiner Plan d. Entwicklung d. Echinodermen." Abhandl. d. Berlin. Akad., 1853.

1 The dates in this reference are the dates of publication. B. II. 37


578 BIBLIOGRAPHY.


(563) E. Selenka. "Zur Entwicklung d. Holothurien." Zeit. f. wiss. Zool., Bd. xxvii. 1876.

(564) E. Selenka. "Keimblatter u. Organanlage bei Echiniden." Zeit.f.-wiss. Zool., Vol. xxxin. 1879.

(565) Sir Wyville Thomson. "On the Embryology of the Echinodermata." Natural History Review, 1 864.

(566) Sir Wyville Thomson. "On the Embryogeny of Antedon rosaceus." Phil. Trans. 1865.


CHAPTER XXI.


ENTEROPNEUSTA.


THE larva of Balanoglossus is known as Tornaria. The prselarval development is not known, and the youngest stage (fig. 272) so far described (Gotte, No. 569) has many remarkable points of resemblance to a young Bipinnaria.

A mouth (m\ situated on the ventral surface, leads into an alimentary canal with a terminal anus (an). A prae-oral lobe is well developed, as in Bipinnaria, but there is no post-anal lobe. The bands of cilia have the same general form as in Bipinnaria. There is a prae-oral band, and a longitudinal post-oral band ; and the two bands nearly meet at the apex of the praeoral lobe (fig. 273). A contractile band



an

FIG. 272. EARLY STAGE IN THE DEVELOPMENT OF TORNARIA. (After Gotte.)

W. so-called watervascular vesicle developing as an outgrowth of the mesenteron; m.

passes from the oesophagus to the apex of mouth; an. anus, the prae-oral lobe, and a diverticulum (fig. 272, W) from the alimentary tract, directed towards the dorsal surface, is present. Contractile cells are scattered in the space between the body wall and the gut.

In the following stage (fig. 274 A) a conspicuous transverse post-oral band of a single row of long cilia is formed, and the original bands become more sinuous. The alimentary diverticulum of the last stage becomes an independent vesicle opening by a pore on the dorsal surface (fig. 274 A, w). The contractile cord is now inserted on this vesicle. Where this cord joins the apex of the prae-oral lobe between the two anterior bands of cilia a thickening of the epiblast (? a ganglion) has become

372


580


ENTEROPNEUSTA.



C.C.


an.

FIG. 273. YOUNG TORNARIA.

(After Miiller.)

m. mouth ; an. anus ; w. watervascular vesicle ; oc. eye-spots ; c.c. contractile cord.


established, and on it are placed two eye-spots (fig. 273 oc, and fig. 274 A). A deep bay is formed on the ventral surface of the larva.

As the larva grows older the original bands of cilia become more sinuous, and a second transverse band with small cilia is formed (in the Mediterranean larva) between the previous transverse band and the anus. The water-vascular vesicle is prolonged into two spurs, one on each side of the stomach. A pulsating vesicle or heart is also formed (fig. 274 B, ht), and arises, according to Spcngel (No. 572), as a thickening of the epidermis. It subsequently becomes enveloped in a pericardium, and is placed in a depression in the water-vascular vesicle. Two pairs of diverticula, one behind the other, grow out (Agassiz, No. 568) from the gastric region of the alimentary canal. The two parts of each pair form flattened compartments, which together give rise to a complete investment of the adjoining parts of the alimentary tract. The two parts of each coalesce, and thus form



FlG. 274. TWO STAGKS IN THK 1 >KY KI.< >I'M KN I

OF TORNARIA. (After Metschnikoff.)

The black lines represent the ciliated hands. m. mouth; an. anus; br. branchial cleft; ///.

heart ; c. Ixxly cavity between splanchnic and

somatic mesoblast layers; 7.-'. watcr-vascvilar vesicle:

v. circular blood-vessel.


ENTEROPNEUSTA.


5 8l


a double-walled cylinder round the alimentary tract, but their cavities remain separated by a dorsal and ventral septum.

Eventually (Spengel) the cavity of the anterior cylinder forms the section of the body cavity in the collar of the adult, and that of the posterior (fig. 274 B, c) the remainder of the body cavity. The septa, separating the two halves of each, remain as dorsal and ventral mesenteries.

The conversion of Tornaria (fig. 274 A) into Balanoglossus (fig. 274 B) is effected in a few hours, and consists mainly in certain changes in configuration, and in the disappearance of the longitudinal ciliated band.

The body of the young Balanoglossus (fig. 274 B) is divided into three regions (i) the proboscidian region, (2) the collar, (3) the trunk proper. The proboscidian region is formed by the elongation of the prae-oral lobe into an oval body with the eyespots at its extremity, and provided with strong longitudinal muscles. The heart (hi) and water-vascular vesicle lie near its base, but the contractile cord connected with the latter is no longer present. The mouth is placed on the ventral side at the base of the prae-oral lobe, and immediately behind it is the collar. The remainder of the body is more or less conical, and is still girt with the larval transverse ciliated band, which lies in the middle of the gastric region in the Mediterranean species, but in the cesophageal region in the American one.

The whole of the body, including the proboscis, becomes richly ciliated.

One of the most important cha- S us WITH FOUR BRANCHIAL racters of the adult Balanoglossus CLEFTS * (After Alex. Agossiz.)

r . m. mouth ; an. anus ; br. bran consists in the presence of respira- chial cleft . hL heart ; IV. watertory structures comparable with the vascular vesicle, vertebrate gill slits. The earliest traces of these structures are distinctly formed while the larva is still in the Tornaria



FIG. 275. LATE STAGE IN THE DEVELOPMENT OF BALANOGLOS


582 I'N I'KUOl'NKUSTA.


condition, as one pair of pouches from the oesophagus in the Mediterranean species, and four pairs in the American one (fig. 275, br).

In the Mediterranean Tornaria the two pouches meet the skin dorsally, and in the young Balanoglossus (fig. 274 B, br) acquire an external opening on the dorsal side. In the American species the first four pouches are without external openings till additional pouches have been formed. Fresh gill pouches continue to be formed both in the American and probably the Mediterranean species, but the conversion of the simple pouches into the complicated gill structure of the adult has only been studied by Agassiz (No. 568) in the American species. It would seem in the first place that the structure of the adult gill slits is much less complicated in the American than in the Mediterranean species. The simple pouches of the young become fairly numerous. They are at first circular ; they then become elliptical, and the dorsal wall of each slit becomes folded ; subsequently fresh folds are formed which greatly increase the complexity of the gills. The external openings are not acquired till comparatively late.

Our knowledge of the development of the internal organs, mainly derived from Agassiz, is still imperfect. The vascular system appears early in the form of a dorsal and a ventral vessel, both pointed, and apparently ending blindly at their two extremities. The two spurs of the water-vascular vesicle, which in the Tornaria stage rested upon the stomach, now grow round the oesophagus, and form an anterior vascular ring, which Agassiz describes as becoming connected with the heart, though it still communicates with the exterior by the dorsal pore and seems to become connected with the remainder of the vascular system. According to Spengel (No. 572) the dorsal vessel becomes connected with the heart, which remains through life in the proboscis : the cavity of the water-vascular vesicle forms the cavity of the proboscis in the adult, and its pore remains as a dorsal (not, as usually stated, ventral) pore leading to the exterior.

The eye-spots disappear.

Tornaria is a very interesting larval form, since it is intermediate in structure between the larva of an Echinoderm and trochosphere type common to the Mollusca, Chxtopoda, etc. The shape of the body especially the form of the ventral depression, the character of the longitudinal ciliated band, the structure and derivation of the water-vascular vesicle, and the


ENTEROPNEUSTA. 583


formation of the walls of the body cavity as gastric diverticula, are all characters which point to a connection with Echinodcrm larvae.

On the other hand the eye-spots at the end of the prae-oral lobe 1 , the contractile band passing from the oesophagus to the eye-spots (fig. 273), the two posterior bands of cilia, and the terminal anus are all trochosphere characters.

The persistence of the prae-oral lobe as the proboscis is interesting, as tending to shew that Balanoglossus is the surviving representative of a primitive group.

BIBLIOGRAPHY.

(567) A. Agassiz. "Tornaria." Ann. Lyceum Nat. Hist.\u\. New York, 1866.

(568) A. Agassiz. "The History of Balanoglossus and Tornaria." Mem. Amer. Acad. of Arts and Stien., Vol. IX. 1873.

(569) A. Gotte. " Entwicklangsgeschichte d. Comatula Mediterranea." Archiv fur mikr. Anat., Bd. xii., 1876, p. 641.

(570) E. Metschnikoff. " Untersuchungen iib d. Metamorphose, etc. (Tornaria)." Zeit.fiir wiss. ZooL, Bd. xx. 1870.

(571) J. M tiller. " Ueb. d. Larven u. Metamor. d. Echinodermen." Berlin Akad., 1849 and 1850.

(572) J. W. Spengel. "Ban u. Entwicklung von Balanoglossus. Tagebl. d. Naturf. Vers. Miinchen, 1877.

1 It would be interesting to have further information about the fate of the thickening of epiblast in the vicinity of the eye-spots. The thickening should by rights be the supra-oesophageal ganglion, and it does not seem absolutely impossible that it may give rise to the dorso-median cord in the region of the collar, which constitutes, according to Spengel, the main ganglion of the adult.


INDEX.


Abdominalia, 459, 493, 499

Acanthocephala, 379

Acanthosoma, 473, 474, 475

Acarina, 444, 454

Accipenser, 102

Achaeta, 319

Achelia, 538

Achtheres percarum, 490

Acineta, 7, 8

Acraspeda, 152, 165, 167, 178, 179, 182,

185, 186

Actinia, 169, 171, 179 Actinophrys, 9

Actinotrocha, 315, 318, 363, 364 Actinozoa, 26, 102, 152, j66, 170, 171,

172, 176, 178, 179, 181, 182, 186 Actinula, 155 Aculeata, 421 ^Egineta flavescens, 158 yEginidae, 156, 158 ^Eginopsis Mediterranea, 158 /Equorea Mitrocoma, 182 Agalma, 163 Agelena, 436, 450 Agelena labyrinthica, 119, 438 Alciope, 74 Alcippidae, 499 Alcyonaria, 152 Alcyonidse, 167, 168 Alcyonidium mytili, 297, 300, 302 Alcyonium palmatum, 119, 148, 167, 182 Alima, 484, 486 Amoeba, 19, 20 Amphibia, 22, 54, 56, 59, 60, 63, 66, 74,

83, 102

Amphilina, 218

Amphioxus, 54, 56, 59, 61, 66, 93, 426 Amphipoda, 518 Amphiporus lactifloreus, 202 Amphistomum, 31

,, subclavatum, 205

Amphitrochae, 330 Amphiura squamata, 565


Anchorella, 108, 492, 520

Anelasma squalicola, 499

Anguillulidse, 371

Annelida, 14, 25, 98, 503, 525

Anodon, 37, 38, 39, 100, 107, 259, 260,

265, 266, 268 Anopla, 189, 202 Anura, 5

Antedon, 568, 573, 574 Aphides, 15, 16, 76, 79, 116, 428, 429 Aphrodite, 42

Apis, 402, 407, 408, 412, 413 Aplysia, 99, 226, 238, 252, 253 Aplysinidaa, 146 Apoda, 459, 493 Aptera, 395, 420 Apus, 1 6, 79, 460, 463 Arachnida, 22, 114, 119, 413, 4.51, 435,

444, 454, 455, 458, 537, 539 Arachnitis, 171 Araneina, 50, 51, 436 Arbacia, 567 Area, 38 Archigetes, 218 Archizosea gigas, 494 Arenicola, 42

Argiope, 311, 312, 315, 317 Argonauta, 247, 248 Argulus, 492 Armata, 355 Arthropoda, 12, 16, 18, 22, 75, 77,79, 83,

108, no, 221, 382, 383, 434, 448,503,

5 2 5> 534 54', 54 2 Articulata, 311, 313, 316, 317 Ascaridiae, 371 Ascaris nigrovenosa, 16, 82

,, lumbricoides, 375 Ascetta, 144 Ascidia canina, 53 Ascidians, 74, 102, 208, 426 Asellus aquaticus, 112,120, 516 Astacus, 66, 465, 477, 511, 512, 513,

525


586


INDKX.


Asteracanthion, 69, 70, 561

Asterias, 20, 68, 69, 71, 78, 80, 84, 549,

564 Asteroidea, 35, 36, 544, 549, 557, 563,

576 Astnea, 169

Astroides, 169

Atax Bonzi, 445

Atlanta, 231, 240

Atrochae, 330

Aurelia, 167

Auricularia, 553, 554, 562, 574

Autolytus cornutus, 319, 343

Aves, 56, 59, 61, 64, 107. 109

Axolotl, 1 6

Balanoglossus, 576, 579, 581

Balanus balanoides, 75, 493

Belemnites, 252, 253

Bipinnaria, 557, 563, 574, 576, 579

Blatta, 374, 395

Bojanus, organ of, 264, 282

Bonellia, 20, 43, 44, 98, 324, 355, 358,

359 Bothriocephalus salmonis, 211

,, proboscideus, 212

Brachiella, 492 Brachiolaria, 558, 564 Brachiopoda, 311, 317, 318 Brachyura, 466, 480, 483 Branchiobdella, 42, 43, 346 Branchiogasteropoda, 272 Branchiopoda, 79, 459, 523, 524 Branchipus, 463, 524 Branchiura, 459, 492 Branchionus urceolaris, 221 Braula, 396 Uuccinum, 237, 280 Bulimus citrinus, 229 Bunodes, 169, 171 Buthus, 431

Calcispongiae, 138, 148

Calopteryx, 402

Calycophoridce, 152, 159

Calyptoblastic Hydroids, 184, 185

Calyptraea, 223, 280

Campanularidse, 183, 184

Capitclla, 330, 332

Carabidae, 476

Carcinus Mcenas, 481, 483

Cardium, 260, 262

" pygmaeum, 262

Carinaria, 240

Caryophyllium, 168, 171 pea, 165, 167

Cecidomyia, 15, 79, 416, 417, 429

Cephalopoda, 20, 40, 41, 102, 108, 109, 135. "5. 240, 242, 244, 250, 252, 253, 270, 271, 272, 274, 279, 282, 287

Cephalothrix galatheae, 202

Ceratosponguc, 146


Cercariae, 207, 208, 209

Cerianthus, 168, 171

Cestodes, 14, 29, 31, 32, 33, 189, 210, 212, 218, 313, 425, 541

Chsetogaster, 342

Chaetopoda, 5, 18, 23, 41, 43, 44 , 54, 67, 209, 215, 270, 275, 307, 312, 317, 318, 319, 320, 326, 334, 33<S, 342, 346, 349, 350, 351, 364. 369. 33, 36, 408, 448, 457, 458, 521, 576,582

ChiXitopteridte, 333

Cha^tosomoidea, 371

Chelifer, 434, 436, 442, 446, 454

Chermes, 15, 429

Chilognatha, 113, 387, 389, 391, 393,

395

Chilopoda, 387, 392, 394 Chilostomata, 292, 297, 298, 304, 305 Chironomus, 15, 378, 401, 402, 415, 416,

429

Chiton, 254, 256, 257, 273 Chordata, 5 Chrysaora, 165 Chthonius, 436 Cicada, 395

Cirripedia, 459, 492, 496,503, 509, 520 Cladocera, 459, 464, 519 Clausilia, 239 Clavella, 520 Clavularia crassa, 167 Cleodora, 241 Clepsine, 73, 346, 347, 349, 351, 352,

353, 354 Clio, 242, 278 Clubione, 436 Clupeidae, 64 Cobitis barbatula, 378 Coccida;, 429 Coccus, 50 Ccelebogyne, 79 Coelenterata, 3, 5, 13, 18, 26, 27, 2S, 35,

74, 93, 94, 126, 148, 170, 178,179, 1 80,

181, 191, 342

Ccenurus cerebralis, 213, 214 Coleochaete, 1 1

Coleoptera, 396, 402, 409, 412, 420, 421, ^5

Collembola, 395, 426 Comatula, 5, 552, 553 Condracanthus, ill, 120, 520 Conochilus volvox, 22 1 Convoluta, 32 Copepoda, 109, 120, 459, 460, 487, 489,

493, 496, 503, 509, 519 Corallium rubrum, 168, 182 Corethra, 422, 423, 424 Crangoninoe, 476 Crnniiuhv, 311 Craniata, 5, 6, 19, 20, 54, 56, 59, 6l, 62,

6 4 , 74, 102

Crinoidea, 35, 36, 544, 550, 568, 576 Criodilus, 321, 324, 328, 341


INDEX.


Crisia, 304 Crocodilia, 63

Crustacea, 5, 6, 18, 51, 66, 102, 109, 120, 458, 4 6 5> 487* 5<>2, 521, 524, 537, 541 Cryptophialus, 499, 509 Crystalloides, 163 Ctenophora, 26, 93, 102, 152, 173, 175,

177, 178, 179, 180, 181, 182 Ctenostomata, 292, 297, 298, 304, 305 Cucullarms elegans, 46, 75, 82, 371, 376 Cucumaria, 546, 556, 574 Cumaceae, 459, 465, 486, 506 Curculio, 421

Cyclas, 259, 260, 261, 265 Cyclops, 376, 377, 418, 489, 503 Cyclostomata, 102, -292, 304 Cymbulia, 241, 242

Cymothoa, 516, 517, 519, 520,524, 528 Cynipidae, 15, 421, 428 Cyphonautes, 297, 301, 304, 306, 308 Cypridina, 500, 502 Cysticercus cellulosce, 214, 217

,, fasciolaris, 216

,, limacis, 213

Daphnia, 79, 464

Dasychone, 331, 336

Decapoda, 66, 248, 459, 465, 469, 504,

511

Dendroccela, 32, 33, 189, 195, 196 Dentalium, 258, 576 Desmacidon, 147 Desor, type of, 196, 197, 201, 202, 204,

212, 424 Diastopora, 304 Dibranchiata, 225, 253 Dicyema, 9, 131, 134, 135, 136 Dimya, 225 Diphyes, 159 Diplozoon, 11, 209, 210 Diporpa, 210 Diptera, 49, 194, 204, 396, 401,402,407,

409, 412, 416, 420, 429 Discina radiata, 317 Discinidse, 311

Discophora, 18, 42, 165, 346, 383 Distomese, 189, 205, 425 Distomum, 31

,, cygnoides, 209

,, globiparum, 207

,, lanceolatum, 205 Dochmius duodenale, 375

,, trigonocephalus, 375 Donacia, 401 Dracunculus, 376, 377

Echinaster fallax, 23

,, Sarsii, 102, 561 Echinodermata, 5, 18, 24, 35, 74, 102,

325, 424, 544, 573, 574, 57 6 > 5 82 Echinoidea, 35, 36, 544, 549, 565, 576 Echinorhyncus, 379, 380


Echinus lividus, 83, 84, 88

Echiurus, 44 , 357, 358

Ectoprocta, 297, 306

Edriophthalmata, 459, 465

Elaphocaris, 473

Elasmobranchii, 23, 56, 59, 61, 62, 64,

67, 105, 106. 107, 108, 109 Enopla, 189, 202 Entoconcha mirabilis, 237 Entomophaga, 421

Entoprocta, 292, 298, 300, 302, 304, 306 Epeira, 436

Ephemera, 395, 409, 420, 422 Ephyra, 186

Epibulia auranliaca, 159, 165 Erichthus, 484, 507 Errantia, 319, 336 Esperia, 147 Estheria, 463, 464 Euaxes, lol, 322, 324, 341, 346,349 Eucharis, 178

,, multicornis, 178

Eucopepoda, 459 Eucope polystyla, 23, 154

Eunice sanguinea, 319

Eupagurus prideauxii, 112, 113, 115, 511, 520

Euphausia, 465, 468, 504, 505, 518, 523

Eurostomata, 176

Eurylepta auriculata, 192

Eurynome, 483

Euspongia, 146, 147

Filaria, 377 Filaridae, 371 Firoloidea, 240 Flagellata, 7, 8 Flustrella, 301, 303 Formica, 396 Fungia, 182, 186 Fusus, 275, 280, 284, 288

Gammarus, 122, 518

,, fluviatilis, 117 ,, locusta, no, 112 Ganoids, 54, 102 Gasteropoda, 39, 41, 98, 225, 226, 229,

230, 232, 233, 240, 258, 260, 261, 270,

272, 275, 279, 283, 324 Gasterosteus, 64, 210 Gastrotricha, 370 Gasterotrochce, 330, 333 Gecarcinus, 465 Geophilus, 392, 393 Gephyrea, 5, 18, 24, 44, 54, 67, 102,

318, 320, 325, 355, 357, 361, 364 Germogen, 134 Geryonia hastata, 156 Geryonidse, 156 Glochidia, 267, 268 Gnathobdellidas, 346, 349 Gordiacea, 94


588


INDEX.


Cimlioidca, 371, 374, 378

nia, 168

Gorgonidce, 181 Gorgoninrc, 181 Gregarinidae, 8 Gryllotalpa, 401, 412, 413 Gunnnineiv, 147, 148 Gymnoblastic Hydroids, 184, 185 Gymnoloemata, 292

Gymnosomata, 225, 240, 241, 242, 270 Gyrodactylus, 210

Halichondria, 147

Ilalisarca, 22, 66, 145

Halistemma, 165

Helicidce, 238

Helioporidae, 182

Helix, 67, 229

Hemiptera, 395, 402, 403, 409, 420, 421

Hessia, 108, 492

Heterakis vermicularis, .374

Heteronereis, 343

Heteropoda, 71, 72, 225, 226, 231, 278

Hexacoralla, 152, 179, 182

Hippopodius gleba, 27, 159

Hirudinea, 74, 84

Hirudo, 350, 351, 352, 353, 354

Holometabola, 420, 422

Holostomum, 205

Holothuria, 19, 25, 35, 549, 558, 576

Holothuroidea, 35, 544, 553, 556

Homarus, 477

Hyaleacea, 273, 275

Hyaleidce, 241

Hydra, 21, 22, 26, 28, 29, 34, 152, 154,

155. 179, 183 Hydractinia, 539 Hydrocoralla, 152, 181, 185 Hydroidea, 152 Hydromedusae, 152, 179, 182, 183, 184,

185, 186, 187 Hydrophilus, 374, 396, 400, 401, 402,

404, 408, 409 Hydrozoa, 14, 19, 26, 27, 67, 102, 152,

155. 165. 179, 1 80, 181, 182, 539 Ilymenoptera, 396, 401, 402, 412, 420,

421, 425

Ichneumon, 396

Inarticulata, 311, 316

Incrmi

Infusoria, 7, 8

Insecta, 5, 15, 18, 19, 25, 46, 395, 396,

4^5, 455. 45 Intoshia gigas, 136 Isidimc, 181 Ixxlyctia, 147 Isopoda, 109, 515, 519, 521, 523, 527

Julus Moneletei, 387, 388, 389 Kochlorine, 499


Lacertilia, 64 Lacinularia, 221, 223

socialis, 75 Lamellibranchiata, 23, 25, 37, 39, 98,

225, 241, 257, 258, 259, 269, 270, 271,

273, 274, 288 Lepadkue, 498

Lepas fascicularis, 224, 493, 494, 495 Lepidoptera, 79, 396, 402, 407, 408, 412,

413, 415, 417, 420, 421, 423, 415, 426.

455

Leptodora, 16, 51 Leptoplana, 74, 189, 192, 193 Lernseopoda, 490, 492, 520 Leucifer, 507

Libellulidae, 402, 403, 409, 420 Limax, 229, 232, 239, 278, 280 Limnadia, 79, 524 Limulus, 534 Lina, 402

Lingulidae, 311, 316 Lithobius, 393 Lobatse, 178

Loligo, 242, 243, 244, 247, 253 Loricata, 507, 514 Lota, 105

Loxosoma, 292, 294, 296, 306, 307 Lucernaria, 185 Lumbricus, 341, 368

,, agricola, 321

,, rubellus, 324

trapczoides, 13, 321, 323 Lumbriconereis, 334 Lymnseus, 82, 98, 226, 227, 232, 238,

281 Lycosa, 436

Macrostomum, 32, 34

Macrura, 476

Malacobdella, 203

Malacodermata, 171

Malacostraca, 66, 459, 462, 465, 504,

505, 506, 511, 523 Mammalia, 56, 58, 59, 64, 66 Marsipobranchii, 59 Mastigopus, 473, 474 Medusoe, 27, 154, 157, i.^s, 16;, 164, 176,

178, 181, 182, 183, 184, 185, 186 Megalopa, 482, 483, 484 Melolontha, 402, 421 Membranipora, 297, 303 Mermithido;, 371 Mesotrochoe, 330 Metachoetoe, 335 Metazoa, Q, 10, 12,67, 86, 125, 135, 14^,

ISO, 179

Millepora, 152, 181

Mitraria, 308, 337

Molgula, 102

Mollusca, 5, 18, 24, 66, 74, 84, 99, 225, 247, 248, 251, 256, 257, 262, 271, 285, 288, 307, 325, 333, 352, 576, 582


INDEX.


589


Monomya, -225 Monostomum capitellum, 205

,, mutabile, 205, 206

Monotrochse, 330 Montacuta, 260, 262 Musca, 396 Muscidae, 420, 423 Myobia, 444, 445 Myrianida, 343 Myriapoda, 22, iir, 113, 387, 394, 395,

4i.3 458 Mynothela, 155 Myrmeleon, 396

Mysis, 120, 469, 472, 486, 504, 509, 525 Mytilus, 260, 261 Myxinoids, 5 Myxispongise, 145 Myzostomea, 369

Nais, 342

Nassa mutabilis, 101, 226, 227, 233, 262,

278, 279, 288, 3^4 Natantia, 487 Natica, 237, 283 Nauplius, 5, 16, 460, 461, 463, 465, 466,

469, 473, 490, 491, 493, 497 Nautilus pompilius, 253, 276 Nebaliadse, 459, 465, 486 Nematoda, 45, 46, 50, 66, 74, 75, 371,

373. 374> 376 Nematogens, 131 Nematoidea, 18, 84, 94, 371, 374 Nematus ventricosus, 13, 427 Nemertea, 94, 189, 196, 202, 204 Nemertines, 30, 31, 33, 93, 136, 195,

202, 328, 333, 424 Nephelis, 82, 346, 349, 350, 351, 352,

354

Nereis, 343

,, diversicolor, 319

,, Dumerilii, 343 Neritina, 229, 237 Neuroptera, 396, 401, 420, 421 Neuroterus ventricularis, 428 Notonecta, 395 Nototrochse, 330, 353 Nudibranchiata, 229, 241

Ocellata, 184

Octocoralla, 152, 179

Octopus, 248

Odontophora, 225, 257, 271

Odontosyllis, 333

Oedogonium, 1 1

Oligochseta, 42, 319, 321, 325, 330, 338,

346, 352 Olynthus, 144 Oniscus murarius, 107, 108, 109, 120,

516, 520, 528 Opercula, 31 Ophiothryx, 36, 549 Ophidia, 64


Ophiuroidea, 136, 544, 553, 562, 565,

576

Ophryotrochoe puerilis, 333 Opisthobranchiata, 225, 232, 237 Ornithodelphia, 109 Orthonectidae, 136

Orthoptera, 395, 414, 420, 421, 425, 426 Ostracoda, 459, 500, 510 Ostrea, 259, 260, 262 Oxyuridse, 46, 373, 374 Oxyurus ambigua, 374 ,, vermicularis, 375

PcEcilopoda, 534 Paguridse, 477 Pakemon, no Palaemonetes, 476 Pakemoninre, 476, 511, 512 Palinurus, 478, 480

Paludina, 66, 227, 229, 235, 270, 278, 280

,, costata, 229

,, vivipara, 226 Pandorina, n Parasita, 489 Pedalion, 221

Pedicellina, 98, 292, 296, 299, 307 Pelagia, 167, 185 Penseinse, 476 Penaeus, no, 113, 465, 469, 473, 474,

504, 518

Pennatulidae, 181 Pentacrinus, 5 Pentastomida, 539, 540 Pentastomum denticulatum, 540, 54!

tsenoicles, 539, 540, 541 Percidae, 64 PerennichaetcE, 335 Peripatus, 5, 386, 411, 412, 413, 542 Petromyzon, 61, 63, 64, 74, 83 Phalangella, 304 Phalangidse, 436 Phallusia, 83

Phascolosoma, 44, 355, 356, 361 Pholcus, 436, 442 Phoronis, 315, 355, 363, 364 Phoxinus laevis, 378 Phryganea, 396, 401, 409 Phylactokemata, 292, 294, 297, 305, 306 Phyllobothrium, 218 Phyllodoce, 329 Phyllopoda, 16, 459, 461, 505 Phyllosoma, 479, 480 Phylloxera, 429 Physophoridoe, 152, 16-2, 164 Pilidium, type of, 196, 200, 201, 202, 704,

424

Pisces, 5 Piscicola, 20, 43 Pisidium, 259, 260, 262, 264 Planaria Neapolitana, 193 Planorbis, 273, 281, 325


590


INDEX.


Platyelminthes, 18, 20, 24, 221, 424 Platygaster, 396, 416, 417, 418, 419 Pleurohrachia, 176, 177, 238 Pneumodermon, 242, 576 Podostomata, 292 Poduridce, 401, 405 Polychaeta, 42, 319, 325, 338 Polydesmus complanatus, 387, 388 Polygordius, 319, 325, 326, 327, 328,

332, 357 386 Polynoe, 42, 331 Polyophthalmus, 328 Polyplacophora, 225, 254, 270, 271, 288 Polystomeas, 189, 205, 209 Polystomum, 209

,, integerrimum, 30, 31, 210

Polytrochne, 330, 333 Polyxenia leucostyla, 158 Polyxenus lagurus, 387 Polyzoa, 98, 303, 305, 306. 30 8 > 3 ! 5. 3^ Porcellana, 483 Porifera, 102, 138, 148 Porthesia, 115 Prorhyncus, 32, 34 Prosobranchiata, 225, 237, 281 Prostomum, 32, 34, 38, 196 Protozoa, 8, 9, lo, n, 86, 135, 149 Protozoaea, 471 Protula Dysteri, 342 Pseudoneuroptera, 426 Pseudoscorpionid;e, 434 Psolinus, 556, 574 Psychidae, 16 Pteraster miliaris, 561 Pteropoda, 98, 225, 226, 229, 230, 232,

240, 258, 270, 272, 279, 283 Pterotrachcea, 71, 229, 240 Pulex, 396

Pulmonata, 39, 225, 232, 238, 281, 282 I'urpura lapillus, 78 Pycnogonida, 538 Pyrosoma, 13, 53, 109

Rana temporaria, 210 Kaspailia, 147 Rcdia, 206, 207, 208, 209 Reniera, 147

Kcptilia, 56, 59, 60, 61, 62, 64, 109 Rhabditis dolichura, 82 Khabdoccela, 32, 33, iSy, ic/> Khnbdopleura, 294, 306 Rhi/occphala, 459, 493, 499, 500 Klii/.ocrinus, 5 klii/.ostoma, 167 Rhomlx>gens, 131, 134 Khynchoncllidaj, 311 Rhyncdbddlkbe, 346 Rotifera, 5, 12, 18, 75, 76, 77, 79, 83, 102, 221, 308, 325

Saccocirrus, 328, 329, 332, 340 Sacculina, 500


Sagartia, 169, 171

Sagitta, 33, 74, 94, 130, 366, 367, 368

Salmonidrc, 64

Salpa, 102

Sarcia, 164

Seaphopoda, 225, 257, 270, 271

Schistocephalus, 2 1 1

Schizopoda, 459, 465, 466

Scolopendra, 392

Scorpio, 120, 43 r, 44 6, 454, 455, 457

Scrobicularia, 38, 39

Scyllarus, 477

Scyphistoma, 179, 185, 186

Sedentaria, 319, 336

Sepia, 20, 40, 41, 242, 243, 244, 245,

247> 2 49> 253 Sergestidce, 473, 507 Serpula, 319. 325, 331 Sertularia, 152, 183, 184 Silicispongia.', 147 Simulia, 401, 415 Siphonophora, 13, 77, 152, 159, 163,

165, 179, 1 80, 182, 185 Sipunculida, 24 Sipunculus, 44 Sirex, 396 Sitaris, 42!

Spathegaster baccarum, 428 Spjo, 4 2 > 33 2 > 333 Spiroptera obtusa, 376 Spirorbis Pagenstecheri, 319

spirillum, 319, 336 Spirula, 252 Spirulirostra, 252 Spongelia, 147 Spongida, 138, 144, 148, 149 Spongilla, 147, 150 Sporocysts, 206, 207, 208, 209 Squilla, 66, 504, 507 Stephanomia pictum, 162, 165 Stomalopoda, 459, 465, 4X4 Stomodoeum, 413 Strongylidrc, 371, 375 Strongylocentrus, 567 Strongysoloma Guerinii, 3<S7, 388, 390 Stylasterictae, 152, r8r Styliolidic, 24! Stylochopsis ponticus, 193 Sycandra, 93, 138, 144, 145, 147, 150

,, raphanus, i^S, 174 Syllis, 343

vivipara, 319 Sympodium coralloidcs, 168

Taeniatoe, 178 Tardigrada, 541 Teoenaria, 436

'I'clcDsti'i, IS, 25, 5^), 59, C>4. 107, io<) I'r].)troch;i.-, 330 Tcndra, 300 'I '(.'nth reds, 396 Tcrcbdla concliilcga, 332, 333, 337


INDEX.


591


Terebella nebulosa, 332, 333 Terebratula, 311, 315 Terebratulina, 311, 315, 316

,, septentrionalis, 315, 316

Teredo, larva of, 262 Tergipes, 232, 238

,, Edwardsii, 238 ,, lacinulatus, 238 Tethya, 147 Tetrabranchiata, 225 Tetranychus telarius, 116 Tetrastemma varicolor, 203 Thalassema, 44, 355, 357 Thalassinidae, 477 Thallophytes, n Thecidium, 311, 312, 315, 316 Thecosomata, 225 Thoracica, 459, 493, 499, 500 Thysanozoon, 192, 193 Thysanura, 395, 408, 425, 458 Tichogonia, 39 Tipula, 396 Tipulidae, 420, 421 Toenia cosnurus, 214

,, echinococcus, 215, 217

solium, 217 Tornaria, 579, 581 Toxopneustes, 22, 24, 35, 85, 88, 89 Tracheata, 385, 426, 432, 44 8, 455, 457,

458, 538, 54i

Trachymedusae, 152, 156, 179, 185 Trematodes, 14, 16, 29, 30, 31, 32, 33,

46, 94, 189, 205, 208, 210, 212, 216


Trichina, 377, 378

Trichinidse, 371

Trichocepha'lus affinis, 374

Trochosphsera aequatorialis, 221

TubiporidcE, 182

Tubularia, 34, 38, 152, 154, 158

Tubularidse, 29, 179, 183

Tunicata, 5, I 4 , 53

Turbellaria, 5, 30, 31, 33, 74, 98, 102,

136, 179, 189, 193, 333 Tyroglyphus, 445

Unio, 37, 38, 39, 100, 101, 259, 260,265, 266, 445

Vaginulus luzonicus, 229

Vermes, 5, 74, 102, 223, 324, 352

Verongia rosea, 146

Vertebrata, 14, 18, 19, 24, 59, 64, 83,

272, 349. 397' 4^6 Vesiculata, 184 Vitrina, 229 Vorticella, 8, 9, 10

Wilsia, 164 Xiphoteuthis, 252

Zoantharia, 152, 168, 169 Zooea, 465, 468, 471, 474, 482, 483, 484, 486, 504


BIBLIOGRAPHY.


THE OVUM.

General Works.

(1) } Ed. van Beneden. "Recherches sur la composition et la signification de ,A T m ' cour ' d ' l Acad " r y- des Sci <<* de Belgique, Vol. xxxiv. 1870.

/ '%, R- Leuckart. Artikel "Zeugung," R. WagMsfs Handworterbtek d. Physio logte, Vol. iv. 1853.

(3 ^ Fr ' L/ydig- , " Die Dotterfurchung nach ihrem Vorkommen in d. Thierwelt u. n. ihrer Bedeutung." Oken. Isis, 1848.

(4) Ludwig. "Ueber d. Eibildung im Thierreiche." Arbeiten a. d. zool.-zoot Institiit. Wiirzburg, Vol. I. rSy^.

(5) AllenThomson. Article ' ' Ovum " in Todd's Cyclopedia of Anatomy and Physiology, Vol. v. 1859.

(6) W. Waldeyer. Eierstock u. EL Leipzig, 1870.

THE OVUM OF CCELENTERATA.

(7) Ed. van Beneden. "De la distinction originelle d. testicule et de 1'ovaire." Bull. Acad. roy. Belgique, f serie, Vol. xxxvu. 1874.

(8) R. and O. Hertwig. Der Organismus d. Medusen. Jena, 1878.

(9) N. Kleinenberg. Hydra. Leipzig, 1872.

THE OVUM OF PLATYELMINTHES.

(10) P. Hallez. Contributions a fHistoire naturelle des Turbellarih. Lille, 1879.

(11) S. MaxSchultze. Beitrdge z. Naturgeschichte d. Turbellarien. Greifswald, 1851.

(12) C. Th. von Siebold. ' ' Helminthologische Beitrage." Miiller's Archiv, 1836.

(13) C. Th. von Siebold. Lehrbuch d. vergleich. Anat.d. wirbellosen Thiere. Berlin, 1848.

(14) E. Zeller. " Weitere Beitrage z. Kenntniss d. Polystomen." Zeit. f. wiss. ZooL, Bd. xxvu. 1876.

[Vide also Ed. van Beneden (No. i).]

THE OVUM OF ECHINODERMATA.

(15) C. K. Hoffmann. " Zur Anatomic d. Echiniden u. Spatangen." Niederllindisch. Archiv f. Zoologie, Vol. I. 1871.

(16) C. K. Hoffmann. " Zur Anatomic d. Asteriden. Niederldndisch. Ardiiv /. Zoologie, Vol. n. 1873.

(17) H. Ludwig. "Beitrage zur Anat. d. Crinoiden." Zeil. f. wiss. Zool., Vol. xxvin. 1877.

(18) Job. Miiller. "Ueber d. Canal in d. Eiern d. Holothurien." Miiller's Archiv, 1854.

(19) C. Semper. Holothurien. Leipzig, 1868.

(20) E. Selenka. Befruchtung d. Eies v. Toxopneustes variegalits, 1878.

[Vide also Ludwig (No. 4), etc.]

1 A very complete and critical account of the literature is contained in this paper. B. II. a


BIBLIOGRAPHY.


THE OVUM OF MOLLUSC A. Lamellibranchiata.

(21) II. Lacaze-Duthiers. " Organes genitaux des Acephales Lamellibranches." Ann. Set. Nat., 4 mc serie, Vol. 1 1. 1854.

(22) W. F lemming. " Ueb. d. er. Entwick. am Ei d. Teichmuschel." Archiv f. mikr. Anat., Vol. x. 1874.

(23) W. Flamming. "Studien lib. d. Entwick. d. Najaden." Sitz. d. t: Akad. Wiss. men, Vol. LXXI. 1875.

(24) Th. von Hassling. " Einige Bemerkungen, etc." Zeit. f. wiss. ZooL, Bd. v. 1854.

(25) H. von Jhering. "Zur Kenntniss d. Eibildung bei d. Muscheln." Zeit. f. wiss. ZooL, Vol. xxix. 1877.

(26) Keber. De Introihi Spermatozoorum in ovula, etc. Konigsberg, 1853.

(27) Fr. Leydig. " Kleinere Mittheilung etc." Miiller's Archiv, 1854.

Gasteropoda.

(28) C. Semper. "Beitrage z. Anat. u. Physiol. d. Pulmonaten." Zeit. f. wiss. ZooL, Vol. vni. 1857.

(29) H. Eisig. " Beitrage z. Anat. u. Entwick. d. Pulmonaten." Zeit.f. wiss. ZooL, Vol. xix. 1869.

(30) Fr. Leydig. " Ueb. Paludina vivipara." Zeit.f. wiss. ZooL, Vol. u. 1850.

Cephalopoda.

(31) Al. Kolliker. Entwicklungsgeschichte d. Cephalopoden. Zurich, 1844.

(32) E. R. Lankester. "On the Developmental History of the Mollusca." Phil. Trans., 1875.

THE OVUM OF THE CHJETOPODA.

(33) Ed. Claparede. " Les Annelides Chaetopodes d. Golfe de Naples." Mem.d. 1. Soctit. phys. eld 1 hist. nat. de Geneve, 1868 9 and 1870.

(34) E. Ehlers. Die Borstcnwiirmer nach system, und anat. Untersuchungen. Leipzig, 186468.

(35) E. Selenka. " Das Gefass-System d. Aphrodite aculeata." Niedcrldndisches Archiv f. ZooL, Vol. n. 1873.

THE OVUM OF DISCOPHORA.

(36) H. Dorner. " Ueber d. Gattung Branchiobdella." Zeit.f. wiss. ZooL, Vol. xv. 1865.

(37) R. Leuckart. Die menschlichen Parasiten.

(38) Fr. Leydig. "Zur Anatomie v. Piscicola eeometrica, etc." Zeit. f. wiss. ZooL, Vol. I. 1849.

(30) C. O. Whitman. "Embryology of Clepsine." Quart. 7. of Alter. Sci., Vol. xvin. 1878.

THE OVUM OF GEPHYREA.

(40) Keferstein u. Ehlers. Zoologische Beitrage. Leipzig, 1861.

(41) C. Semper. Holothurien, 1868, p. 145.

(42) J. W. Spengel. " Beitrage z. Kenntniss d Gephyreen." Beitriigc a. d. zool. Stationz. Neapcl, Vol. I. 1879.

(43) J. W. Spengel. " Anatomische Mittheilungen lib. Gephyreen." Tagcbl. d. Naturf. Vers. Munchen, 1877.

THE OVUM OF NEMATODA.

(44) Ed. Claparede. De la formation ct de la fccondaiiou dcs- n-uf.\ chcz Ics I'crs Ntmatodcs. (ienevc, 1859.

(J- r )) K. I. (.-nek art. Hif nirnsf/i lichen Paras! ten.


BIBLIOGRAPHY. jjj


d.Nematoden."

^' Nels0n * " On the reproduction of Ascaris mystax, etc." Phil. (48) A.Schneider. Monographie d.' Nematoden. Berlin, 1866. THE OVUM OF INSECT A.


Sm ' T? r u n d V Ueb ,?'* a5 Ei u ' seine Bildungsstdtte. Leipzig, 1 878. (50) T. H. Huxley. " On the agamic reproduction and morphology of Aphis. Ltnnean Trans., Vol. xxn. 1858. Vide also Manual of Invertebrate* Animals, 1877.

1 * ^ ^ ^ *


(51) bei den *,++,*

/-a\ ? r ',k ey< MS' Der Eierstock u. die Samentasche d. Insecten. Dresden, 1866. tSl ~ ub . bock - " The ov a and pseudova of Insects." Phil. Trans. 1850. (o4) Stem. Die weiblichen Geschlcchtsorgane d. Ktifer. Berlin, 1847. [Conf. also Glaus, Landois, Weismann, Ludwig (No. 4).]

THE OVUM OF ARANEINA.

(55) Victor Cams. " Ueb. d. Entwick. d. Spinneneies." Zeit. f. wiss. Zool. t Vol. ii. 1850.

(56) v. Wittich. "Die Entstehung d. Arachnideneies im Eierstock, etc." Miiller s Archiv, 1849.

[Conf. Leydig, Balbiani, Ludwig (No. 4), etc.]

THE OVUM OF CRUSTACEA.

(57) Aug. Weismann. "Ueb. d. Bildung von Wintereiern bei Leptodora hyalina." Zeit.f. wiss.ZooL, Vol. xxvn. 1876.

[For general literature vide Ludwig, No. 4, and Ed. van Beneden, No. i.]

THE OVUM OF CHORD ATA.

Urochorda (Tunicata).

(58) A. Kowalevsky. " Weitere Studien ii. d. Entwicklung d. Ascidien." Archiv f. micr. Anat., Vol. VII. 1871.

(59) A. Kowalevsky. "Ueber Entwicklungsgeschichte d. Pyrosoma." Arch.f. micr. Anat., Vol. xi. 1875.

(60) Kupffer. " Stammverwandtschaft zwischen Ascidien u. Wirbelthieren." Arch. f. micr. Anat., Vol. VI. 1870.

(61) Giard. " Etudes critiques des travaux, etc. " Archives Zool. experiment., Vol. I. 1872.

(62) C. Semper. " Ueber die Entstehung, etc." Arbeiten a. d. zool.-zoot. Institut Wiirzburg, Bd. II. 1875.

Cephalochorda.

(63) P. Langerhans. "Z. Anatomic d. Amphioxus lanceolatus," pp. 330 3. Archiv f. mikr. Anat., Vol. xil. 1876.

Craniata.

(64) F. M. Balfour. "On the structure and development of the Vertebrate Ovary." Quart. J. of Micr. Science, Vol. xvm. 1878.

(65) Th. Eimer. " Untersuchungen ii. d. Eier d. Reptilien." Arckiv f. mikr. Anat., Vol. vni. 1872.

(66) Pfliiger. Die Eierstbcke d. Sdugethiere u. d. Menschen. Leipzig, 1863.

(67) J. Foulis. " On the development of the ova and structure of the ovary in Man and other Mammalia." Quart. J. of Micr. Science, Vol. XVI. 1876.

(68) J. Foulis. " The development of the ova, etc." Journal of Anat. and Phys., Vol. xni. 18789.

a 2


IV BIBLIOGRAPHY.


(69) C. Gegenbaur. " Ueb. d. Bau u. d. Entwicklung d. Wirbelthiereier mit partieller Dottertheilung." Muller's Archiv, 1861.

(70) Alex. Gotte. Entwicklungsgeschichte d. Unke. Leipzig, 1875.

(71) W. His. Untersuchungen iib. d. Ei u. d. Eientwicklung bei Knochenfischcn. Leipzig, 1873.

(72) A. Kolliker. Entwicklungsgeschichte d. Menschen u. hoherer Thicre, Leipzig, 1878.

(73) J. Miiller. " Ueber d. zahlreichen Porenkanale in d. Eikapsel d. Fische." Muller's Archiv, 1854.

(74) W. H. Ransom. " On the impregnation of the ovum in the Stickleback." Pro. K. Society, Vol. vn. 1854.

(75) C. Semper. " Das Urogenitalsystem d. Plagiostomen etc." Arbeiten a. d. zool.-zoot. Instit. Wiirzburg, Vol. II. 1875.

[Cf. Ludwig, No. 4, Ed. van Beneden, No. i, Waldeyer, No. 6, etc.]


MATURATION AND IMPREGNATION OF THE OVUM.

(76) Auerbach. Organologische Studien, Heft 2. Breslau, 1874.

(77) Bambeke. " Recherches s. Embryologie des Batraciens." Bull, de royale de Belgique, 2me ser., T. LXI. 1876.

(78) E. van Beneden. " La Maturation de 1'CEufdes Mammiferes." Bull, de fAcad. royale de Belgique, 2me ser., T. XL. No. 12, 1875.

(79) Id em. " Contributions a 1'Histoire de la Vesicule Germinative, &c." Bull, de fAcad. royale de Belgique, sme ser., T. XLI. No. i, 1876.

(80) O. Biitschli. Eizelle, Zelltheilung, und Conjugation der Infusorien. Frankfurt, 1876.

(81) F. M. Balfour. " On the Phenomena accompanying the Maturation and Impregnation of the Ovum." Quart. J. of Micros. Science, Vol. xvm. 1878.

(82) Calberla. " Befruchtungsvorgang beim Ei von Petromyzon Planeri.*' Zeit. f. iviss. Zool., Vol. xxx.

(83) W. Flemming. "Studien in d. Entwickelungsgeschichte der Najaden." Sitz. d. k. Akad. Wiett, B. LXXI. 1875.

(84) H. Fol. "Die erste Entwickelung des Geryonideneies. " Jenaische Zeitschrift, Vol. vn. 1873.

(85) Idem. " Sur le Developpement des Pte"ropodes." Archives de Zoologic Experimental et Gtnerale, Vol. iv. and v. 1875 6.

(86) Idem. " Sur le Commencement de 1'Henog^nie." Archives des Sciences Physiques et Naturelles. Geneve, 1877.

(87) Idem. Recherches s. I. Ftcondation etl. comrnen. d. rHcnogcnic. Geneve, 1879.

(88) R. Greeff. " Ueb. d. Bau u. d. Entwickelung d. Echinodermen." Sitzun. der Gesellschaft z. Befonlerung d. gesammten Naturwiss. z. Marburg, No. 5, 1876.

(89) Oscar Hertwig. " Beit. z. Kenntniss d. Bildung, &c., d. thier. Eies." Morphologisches Jahrbuch, Vol. I. 1876.

(90) Idem. Ibid. Morphologisches Jahrlntch, Vol. ill. Heft i, 1877.

(91) Idem. " Weitere Beitrage, &c." Morphologisches Jahrbuch, Vol. in. 1877. Heft 3.

(92) Idem. "Beit. z. Kenntniss, &c." Morphologisches Jahrbuch, Vol. iv. Heft i and 2. 1878.

(93) N. Kleinenberg. Hydra. Leipzig, 1872.

(94) C. Kupffer u. B. Benecke. Der Vorgang d. llcfnichtinig am Eie d. Neunaugen. Konigsberg, 1878.

(95) J. Oellacher. "Beitrage zur Geschichte des Keimblaschens im Wirbelthicreie." Archiv f. micr. Anat., Bd. VIII. 1872.

(%) W. Salensky. " Befruchtung u. P^urchung d. Sterlets-Eies." Zoologischer Anzeigcr, No. 11, 1878.

(97) E. Selenka. Befruchtung des Eies von Toxopncustcs variegatus. Leipzig, 1878.

fl Strasburger. Ucber Zclllnldu n- n. /.clltln ////;/;. Ji-na, 1876.

Idem. Utber Befrvehtung u. Zdlthdhing. Jena, 1X78.

(HiO) C. (). \V hi tin.in. "Tlic- Kniliryology of Clepsine." Quart. J. of A/i<r. Science, Vol. xvm. 1878.


BIBLIOGRAPHY.


DIVISION OF NUCLEUS.

(101) W. Flamming. "Beitrage z. Kenntniss d. Xclle u. ihrcr Lcbun.scrschcinungen." Archiv f. mikr. Anat., Vol. xvi. 1878.

(102) E. Klein. "Observations on the glandular epithelium and division of nuclei in the skin of the Newt." Quart, y. of Micr. Science, VoL XIX. 1879.

(103) Peremeschko. "Ueber d. Theilung d. thierischen Zellen." Archiv f. mikr. Anat., Vol. xvi. 1878.

(104) E. Strasburger. "Ueber ein z. Demonstration geeignetes ZclltheilungsObject." Sitz. d. Jenaischen Gesell.f. Med. u. Naturwiss., July 18, 1879.

SEGMENTATION.

(105) E. Haeckel. "Die Gastrula u. Eifurchung." Jenaische Ztitschrift, Vol. ix. 1877.

(106) Fr. Leydig. "Die Dotterfurchung nach ihrem Vorkommen in d. Thierwelt u. n. ihrer Bedeutung." Oken. /sis, 1848.

GENERAL WORKS ON EMBRYOLOGY.

(107) K. E. von Baer. " Ueb. Entwicklungsgeschichte d. Thiere." Konigsberg, 182837.

(108) C. Glaus. Grundziige d. Zoologie. Marburg und Leipzig, 1879.

(109) C. Gegenbaur. Grundriss d. vergleichenden Anatomie. Leipzig, 1878. Vide also Translation. Elements of Comparative Anatomy. Macmillan and Co., 1878.

(110) E. Haeckel. Studien z. Gastrcea-Theorie. Jena, 1877, and also Jenaische Zeitschrift, Vols. vni. and ix.

(111) E. Haeckel. Schopfungsgeschichte. Leipzig. Vide also Translation. The History of Creation. King and Co., London, 1876.

(112) E. Haeckel. Anthropogenie. Leipzig. Vide also Translation. Anthropogeny (Translation). Kegan Paul and Co., London, 1878.

(113) Th. H.Huxley. The Anatomy of Invertebrated Animals. Churchill, 1877.

(114) E. R. Lankester. "Notes on Embryology and Classification." Quart. J. of Micr. Science, Vol. xvi I. 1877.

(115) A. S. P. Packard. Life Histories of Animals, including Man, or Outlines of Comparative Embryology. Holt and Co., New York, 1876.

(116) H. Rathke. Abhandlungen z. Bildung- und Entwicklungsgesch. d. Menschen u. d. Thiere. Leipzig, 1833.

DICYEMID.E.

(117) E van Beneden. "Recherches sur les Dicyemides." Bull. d. FAcadtmie roy. de Belgique, f ser. T. XLI. No. 6 and T. XLII. No. 7, 1876. Vide this paper for a full account of the literature.

(118) A. K 611 ike r. Ueber Dicyema paradoxum den Schmarotzer der Venenanhiinge der Cephalopoden. ,

(119) Aug. Krohn. "Ueb. d. Vorkommen von Entozoen, etc. Fronep

Notizen, vn. 1839.

ORTHONECTID^E.

(120) A If. Giard. "Les Orthonectida classe nouv. d. Phylum des Vers." journal de tAnat. et de la Physiol., Vol. XV. 1879.

(121) El. Metschnikoff. "Zur Naturgeschichte d. OrthonecUdae." Zoologi scher Anzeiger, No. 40 43 l8 79 PORIFERA. '(122) C Barrois. " Embryologie de quelques eponges de la Manche. " An ""$) & &ZS^^'<t*>* SP"6es." A~* ^ M g . cf Nat. Hist., 4th series, Vol. xiv. 1874.




vi BIBLIOGRAPHY.


(124) Ganin 1 . " Zur Entwicklung d. Spongilla fluviatilis." Zoologischer Anzeigtr, Vol. i. No. 9, 1878.

(125) Robert Grant. "Observations and Experiments on the Structure and Functions of the Sponge." Edinburgh Phil. jf., Vol. xm. and XIV., 1825, 1816.

(126) E. Haeckel. Die Kalkschwamme, 1872.

(127) E. Haeckel. Studien zur Gastraa- Theorie. Jena, 1877.

(128) C. Keller. Unterstichungen iiber Anatomic und Entwicklungsgeschichte einiger Spongien. Basel, 1876.

(129) C. Keller. "Studien lib. Organisation u. Entwick. d. Chalineen." Zeit. f. wiss. Zoo/., Bd. xxvin. 1879.

(130) LieberkUhn. "Beitr. z. Entwick. d. Spongillen." Muller's Archiv, 1856.

(131) LieberkUhn. "Neue Beitrage zur Anatomie der Spongien." Miiller's Archiv, 1859.

(132) El. Metschnikoff. " Zur Entwicklungsgeschichte der Kalkschwamme. " Zeit.f. wiss. Zool., Bd. xxiv. 1874.

(133) El. Metschnikoff. "Beitrage zur Morphologic der Spongien." Zeit. f. wiss. Zool., Bd. xxvii. 1876.

(134) El. Metschnikoff. " Spongeologische Studien." Zeit. f. wiss. Zool., Bd. xxxn. 1879.

(135) Miklucho Maklay. "Beitrage zur Kenntniss der Spongien." Jenaische Zeitschrift, Bd. iv. 1868.

(136) O. Schmidt. "Zur Orientirung iiber die Entwicklung der Schwamme." Zeit.f. wiss. Zool., Bd. xxv. 1875.

(137) O. Schmidt. "Nochmals die Gastrula der Kalkschwamme." Archiv fur mikrosk. Anat., Bd. XII. 1876.

(138) O. Schmidt. "Das Larvenstadium von Ascetta primordialis und Asc. clathrus." Archiv fur mikrosk. Anatomie, Bd. xiv. 1877.

(139) F. E. Schulze. "Ueber den Bau und die Entwicklung von Sycandra raphanus." Zeit.f. wiss. Zool., Bd. xxv. 1875.

(140) F. E. Schulze. "Zur Entwicklungsgeschichte von Sycandra." Zeit. f. wiss. Zool., Bd. XXVII. 1876.

(141) F. E. S chulze. " Untersuchung Ub. d. Bau, etc. Die Gattung Halisarca." Zeit.f. wiss. Zoo/., Bd. xxvin. 1877.

(142) F. E. Schulze. "Untersuchungen iib. d. Bau, etc. Die Metamorphose von Sycandra raphanus." Zeit.f. wiss. Zool., Bd. xxxi. 1878.

(143) F. E. Schulze. "Untersuchungen u. d. Bau, etc. Die Familie Aplysinidae." Zeit.f. wiss. Zool., Bd. xxx. 1878.

(144) F. E. Schulze. "Untersuchungen u. d. Bau, etc. Die Gattung Spongelia." Zeit.f. wiss. Zool., Bd. xxxn. 1878.

CCELENTERATA. General.

(145) Alex. Agassi z. Illustrated Catalogue of the Museum of Comparative Anatomy at Harvard College, No. II. American Acalephac. Cambridge, U. S., 1865.

(140) O. and R. Hertwig. Der Organismus d. Medusa: u, seine Stellung z. Keimblattertheorie. Jena, 1878.

(147) A. Kowalevsky. "Untersuchungen lib. d. Entwicklung d. Coelenteraten." Nachrichten d. kaiser. Gcsell. d. Freunde d. Nattirerkenntniss d. Antliropologie u. Ethnographie. Moskau, 1873. (Russian). For abstract vide Jahresberichtc d. Anat. u. Phys. (Hoffman u. Schwalbe), 1873.

Hydrozoa.

(148) L. A gas si z. Contributions to the Natural History of the United States of America. Boston, 1862. Vol. IV.

(149) G. J. Allman. A Monograph of the Gymnoblastic or Tubularian Hydrotds. Ray Society, 1871-2.

1 There is a Russian paper by the same author, containing a full account, with clear illustrations, of his observations.


BIBLIOGRAPHY, vii


(150) G. J. All man. "On the structure and development of Myriothela." Phil. Trans., Vol. CLXV. p. 2.

(Iff), P - J- van Beneden. "Mem. sur les Campanulaires de la Cote d'Ostende consideres sous le rapport physiologique, embryogenique, et zoologique." Nouv. Mini. de PAcad. de Brux., Tom. xvn. 1844.

(^ 2 ) p - J- van Beneden. "Recherches sur 1'Embryogenie des Tubulaires et 1 histoire naturelle des differents genres de cette famille qui habitent la Cote d'Ostende." Nouv. Mem. de P Acad. de Brux., Tom. xvii. 1844.

(153) C. Claus. "Polypen u. Quallen d. Adria." Denk. d. math.-naturwiss. Classe d. k. k. Akad. d. Wiss. Wien, Vol. xxxvin. 1877.

(154) J. G. Dal yell. Rare and Remarkable Animals of Scotland. London, 1847.

(* 55 ) , H - Fo1 - " Die er ste Entwicklung d. Geryonideneies." J 'enaische Zeit schrift, Vol. vn. 1873.

(156) Carl Gegenbaur. Zur Lehre vom Generationswechsel und der Fortpfianzung bei Medusen und Polypen. Wiirzburg, 1854.

(157) Thomas Hincks. "On the development of the Hydroid Polypes, Clavatella and Stauridia ; with remarks on the relation between the Polype and the Medusoid, and between the Polype and the Medusa." Brit. Assoc. Rep., 1861.

(158) E. Haeckel. Zur Entwicklungsgeschichte d. Siphonophoren. Utrecht, 1869.

(159) Th. H. Huxley. Oceanic Hydrozoa. Ray Society, 1858.

(160) Geo. Johnston. A History of British Zoophytes. Edin. 1838. 2nd Edition, 1847.

(161) N. Kleinenberg. Hydra, eine anatomisch-entwicklungsgeschichtliche Untersuchung. Leipzig, 1872.

(162) El. Metschnikoff. "Ueber die Entwicklung einiger Ccelenteraten." Bull, de FAcad. de St Petersbourg, XV. 1870.

(163) El. Metschnikoff. "Studien liber Entwicklungsgeschichte d. Medusen u. Siphonophoren." Zeit.f. wiss. ZooL, Bd. xxiv. 1874.

(164) H. N. Moseley. "On the structure of the Sty lasteridse." Phil. Trans.,

(165) F. E. Schulze. Ueber den Bau und die Entwicklung von Cordylophora lacustris. Leipzig, 1871.

Actinozoa.

(166) Al. Agassiz. "Arachnitis (Edwarsia) brachiolata." Proc. Boston Nat. Hist. Society, 1860.

(167) Koch. "Das Skelet d. Alcyonarien." Morpholog. Jahrbuch, Bd. iv. 1878.

(168) A. Kowalevsky. "Z. Entwicklung d. Alcyoniden, Sympodium coralloides und Clavularia crassa." Zoologischer Anzeiger, No. 38, 1879.

(169) H. Lacaze Duthiers. Histoire nat.du Cor ail. Paris, 1864.

(170) H. Lacaze Duthiers. " Developpement des Coralliaires." Archives de Zoologie experimental et generate, Vol. I. 1872 and Vol. u. 1873.

(171) C. Semper. " Ueber Generationswechsel bei Steinkorallen etc." Zeit. f. wiss. ZooL, Bd. xxii. 1872.

Ctenophora.

(172) Alex. Agassiz. "Embryology of the Ctenophorae." Mem. of the Anur. Acad. of Arts and Sciences, Vol. X. No. 1 1 1. 1874.

(173) G. J. All man. "Contributions to our knowledge of the structure and development of the Beroidse." Proc. Roy. Soc. Edinburgh, Vol. IV. 1862.

(174) C. Chun. "Das Nervensystem u. die Musculatur d. Rippenquallen." Abhand. d. Senkenberg. Gesellsch., B. XI. 1879.

(175) C. Claus. "Bemerkungen u. Ctenophoren u. Medusen." Zeit. f. wiss. ZooL, xiv. 1864.

(176) H. Fol. Ein Beitrag z. Anat. u. Entwickl. einiger Rippenquallen. 1869.

(177) C. Gegenbaur. "Studien u. Organis. u. System d. Ctenophoren." Archiv f. Naturgesch., xxii. 1856.

(178) A. Kowalevsky. " Entwicklungsgeschichte d. Rippenquallen. " Mtm. Acad. St Petersbourg, vii. serie, Tom. x. No. 4. 1866.


Vlii BIBLIOGRAPHY.


(179) J. Price. "Embryology of Ciliogrades." Proceed, of British Assoc., 1846.

(180) C. Semper. "Entwicklung d. Eucharis multicornis." Zeit. f. wtss. Zool., Vol. IX. 1858.

PLATYELMINTHES. Turbellaria.

(181) Alex. Agassiz. "On the young stages of a few Annelids" (Planaria angitlata). Annals Lyceum Nat. Hist, of Neiv York, Vol. vin. 1866.

(182) Dalyell. "Powers of the Creator."

(183) C. Girard. "Embryonic development of Planocera elliptica." J our. of Acad. of Nat. Set., Philadelphia. New Series, Vol. II. 1854.

(184) Alex. Gotte. "Zur Entwicklungsgeschichte d. Seeplanarien." Zoologischer Anzeiger, No. 4, 1878.

(185) P. Halle z. Contributions a Thistoire naturelle des Turbellarits. Thesis a la facult^ des Sciences p. le grade d. Docteur es-sciences naturelles. Lille, 1879.

(186) Knappert. "Bijdragen tot de Ontwikkelings-Geschiedenis der Zoetwater-Planarien." Provinciaal Ulrechtsch Genootschap van Kunsten en Wetenschappen. Utrecht, 1865.

(187) W. Keferstein. " Beitrage z. Anat. u. Entwick. ein. Seeplanarien von St. Malo." Abh. d. konig. Gesell. d. Wiss. zu Gottingcn. Bd. XI v. 1868.

(188) El. Metschnikoff. " Untersuchungen lib. d. Entwicklung d. Planarien." Notizen d. neurussischen Gesellschaft d. Naturforscher. Odessa, Bd. V. 1877. Vide Hoffman and Schwalbe's Bericht for 1878.

(189) H. N. Moseley. "On Stylochus pelagicus and a new species of pelagic Planarian, with notes on other pelagic species, on the larval forms of Thysanozoon, etc." Quart. Journ. of Micr. Science, Vol. xvn. 1877.

(190) J. Miiller. "Ueber eine eigenthiimliche Wurmlarva a. d. Classe d. Turbellarien, etc." Miiller's Archiv f. Anat. u. Phys. 1850.

(191) J. Miiller. "Ueber verschiedene Formen von Seethieren." Miiller's Archiv f. Anat. und Phys. 1854.

Nemertea.

(192) J. Barrois. " L'Embryologie des Nemertes." An. Sci. Nat., Vol. VI. 1877.

(193) O. BUtschli. Archiv f. Naturgeschichte, 1873.

(194) A. Krohn. "Ueb. Pilidium u. Actinotrocha." Miiller's Archiv, 1 858.

(195) E. Desor. "Embryology of Nemertes." Proceedings of the Boston Nat. History Society, Vol. VI. 1848.

(196) G. Dieck. "Entwicklungsgeschichte d. Nemertinen." Jenaische Zeitschrift, Vol. vin. 1874.

(197) C. Gegenbaur. "Bemerkungen lib. Pilidium gyrans, etc." Zeitschrift furwiss. Zool., Bd. v. 1854.

(198) C. K. Hoffman. "Entwicklungsgeschichte von Tetrastemma tricolor." Niederldndisches Archiv, Vol. ill. 1876, 1877.

(199) C. K. Hoffman. "Zur Anatomie und Ontogenie von Malacobdella." Niederldndisches Archiv, Vol. IV. 1877.

(200) W. C. M c Intosh. British Annelids. The Nemerteans. Ray Society, J873-4.

(201) Leuckart u. Pagenstecher. "Untersuchungen lib. niedere Seethiere." Miiller's Archiv, 1858.

(202) E. Metschnikoff. "Studien lib. die Entwicklung d. Echinodermen u. Nemertinen." Mhn. Acad. imp. Pttersbourg, vn. Ser., Tom. xiv. No. 8, 1869.

Trematoda.

(203) T. S. Cobbold. Kntozoa. Groombridge and Son, 1864.

(204) T. S. Cobbold. Parasites; a Treatise on the Entozoa, etc. Churchill, 1879.

(205) F i 1 i p p i. " Mem. p. servir a 1'histoire geneHique des Tre"matodes." Ann. Scien. Nat., 4th Series, Vol. II. 1854, and Mem. Accad. Torino, 1855-1859.


BIBLIOGRAPHY. ix


206) R. Leuckart. Die menschlichen Parasilen, Vol. I. 1863, p. 485 ct seq.

207) H. A. Pagenstecher. Trematodtn u. Trematodenlarven. Heidelberg,

1857.

(208) C. Th. von Siebold. Lehrbuch d. vergleich. Anat. wirbelloser Thicre. Berlin, 1848.

( 209 ) J- J- S. Steenstrup. Generationswechsel. 1842.

(210) R. v. Willemoes-Suhm. "Zur Naturgeschichte d. Polystomuiu intcgerrimum, etc." Zeit.f. wiss. Zool., Vol. xxn. 1872.

(211) R. v. Willemoes-Suhm. Helminthologische Notizcn III." Zeit. f. wiss. Zool., Vol. xxiii. 1873. Vide this paper for a summary of known observations and literature.

(212) G. R. Wagener. Beitrdge zur Entwicklungsgeschichte d. Eingeweidewiirmer. Haarlem, 1855.

(213) G. R. W age n e r. " Helminthologische Bemerkungen, etc." Zeit. f. wiss. Zool., Vol. ix. 1850.

(214) G. R. Wagener. "Ueb. Gyrodactylus elegans." Archiv f. Anat. u. Phys. 1860.

(215) E. Zeller. " Untersuchungen ub. d. Entwicklung d. Diplozoon paradoxum." Zeit.f. wiss. Zool., Vol. xxn. 1872.

(216) E. Zeller. "Untersuchungen u. d. Entwick. u. Bau d. Polystomum integerrimum." Zeit.f. wiss. Zool., Vol. xxn. 1872.

(217) E. Zeller. "Weitere Beitrage z. Kenntniss d. Polystomen." Zeit.f. wiss. Zool., Vol. xxvn. 1876.

Cestoda.

(218) Ed. van Beneden. "Recherches sur la composition et la signification d. 1'oeuf." Mem. cour. Acad. roy. Belgique. Vol. xxxiv. 1868.

(219) P. J. van Beneden. "Les vers Cestoi'des consideres sous le rapport physiologique embryogenique, etc." Bull. Acad. Scien. Bruxelles. Vol. xvn. 1850.

(220) T. S. Cobbold. Entozoa. Groombridge and Son, 1864.

(221) T. S. Cobbold. Parasites; a treatise on the Entozoa, etc. Churchill, 1879.

(222) Th. H. Huxley. "On the Anatomy and Development of Echinococcus veterinorum." Proc. Zool. Soc. Vol. xx. 1852.

(223) J. Knoch. "Die Naturgesch. d. breiten Bandwiirmer." Mem. Acad. Imp. Petersbourg, Vol. v. Ser. 7, 1863.

(224) F. Kiichenmeister. "Ueber d. Umwandlung d. Finnen Cysticerci in Bandwiirmer (Tsenien)." Prag. Vierteljahrsschr. 1852.

(225) F. Kiichenmeister. "Experimente iib. d. Entstehung d. Cestoden. 2 Stufe zunachst d. Ccenurus cerebralis." Giinsburg, Zeitsch. klin. Med. iv. 1853.

(226) R. Leuckart. Die menschlichen Parasiten, Vol. I. Leipzig, 1863. Vide also additions at the end of the ist and 2nd volume.

(227) R. Leuckart. "Archigetes Sieboldii, eine geschlechtsreife Cestodenamme." Zeit.f. wiss. Zool., Vol. xxx. Supplement, 1878.

(228) El. Metschnikoff. "Observations sur le developpement de quelques animaux (Bothriocephalus proboscideus). " Bull. Acad. Imp. St Petersbourg, Vol.

(229) 'w. Salensky. "Ueb. d. Bau u. d. Entwicklungsgeschichte d. Amphilina." Zeit.f. wiss. Zool., Vol. xxiv. 1874.

(230) Von Siebold. Burdach's Physiologie.

(231) R. von Willemoes-Suhm. "Helminthologische Notizen." Zfit. /. wiss. Zool., Vol. xix. xx. xxn. 1869, 70 and 73.

ROTIFERA.

(232) F. Cohn. "Ueb. d. Fortpflanzung von Raderthiere." Zeit.f. wiss.

^(233) F. Cohn. "Bemerkungen u. Raderthiere." Zeit.f. wiss. Zool., Vol. IX. 1858, and Vol. xn. 1862.

(234) T. H. Huxley. "Lacinularia socialis." Trans, of the Microscopical

Society, 1853.


BIBLIOGRAPHY.


(235) Fr. Leyclig. " Ueb. d. Bau u. d. systematische Stelluny; d. Radcrthiere." Ztit.f. unss. Zool., Vol. vi. 1854.

(236) W. Salensky. "Beit. z. Entwick. von Brachionus urceolaris." Zeit. /. itnss. Zool., Vol. xxn. 1872.

(237) C. Semper. " Zoologische Aphorismen. Trochosphuera axjuatorialis." Zeit.f. wiss. Zool., Vol. xxn. 1872.

MOLLUSCA.

General.

(238) T. H. Huxley. "On the Morphol. of the Cephal. Mollusca." Phil. Trans., 1853.

(239) E. R. Lankester. "On the developmental history of the Mollusca." Phil. Trans., 1875.

(240) H. G. Bronn and W. Keferstein. Die Klasscn u. Ordnungcn d. Thierreichs, Vol. III. 1862-1866.

Gasteropoda and Pteropoda.

(241) J. Alder and A. Hancock. "Devel. of Nudibr." Ann. and Magaz. Nat. Hist., Vol. XH. 1843.

(242) N. Bobretzky. "Studien iiber die embryonale Entwicklung d. Gasteropoden." Archivf. micr. Anat., Vol. xin.

(243) W. K. Brooks. "Preliminary Observations on the Development of Marine Gasteropods." Chesapeake Zoological Laboratory, Session of 1878. Baltimore, 1879.

(244) O. Biitschli. " Entwicklungsgeschichtliche Beitrage (Paludina vivipara)." Zeit.f. wiss. Zool., Vol. xxix. 1877.

(245) W. Carpenter. "On the devel. of the embr. of Purpura lapillus." Trans. Micros. Soc., 2 d series, Vol. ill. 1855.

(246) W. Carpenter. "On the devel. of the Purpura." Ann. and Mag. of Nat. Hist., 2 d series, Vol. xx. 1857.

(247) E. Claparede. "Anatomic u. Entwickl. der Neritina fluviatilis." MUller's Archiv, 1857.

(248) H. Eisig. "Beitr. z. Anat. u. Entwickl. der Geschlechtsorg. von Lymnieus." Zeitschr. f. wiss. Zool., Vol. xix. 1869.

(249) H. Fol. " Sur le developpement des Pteropodes." Archives de Zool. experim. et gtntrale, Vol. iv. 1875.

(250) H. Fol. " Sur le developpement des Gasteropodes pulmones." Compt. rend., 1875, pp. 523526.

(251) H. Fol. "Sur le developpement des Heteropodes." Archives de Zool. expe"rim.etgtn<b-ale,\o\.v. 1876.

(252) C. Gegenbaur. "Beit. z. Entwicklungsgesch. der Landgasteropoden." Zeitschr. f. w. Zool., Vol. ill. 1851.

(253) C. Gegenbaur. Untersuch. iib. Pteropoden u. Hetcropoden. Leipzig, '855.

(254) H. von Jhering. "Entwicklungsgeschichte von Helix." Jcnaische Zcitschrift, Vol. IX. 1875.

(255) W. Keferstein and E. Ehlers. "Beob. lib. d. Entwick. v. Molis peregr." Zool. Beitr., 1861.

(256) J. Koren and D. C. Danielssen. "Benuerk. til Mollusk. Udvikling." NytMag.f. Naturvidensk., Vol. v. 1847. -^"j P- 2O2> '848.

(257) J. Koren and D. C. Danielssen. liidrag til Pectinibr. Udvikl. licrgcn, 1851 (supplement, 1852). Ann. and Mag. Nat. Hist., 1857.

(258) A. Krohn. "Beobacht. aus d. Entwickl. der Pteropoden u. Heterop." Muller's Archiv, 1856 and 1857.

(259) A. Krohn. Beitr. zur Entwickl. der Pteropoden u. Heteropoden. Leipzig, 1860.

(260) H. de Lacaze-Duthiers. "Mem. sur 1'anat.et 1'embryog. des Vermets." 2 partie. Ann. sc. not., 4" srie, T. xm. 1860.

(261) P. Langerhans. "Zur Entwickl. der Gasterop. Opisthobr." Zeitschr. f. w. Zool., Vol. xxni. 1873.


BIBLIOGRAPHY. xi


. E. R. Lankester. "On the development of the Pond-Snail." Quart.

J. of Micr. Scie., Vol. xiv. 1874.

(263) E. R. Lankester. "On the coincidence of the blastopore and anus in Paludina vivipara." Quart. J. of Micr. Scie., Vol. XVI. 1876.

(264) F. Leydig. "Ueber Paludina vivipara." Zeitschr. f. w. Zool., Vol. 11. 1850.

(265) J. MUller. Ueber Synapta dig. u. iib. d. Erzeug. v. Schnecken in Holoth., 1852.

(266) J. Miiller. "Bemerk. aus d. Entwickl. der Pteropoden." Monatsber. Berl. Akad., 1857.

(267) C. Rabl. "Die Ontogenie d. Siisswasser-Pulmonaten." Jenaische Zeitschrift, Vol. IX. 1875.

(268) C. Rabl. "Ueb. d. Entwick. d. Tellerschnecke (Planorbis)." Morph. Jahrbuch, Vol. v. 1879.

(269) W. Salensky. " Beitr. zur Entwickl. d. Prosobr." Zeitschr. f. iv. Zool. , Vol. xxii. 1872.

(270) O. Schmidt. "Ueb. Entwick. von Limax agrestis." Miillcr's Archiv, 1851.

(271) Max S. Schultze. "Ueber d. Entwick. des Tergipes lacinulatus." Arch. f. Naturg., Jahrg. XV. 1849.

(272) E. Selenka. "Entwick. von Tergipes claviger." Niederl. Arch.f. Zool., Vol. I. 1871.

(273) E. Selenka. "Die Anlage d. Keimbl. bei Purpura lapillus." Niederl. Arch.f. Zool., Vol. i. 1872.

(274) C. Semper. "Entwickl. der Ampullaria polita, etc." Natuurk. Verhandl. Utrechts Genootsch., 1862.

(275) An. Stecker. "Furchung u. Keimblatterbildung bei Calyptraa." Morphol. Jahrbuch, Vol. n. 1876.

(276) A.Stuart. " Ueb. d. Entwickl. einiger Opisthobr." Zeitschr. f. w. Zool., Vol. XV. 1865.

(277) N. A. Warneck. "Ueber d. Bild. u. Entwick. d. Embryos bei Gasterop." Bullet. Soc. natural, de Moscou, T. xxm. 1850.

Cephalopoda.

(278) P. J. van Beneden. " Recherches sur 1'Embryogenie des Sepioles." Nouv. Mem. Acad. Roy. de Bruxelles, Vol. xiv. 1841.

(279) N. Bobretzky. Observation on the Development of the Cephalopoda (Russian). Nachrichten d. kaiserlichen Gesell. d. Freunde der Naturwiss. Anthropolog. Rthnogr. bei d. Universitdt Moskau.

(280) H. Grenacher. " Zur Entwicklungsgeschichte d. Cephalopoden." Zeit. f. wiss. Zool., Bd. xxiv. 1874.

(281) A. K6 Hiker. Entwicklungsgeschichte d. Cephalopoden. Zurich, 1844.

(282) E. R. Lankester. "Observations on the development of the Cephalopoda." Quart. J. of Micr. Science, Vol. xv. 1875.

(283) E. Metschnikoff. " Le developpement des Sepioles." Archives d. Sc. phys. et nat., Vol. xxx. Geneve, 1867.

Polyplacophora.

(284) A. Kowalevsky. "Ueb. d. Entwick. d. Chitonen." Zoologischer Anzeiger, No. 37. 1879.

(285) S L. Loven. " Om utvecklingen hos sliigtet Chiton." Stockholm ofversigt, xn. 1855. [Vide also Ann. and Mag. of Nat. Hist., Vol. xvii. 1856, ami Archivf. Naturgeschichte, 1856.]

Scaphopoda.

(286) H. Lacaze-Duthiers. "Developpement du Dentale." Ann. d. Sci.

Nat., Series iv. Vol. VII. 1857.

Lamellibranchiata.

(287) M. Braun. " Postembryonale Entwicklung d. Susswasser-Muscheln."

Zoologischer Garten.


xii BIBLIOGRAPHY.


(288) C. G. Carus. " Neue Untersuch. lib. d. Entvvickl. unscrer FlussmuVcrh. Leop.-Car. Akad., Vol. xvi. 1832.

(289) W. Flemming. " Studien in d. Entwicklungsgeschichte der Najadcn." Sit*, d. k. Akad. Wiss. Wien, Vol. LXXI. 1875.

(290) F. Ley dig. " Ueber Cyclas Cornea." Miiller's Archiv, 1855.

(2111) S. L. Loven. " Bidrag til Kanned. om Utveckl. af Moll. Acephala I^amellibr." Vetensk. Akad. Handl., 1848. [FiVfcalso Arch. f. Naturg., 1849.]

(292) C. Rabl. "Ueber d. Entwicklungsgeschichte d. Malermuschel." Jenaische Zeitschrift, Vol. X. 1876.

(293) W. Salensky. " Bemerkungen uber Haeckels Gastraea-Theorie (Ostrea)." Arch. f. Naturg., 1874.

(294) O. Schmidt. " Ueb. d. Entwick. von Cyclas calyculata." Muller's Arch., 1854.

(295) O. Schmidt. "Zur Entwickl. der Najaden." Wien. Sitzungsber. math.-nat. C!., Vol. xix. 1856.

(296) P. Stepanoff. " Ueber die Geschlechtsorgane u. die Entwicklung von Cyclas." Archivf. Naturgeschichte, 1865.

(297) H. Lacaze-Duthiers. " Ueveloppement d. branchies d. Mollusques Acephales." An. Sc. Nat., Ser. iv. Vol. v. 1856.

POLYZOA. General.

(298) J. Barrois. Recherches sur Cembi yologie des Bryozoaires. Lille, 1877.

Entoprocta.

(299) B. Hatschek. " Embryonalentwicklung u. Knospung d. Pedicellina echinata." Zeitschrift fiir wiss. Zool., Bd. xxix. 1877.

(300) M. Salensky. " Etudes sur les Bryozoaires entoproctes." Ann. Scien. Nat., Ser. vi. Tom. v. 1877.

(301) O. Schmidt. "Die Gattung Loxosoma." Archivf. mik. Anat.,Rd. xii. 1876.

(302) C. Vogt. "Sur le Loxosome des Phascolosomes." Archives de Zool. cxptr. et gtnfr., To.n. v. 1876.

(303) C. Vogt. "Bemerkungen zu Dr Hatschek's Aufsatz lib. Embryonalentwicklung u. Knospung von Pedicellina echinata." Zeit. f. wiss. Zool., Bd. XXX. 1878.

Ectoprocta.

(304) G. J. A 11 man. Monograph of fresh water Polyzoa. Ray Society.

(305) G. J. Allman. " On the structure of Cyphonautes." Quart. J. of Micr. Scie., Vol. xii. 1872.

(306) G. J. Allman. "On the structure and development of the Phylactola> matous Polyzoa." Journal of the Linnean Society, Vol. xiv. No. 77. 1878.

(307) J. Barrois. " Le developpement d. Bryozoaires Chilostomes." Comptes rendus, Sept. 23, 1878.

(308) E. Claparede. " Beitrage zur Anatomic u. Entwicklungsgeschichte d. Seebryozoen." Zeit. fiir wiss. Zool., Bd. xxi. 1871.

(309) E. Claparede. "Cyphonautes." Anat. u. Entwick. wirbell. Thiere. Leipzig, 1864.

(310) R. E. Grant. "Observations on the structure and nature of Flustrae." Edinburgh New Philosoph. Journal, 1827.

(311) B. Hatschek. "Embryonalentwicklung u. Knospung d. Pedicellina echinata" (Description of Cyphonautes). Zeit. f. wiss. Zool., Bd. xxix. 1877.

(312) T. II. Huxley. "Note on the reproductive organs of the Cheilostome Polyzoa." Quart. Jour, of Micr. Science, Vol. IV. 1856.

(313) L. Joliet. "Contributions a 1'histoire naturelle des Bryozoaires des cotes de France." Archives ie Zoologic Experimental, Vol. VI. 1877.

(314) E. Metschnikoff. " Ueber d. Metamorphose einiger Seethiere." Gottingische Nachrichten, 1869.


BIBLIOGRAPHY. xiii


(315) E. Metschnikoff. Bull. deTAcad. de St Pttersbourg, XV. 1871, p. 507.

(316) H. Nitsche. " Beitrage zur Kenntniss d. Bryozoen." Zrit. f. wiss.

Zool., Bd. xx. 1870.

(317) W. Repiachoff. "Zur Naturgeschichte d. chilostomen Seebryozoen." Zeit.f. wiss. Zool., Bd. xxvi. 1876.

(318) W. Repiachoff. " Ueber die ersten Entwicklungsvorgange bei Tendra zostericola. Zeit. f. wiss. Zoo!., Bd. xxx. 1878. Supplement.

(319) W. Repiachoff. "Zur Kenntniss der Bryozoen." Zoologischer Anzeiger, No. 10, Vol. i. 1878.

(320) W. Repiachoff. " Bemerkungen lib. Cyphonautes. " Zoologischer Anzeiger, Vol. n. 1879.

(321) M. Salensky. " Untersuchung an Seebryozoen." Zeit. fur wiss. Zool.. Bd. xxiv. 1874.

(322) A. Schneider. "Die Entwicklung u. syst. Stellung d. Bryozoen u. Gephyreen." Archiv f. mikr. Anaf., Vol. v. 1869.

(323) Smitt. " Om Hafsbryozoernas utveckling och fettkroppar. " Aftryck ur ofvers. of Kong. Vet. Akad. Fork. Stockholm, 1865.

(324) T. Hincks. British Marine Polyzoa. Van Voorst, 1880. [Conf. also works by Farre, Hincks, Van Beneden, Dalyell, Nordmann.]

BRACHIOPODA.

(325) W. K. Brooks. " Development of Lingula." Chesapeake Zoological Laboratory, Scientific Results of the Session of 1878. Baltimore, J. Murphy and Co.

(326) A. Kowalevsky. "Development of the Brachiopoda." Protocol of the First Session of the United Sections of Anatomy, Physiology, and Comparative Anatomy at the Meeting of Russian Naturalists in Kasan, 1873. (Russian.)

(327) H. Lacaze-Duthiers. " Histoire de la Thecidie." Ann. Scien. Nat. etc. Ser. 4, Vol. xv. 1861.

(328) Morse. " On the Early Stages of Terebratulina septentrionalis." Mem. Boston Soc. Nat. History, Vol. n. 1869, also Ann. &> Mag. of Nat. Hist. Series 4, Vol. vm. 1871.

(329) Morse. "On the Embryology of Terebratulina." Mem. Boston Soc. Nat. History, Vol. ill. 1873.

(330) Morse. " On the Systematic Position of the Brachiopoda." Proceedings of the Boston Soc. of Nat. Hist., 1873.

(331) Fritz Miiller. " Beschreibung einer Brachiopoden-Larve." Miiller's Archiv, 1860.

CKLETOPODA.

(332) Alex. Agassiz. "On the young stages of a few Annelids." Annals Lyceum Nat. Hist, of New York, Vol. vm. 1866.

(333) Alex. Agassiz. " On the embryology of Autolytus cornutus and alternations of generations, etc." Boston Journal of Nat. History, Vol. VH. 1859-63.

(334) W. Busch. Beobachtungen it. Anaf. u. Entwick. einiger wirbelloser Seethiere, 1851.

(335) Ed. Claparede. Beobachtungen u. Anat. u. Entwick. 'wirbelloser Thiert an d. Kiiste von Normandie. Leipzig, 1 863.

(336) Ed. Claparede u. E. Metschnikoff. "Beitrage z. Kenntniss lib. Entwicklungsgeschichte d. Chsetopoden." Zeit.f. wiss. Zool., Vol. xix. 1869.

(337) E. Grube. Untersuchungen ub. Entivicklung d. Anneliden. Komgsberg,

4 (338) B. Hatschek. " Beitrage z. Entwick. u. Morphol. d Anneliden." Si/*. d. k. Akad. Wiss. Wien, Vol. LXXIV. 1876.

(339) B. Hatschek. "Studien liber Entwicklungsgeschichte der Anneliden. Arbeiten aus d. zoologischcn Institute d. Universitiit Wien. Von C. Claus. Heft in.

OwQ

(340) Th. H. Huxley. "On hermaphrodite and fissiparous species of tubicolar Annelidse (Protula)." Edinburgh New Phil. Journal, Vol. I. 1855.

(341) N. Kleinenberg. "The development of the earthworm Lumbncus trapezoides." Quart. J, of Micr. Science, Vol. xix. 1879 Sullo ariAtfff del tn<

bricus trapezoides. Napoli, 1878.


XIV BIBLIOGRAPHY.


(342) A. Kowalevsky. " Embryologische Studien an Wiirmern u. Arthropoden." Mem. Acad. Pttersbourg, Series VH. Vol. xvi. 1871.

(343) A. Krohn. " Ueber die Erscheinungen bei d. Fortpfianzung von Syllis prolifera u. Autolytus prolifer." Archiv f. Naturgesch. 1852.

(344) R. Leuckart. " Ueb. d. Jugendzustande ein. Anneliden, etc." Archiv f. Naturgesch. 1855.

(345) S. Love"n. " Beobachtungen ii. die Metamorphose von Anneliden." Wiegmann's Archiv, 1842.

(346) E. Metschnikoff. "Ueber die Metamorphose einiger Seethiere (Mitraria)." Zeit.f. tuiss. Zool., Vol. XXI. 1871.

(347) M. Milne- Ed\vards. " Recherches zoologiques, etc." Ann. Scie. Natur. HI. Se"rie, Vol. ill. 1845.

(348) J. Miiller. "Ueb. d. Jugendzustande einiger Seethiere." Monats. d. k.Akad. Wiss. Berlin, 1851.

(349) Max Miiller. "Ueber d. weit. Entwick. von Mesotrocha sexoculata." Miiller's Archiv, 1855.

(350) Quatrefages. " Memoire s. 1'embryogenie des Annelides." Ann. Scie. Natur. HI. Serie, Vol. x. 1848.

(351) M. Sars. " Zur Entwicklung d. Anneliden." Archiv f. Naturgeschichte, Vol. xi. 1845.

(352) A. Schneider. " Ueber Bau u. Entwicklung von Polygordius." Miiller's Archiv, 1868.

(353) A. Schneider. "Entwicklung u. system. Stell. d. Bryozoen u. Gephyreen (Mitraria)." Archiv f. mikr. Anat. Vol. v. 1869.

(354) M. Schultze. Ueb. die Entwicklung von Arcnicola piscatorum u. anderer Kiemenwurmer. Halle, 1856.

(355) C. Semper. "Die Verwandschaftbeziehungen d. gegliederten Thiere." Arbeiten a. d. zool.-zoot. Instit. Wiirzburg, Vol. in. 1876-7.

(356) C. Semper. "Beitrage z. Biologie d. Oligochjeten." Arbeiten a. d. zool.-zoot. Instit. Wiirzburg, Vol. IV. 1877-8.

(357) M. Stossich. " Beitrage zur Entwicklung d. Chaetopoden." Sitz. d. k. k. Akad. Wiss. Wien, B. LXXVII. 1878.

(358) R. v. Willemoes-Suhm. " Biologische Beobachtungen ii. niedrige Meeresthiere." Zeit.f. wiss. Zool. Bd. xxi. 1871.

DlSCOPHORA.

(359) O. BUtschli. " Entwicklungsgeschichtliche Beitrage (Nephelis)." Zeit. f. wiss. Zool. Vol. xxix. 1877.

(360) E. Grube. Untersuchungen ub. d. Entwicklung d. Anneliden. Konigsberg, 1844.

(361) C. K. Hoffmann. "Zur Entwicklungsgeschichte d. Clepsineen." NICderland. Archiv f. Zool. Vol. IV. 1877.

(362) R. Leuckart. Die menschlichen Parasiten (Hirudo}, Vol. I. p. 686, et seq.

(363) H. Rathke. Beit. z. Entwicklungsgesch. d. Hirudineen. Leipzig, 1862.

(364) Ch. Robin. Mem. snr le Developpement embryogenique des Ilirndiih'c*. Paris, 1875.

(365) C. O. Whitman. "Embryology of Clepsine." Quart. J. of Micro. Science, Vol. xvm. 1878.

[ Vide also C. Semper (No. 355) and Kowalevsky (No. 342) for isolated observations.]

GEPHYREA. GepJiyrea nuda.

(366) A. Kowalevsky. Sitz. d. zool. Abth. d. Iff. Versam. rtiss. Naturf (Thalassema). Zeit.f. wiss. Zool. Vol. xxn. 1872, p. 284.

(367) A. Krohn. "Ueb. d. Larve d. Sipunculus nudus ncbst I'.c UK iknii^cn, ' etc. Miiller's Archiv, 1857.


BIBLIOGRAPHY. xv


(368) M. Salensky. " Ueber die Metamorphose d. Echiurus." Morfhohgisches Jahrbuch, Bd. 11.

(369) E. Selenka. "Eifurchung u. Larvenbilflung von Phascolosoma elongatum." Zeit.f. wiss. Zool. 1875, Bd- xxv. p. i.

(370) J. W. Spengel. " Beitrage z. Kenntniss d. Gephyreen (lionellia)." MitlheiL a. d. zool. Station z. Neapel, Vol. i. 1879.

Gephyrea tubicola (Actinotroc/ia).

(371) A. Krohn. " Ueb. Pilidium u. Actinotrocha." Muller's Archiv, 1858.

(372) A. Kowalevsky. " On anatomy and development of Phoronis," Petersburg, 1867. i PI. Russian. Vide Leuckart's Bcricht, 1866-7.

(373) E. Metschnikoff. " Ueber d. Metamorphose einiger Seethiere (Actinotrocha)." Zeit.f. wiss. Zool. Bd. XXI. 1871.

(374) J. Miiller. " Bericht ub. ein. Thierformen d. Nordsee." Muller's Archiv, 1846.

(375) An. Schneider. "Ueb. d. Metamorphose d. Actinotrocha branchiata." Muller's Arch. 1862.

CH^TOGNATHA.

(376) O. Butschli. " Zur Entwicklungsgeschichte der Sagitta." Zeilschrifl f. wiss. Zool., Vol. xxin. 1873.

(377) C. Gegenbaur. "Ueber die Entwicklung der Sagitta." Abhand. d. natiirforschenden Gesellschaft in Halle, 1857.

(378) A. Kowalevsky. " Embryologische Studien an Wiirmern u. Arthropoden." Mem. Acad. Petersbourg, vn. ser., Tom. xvi., No. 12. 1871.

MYZOSTOMEA.

(379) L.Graff. Das Genus Myzostoma. Leipzig, 1877.

(380) E. Metschnikoff. "Zur Entwicklungsgeschichte d. Myzostomum." Zeit.f. wiss. Zool., Vol. xvi. 1866.

(381) C. Semper. "Z. Anat. u. Entwick. d. Gat. Myzostomum." Zeit.f. wiss. Zool., Vol. IX. 1858.

GASTROTRICHA.

(382) H. Ludwig. " Ueber die Ordnung Gastrotricha Metschn." Zeit.f. wiss. Zool., Vol. xxvi. 1876.

NEMATELMINTHES.

(383) O. Butschli. "Entwicklungsgeschichte d. Cucullanus elegans." Zeit. f. wiss. Zool., B. xxvi. 1876.

(384) T. S. Cobbold. Entozoa. Groombridge and Son, 1864.

(385) T. S. Cobbold. Parasites; a Treatise on the Entozoa of Man and Animals. Churchill, 1879.

(386) O. Caleb. "Organisation et developpement des Oxyurides, etc. Archives de Zool. exper. et gener., Vol. VII. 1878.

(387) R. Leuckart. Untersuchungeniib. Trichina spiralis. 2nd ed. Leipzig, 1866.

(388) R. Leuckart. Die menschlichen Parasiten, Bd. u. 1876.

(389) H. A. Pagenstecher. Die Trichinen nach Versuchen dargestellt.

(390) A.Schneider. Monographie d. Nematoden. Berlin, 1866.

(391) A. Villot. " Monographie des Dragoneaux " (Gordioidea). Archives de Zool. exptr. et gtner., Vol. in. 1874.

ACANTHOCEPHALA.

(392) R. Greeff. " Untersuchungen u. d. Ban u. Entwicklung des Echin. miliarius." Archiv f. Naturgesch. 1864.

(393) R. Leuckart. Die menschlichen Parasiten. Vol. 11. p Soi ol


xvi BIBLIOGRAPHY.


(394) An. Schneider. " Ueb. d. Bau d. Acanthocephalen." Archiv f. Anat. w. Phys. 1868.

(395) G. R. Wagener. Beitrdge z. Entrvicklungsgeschichte d. Eingeweidewiirmer. Haarlem, 1865.

TRACHEATA.

PRO TO TRA CHE A TA .

(396) H. N. Moseley. "On the Structure and Development of Peripatus capensis." Phil. Trans. Vol. 164, 1874.

MYRIAPODA.

(397) G. Newport. "On the Organs of Reproduction and Development of the Myriapoda." Philosophical Transactions, 1841.

(398) E. Metschnikoff. " Embryologie der doppeltfiissigen Myriapoclen (Chilognatha)." Zeit.f. wiss. Zool., Vol. xxiv. 1874.

(399) E. Metschnikoff. " Embryologisches iiber Geophilus." Zeit. f. wiss. 'Zool., Vol. xxv. 1875.

(400) Anton Stecker. "Die Anlage d. Keimblatter bei den Diplopoden." Archiv f. mik. Anatomic, Bd. xiv. 1877.

INSECTA.

(401) M Balbiani. " Observations s. la reproduction d. Phylloxera du Chene." An. Sc. Nat. Ser. v. Vol. xix. 1874.

(402) E. Bessels. "Studien u. d. Entwicklung d. Sexualdrtisen bei den Lepidoptera." Zeit.f. miss. Zool. Bd. xvn. 1867.

(403) Alex. Brandt. " Beitrage zur Entwicklungsgeschichte d. Libellulida u. Hemiptera, mit besonderer Beriicksichtigung d. Embryonalhiillen derselben." Mem. Ac. Pttersbourg, Ser. vn. Vol. xin. 1869.

(404) Alex. Brandt. Ueber das Ei u. seine Bildungsstdtte. Leipzig, 1878.

(405) O. Butschli. " Zur Entwicklungsgeschichte d. Biene." Zeit. f. wiss. Zool. Bd. xx. 1870.

(406) H. Dewitz. "Bau u. Entwicklung d. Stachels, etc." Zeit.f. wiss. Zool. Vols. xxv. and xxvin. 1875 and 1877.

(407) H. Dewitz. "Beitrage zur Kenntniss d. Postembryonalentwicklung d. Gliedmassen bei den Insecten." Zeit. /. wiss. Zool. xxx. Supplement. 1878.

(408) A. Dohrn. "Notizen zur Kenntniss d. Insectenentwicklung." Zeitschriftf. wiss. Zool. Bd. xxvi. 1876.

(409) M. Fabre. " L'hypermetamorphose et les mceurs des Meloides." An. Sci. Nat. Series iv. Vol. vn. 1857.

(410) Ganin. "Beitrage zur Erkenntniss d. Entwicklungsgeschichte d. Insecten." Zeit. f. wiss. Zool. Bd. xix. 1869.

(411) V. Graber. Die Insecten. Miinchen, 1877.

(412) V. Graber. " Vorlauf. Ergeb. lib. vergl. Embryologie d. Insecten." Archiv f. mikr. Anat. Vol. XV. 1878.

(413) O.v.Grimm. " Ungeschlechtliche Fortpflanzung einer Chironomus-Art u. deren Entwicklung aus dem unbefruchteten Ei." Mhn. Acad. Pttcrsbourg. 1X70.

(414) B. Ilatschek. " Beitrage zur Entwicklung d. Lepidopteren." Jenaischc Zeitschrift, Bd. xi.

(415) A. Kollikcr. " Observationes de prima insectorum gcnese, etc. " Ann. Sc. Nat. Vol. xx. 1843.

(11(5) A. Kowalevsky. " Embryologische Studien an Wiirmern u. Arthropoden." Mtm. Ac. imp. J\'(,-rstn>nr, Ser. VII. Vol. XVI. iSji.

(417) C. Kraepelin. " Untersuchungen lib. d. Bau, Mechanismus u. d. Entwick. des Stachels d. l.icnartigai Tliicrc." Zeit.f. wiss. Zool. Vol. xxm. 1X7.5.

(418) C. Kupffcr. " Faltcnblatt nn d. Embryoncn d. Gattung Chirononnis." Arch.f. mikr. Anat. Vol. n. iS66.

(419) R. Leuckart. Zur Kemituiss d. Gi'ncratiomxi'ffhscls it. d. /'/; -Ihetii^ , < b. d. Insecten. Frankfurt, iH.nS.


BIBLIOGRAPHY. xvii


(420) Lubbock. Origin and Metamorphosis of Insi-cts. 1874.

(421) Lubbock. Monograph on Collembola ami Thysanura. Ray Society, 1873 (422) Melnikow. " Beitrage z. Embryonalentwicklung d. Insecten." Archiv f. Naturgeschichte, Bd. XXXV. 1869.

(423) E. Metschnikoff. ' ' Embryologische Studien an Insecten." '/.fit. /. wiss. Zool Bd. xvi. 1866.

(424) P. Meyer. " Ontogenie und Phylogenie d. Insecten." Jcnaischt Zfitschrift, Vol. X. 1876.

(425) Fritz Miiller. " Beitrage z. Kenntniss d. Termiten." Jcnaische Zeitschrift, Vol. IX. 1875.

(426) A. S. Packard. " Embryological Studies on Diplex, Perithemis, and the Thysanurous genus Isotoma." Mem. Pea body Acad. Science, \. 2. 1871.

(427) Suckow. " Geschlechtsorgane d. Insecten." Heusinger's Zeitschrift f. organ. Physik, Bd. II. 1828.

(428) Tichomiroff. " Ueber die Entwicklungsgeschichte des Seidenwiirms." Zoologischer Anzeigcr, n. Jahr. No. 20 (Preliminary Notice).

(429) Aug. Weismann. "Zur Embryologie d. Insecten." Arehiv f. Anat. und Phys. 1864.

(430) Aug. Weismann. " Entwicklung d. Dipteren." Zeit. f. wiss. Zool. Vols. xni. and xiv. Leipzig, 1863 4.

(431) Aug. Weismann. " Die Metamorphose d. Corethra plumicornis." Ztit. f. unss. Zool. Vol. xvi. 1866.

(432) N. Wagner. " Beitrag z. Lehre d. Fortpflanzung d. Insectenlarven." Zeit.f. wiss. Zool. Vol. Xlll. 1860.

(433) Zaddach. Untersuchnngen tib. d. Bau u. d. Enhuicklung d. Gliederlhifre. Berlin, 1854.

ARACHNID A. Scorpionidce.

(434) El. Metschnikoff. " Embryologie des Scorpions." Zeit.f. unss. Zool. Bd. xxi. 1870.

(435) H. Rathke. Reisebemerknngen aus Taurien (Scorpio), Leipzig, 1837.

Pseudoscorpionidce.

(436) El. Metschnikoff. " Entwicklungsgeschichte d. Chelifer." Zeit.f. unss. Zool. Bd. xxi. 1870.

(437) A. Stecker. "Entwicklung der Chthonius-Eier im Mutterleibe und c Bildung des Blastoderms." Sitzung. konigl. bohmisch. Gesellschaft Wissensch. t 1876, 3. Heft, and Annal. and Mag. Nat. History, 1876, xvill. 197.

Phalangida.

(438) M. Balbiani. " Memoire sur le developpement des Phalangides." Ann. Scien. Nat. Series v. Vol. xvi. 1872.

Araneina.

(439) M. Balbiani. "Memoire sur le developpement des Araneides." Ann. Scien. Nat. Series v. Vol. xvn. 1873. /->./

(440) F. M. Balfour. "Notes on the development of the Arane

Journ. of Micr. Science, Vol. XX. 1880. v ,

(441) J. Barrois. " Recherches s. 1. developpement des Araign^es.

de I' Anat. et de la Physiol. 1878. , , fiA

(442) E. Claparede. Recherches s. revolution des Aratgnees. Jtrecht, 1862.

(443) Her old. De generation Araneorum in Ovo. Marburg, 1824.

(444) H. Ludwig. "Ueber die Bildung des Blastoderms bei den Zeit.f. wiss. Zool. Vol. xxvi. 1876.

B. II. b


xviii BIBLIOGRAPHY.


Acariua.

(445) P. van Beneden. " Developpement de 1'Atax ypsilophora." Acad. Bruxelles, t. xxiv.

(446) Ed. Claparede. "Studien uber Acarinen." Zeit. /. wits. Zoo/., Bd. xvin. 1868.

CRUSTACEA. General Works.

(447) C. Spence Bate. " Report on the present state of our knowledge of the Crustacea." Report of the British Association for 1878.

(448) C. Claus. Untersuchungen zur Erforschung der genealogischen Grundlage des Crustaceen -Systems. Wien, 1876.

(449) A. Dohrn. "Geschichte des Krebsstammes. " Jenaische Zeitschrift, Vol. vi. 1871.

(450) A. Gerstaecker. Bronris Thierreich, Bd. v. Arthropoda, 1866.

(451) Th. II. Huxley. The Anatomy of Invertebrated Animals. London, 1877.

(452) Fritz Miiller. Fiir Darwin, 1864. Translation, Facts for Darwin. London, 1869.

Branchiopoda.

(453) Brauer. "Vorlaufige Mittheilung iiber die Entwicklung u. Lebensweise des Lepidurus (Apus) productus." Sitz. der Ak. d. Wiss. Wien, Vol. LXIX., 1874.

(454) C. Claus. ' Zur Kenntniss d. Baues u. d. Entwicklung von Branchipus stagnalisu. Apuscancriformis." Abh. d. konig. Gesell. der Wiss. Gbttingen, Vol. xviii.

l8 '3-_

(455) C. Grobben. "Zur Entwicklungsgeschichte d. Moina rectirostris." Arbeit, a. d. zoologisch. Institute Wier., Vol. II., 1879.

(456) E. Grube. " Bemerkungen iiber die Phyllopoden nebst einer Uebersicht etc." Archivf. Naturgcschichte, Vol. xix., 1853.

(457) N. Joly. " Histoire d'un petit Crustace (Artemia salina, Leach) etc." Annales d. Sciences Natur., 2nd ser., Vol. xiir., 1840.

(458) N. Joly. " Recherches zoologiques anatomiques et physiologiques sur 1' I sauracy clad oides ( = Esther ia) nouveau genre, etc." Annales d. Sciences Nat., 2nd ser., Vol. xvii., 1842.

(459) Lereboullet. " Observations sur la generation et le de veloppement de la Limnadia de Hermann." Annales d. Sciences Nattir., ^th ser., Vol. v., 1866.

(460) F. Ley dig. " Ueber Artemia salina u. Branchipus stagnalis." Zeit. f. wiss. Zool., Vol. in., 1851.

(461) G. O. Sars. "Om en dimorph Udvikling samt Generationsvexel hos I^eptodora." Vidensk. Selskab. For hand, 1873.

(462) G. Zaddach. De apodis cancrefortnis Schaeff. anatome ct historia evolutionis. Dissertatio inanguralis zootomica. Bonnae, 1841.


Nebaliadce.

(463) C. Claus. " Ueber den Bau u. die systematische Stellung von Nebalia." Zeit.f. wiss. Zool., 15d. xxn. 1872.

(464) E.Metschnikoff. Development of Nebalia ( Russian), 1 868.

Schizopoda.

(465) E. van Beneden. "Recherches sur 1'Embryogenie des Crustace's. u. Developpement des Mysis." liullet. de rAcadc ! mie roy. de Belgique, second series, Tom. xxvin. 1869.

(46H) C. Claus. " Ueber einige Schizopoden u. niedere Malakostraken." Zeit. /. -t'tss. Zoologie, Bd. XIII., 1863.


BIBLIOGRAPHY. xix


(467) A. Dohrn. " Untersuchungen iib. Bau u. Entwicklung d. Arthropoden." Zeit. f. wiss. Zool., Bd. xxi., 1871, p. 375. Peneus zoaea (larva of Euphausia).

(468) E. Metschnikoff. " Ueber ein Larvenstadium von Euphausia." Zeit. fiir wiss. Zool., Bd. xix., 1869.

(469) E. Metschnikoff. " Ueber den Naupliuszustand von Euphausia." Zeit. fiir wiss. Zool., Bd. xxi., 1871.

Decapoda.

(470) Spence Bate. "On the development of Decapod Crustacea." Phil. Trans., 1858.

(471) Spence Bate. " On the development of Pagurus." Ann. and Mag. Nat. History, Series 4, Vol. 1 1., 1868.

(472) N. Bobretzky. Development of Astacus and Paluemon. Kiew, 1873. (Russian.)

(473) C. Claus. "Zur Kenntniss d. Malakostrakenlarven." Wiirzb. naturw. Zeitschrift, 1861.

(474) R. Q. Couch. "On the Metamorphosis of the Decapod Crustaceans." Report Cornwall Polyt. Society, 1848.

(475) Du Cane. "On the Metamorphosis of Crustacea." Ann. and Mag. of Nat. History, 1839.

(476) Walter Faxon. " On the development of Paloemonetes vulgaris." Bull. of the Mus. of Comp. Anat. Harvard, Cambridge, Mass., Vol. V., 1879.

(477) A. Dohrn. " Untersuchungen iib. Bau u. Entwicklung d. Arthropoden." " Zur Entwicklungsgeschichte der Panzerkrebse. Scyllarns Palinurus." Zeit. f. wiss. Zool., Bd. xix., 1870.

(478) A. Dohrn. "Untersuchungen iib. Bau u. Entwicklung d. Arthropoden. Erster Beitrag z. Kenntniss d. Malacostrakcn u. ilirer Larven Amphion Reynaudi, Lophogaster, Portunus, Porcellanus, Elaphocaris. " Zeit. f. ^viss. Zool., Bd. XX., 1870.

(479) A. Dohrn. "Untersuchungen iib. Bau u. Entwicklung d. Arthropoden. Zweiter Beitrag, etc." Zeit.f. wiss. Zool., Bd. XXI., 1871.

(480) N. J oly. " Sur la Caridina Desmarestii." Ann. Scien. Nat., Tom. xix., 1843.

(481) Lereboullet. " Recherches d. 1'embryologie comparee sur le developpement du Brochet, de la Perche et de 1'Ecrevisse." Mem. Savuns Etrang. Paris, Vol. xvii., 1862.

(482) P. Mayer. "Zur Entwicklungsgeschichte d. Dekapoden." Jenaische Zeitschrift, Vol. XI., 1877.

(483) Fritz Miiller. '* Die Verwandlung der Porcellana." Archivf. Naturgeschichte, 1862.

(484) Fritz Miiller. " Die Verwandlungen d. Garneelen." Archivf. Naturgesch., Tom. xxix.

(485) Fritz Miiller. " Ueber die Naupliusbrut d. Garneelen." Zeit. f. wiss. Zool., Bd. xxx., 1878.

(486) T. J. Parker. "An account of Reichenbach's researches on the early development of the Fresh-water Crayfish." Quart. J. of M. Science, Vol. xvui., 1878.

(487) H. Rathke. Ueber die Bildung u. Entwicklung d. Flusskrebses. Leipzig, 1829.

(488) H. Reichenbach. " Die Embryoanlage u. erste Entwicklung d. Flusskrebses." Zeit. f. wiss. Zool., Vol. xxix., 1877.

(489) F. Richters. "Ein Beitrag zur Entwicklungsgeschichte d. Loricaten." Zeit.f. wiss. Zool., Bd. xxiii., 1873.

(490) G. O. Sars. " Om Hummers postembryonale Udvikling." Vidcnsk Selsk. Forh. Christiania, 1874.

(491) Sidney J. Smith. " The early stages of the American Lobster. " Tratts. of the Connecticut Acad. of Arts and Sciences, Vol. II., Part i, 1873.

(492) R. v. Willemoes Suhm. " Preliminary note on the development of some pelagic Decapoda." Proc. of Royal Society, 1876.


XX BIBLIOGRAPHY.


Stomatopoda.

(41KI) \V. K. Brooks. " On the larval stages of Squilla empusa. Chesapeake Zoological Laboratory^ Scientific results of the Session ^1878. Baltimore, 1879.

(494) C. Claus. "Die Metamorphose der Squilliden." Abhand. dcr konigl. Gesell. der IViss. ztt Gottingen^ 1*7-.

( 1 '.!">) Fr. M tiller. 4i Bruchstuck a. der Entwicklungsgeschichte d. Maulfiisser I. und II." Archivf. Naturgeschichte, Vol. xxvni., 1862, and Vol. XXIX., 1863.

Cumacea*

( 1%) A. Dohrn. " Ueber den Bau u. Entwicklung d. Cumaceen." Jenaische Zeitschrift, Vol. v., 1870.

hopoda.

(497) Ed. van Beneden. " Recherches sur 1'Embryogenie des Crustaces. i. Asellus aquaticus." BiuL de FAcad. roy. Belgique, 2me serie, Tom. XXVIII., No. 7, 1869.

(498) N. Bobretzky. "Zur Embryologie des Oniscus murarius." Ztit. fur wiss. Zool., Bd. xxiv., 1874.

(4119) J. F. Bullar. "On the development of the parasitic Isopoda." Phil. Trans., Part n., 1878.

(500) A. Dohrn. " Die embryonale Entwicklung des Asellus aquaticus." Zeit. f. wiss. Zool., Vol. xvii., 1867.

(501) II. Rathke. Untersuchungen iibcr die Bildung und Entwicklung der VVasser-Assel. Leipzig, 1832.

(5u2) H. Rathke. Zur Morphologic. Reisebemerkungen aus J^aurien. Riga u. Leipzig, 1837. (Bopyrus, Idothea, Ligia, lanira.)

. A mphipoda.

(503) Ed. van Beneden and E. Bessels. "Memoire sur la formation du blastoderme chez les Amphipodes, les Lerneens et les Copepodes." Classe des Sciences de F Acad. roy. de Belgiqtie, Vol. xxxiv., 1868.

(004) De la Valette St George. " Studien liber die Entwicklung der Amphipoden." Abhand. d. naturfor. Gesell. zu Halle, Bd. v., 1860.

Copcpoda.

(505) E. van Beneden and E. Bessels. "Memoire sur la formation du blastoderme chez les Amphipodes, les Lerneens et Copepodes." Classe des Sciences dc FAcad. roy. de Bel^ique, Vol. xxxiv., 1868.

(">(Hi) E. van Beneden. " Recherches sur 1'Embryoge'nie des Crustaces I v. Anchorella, Lerneopoda, Branchiella, Hessia." Bull, de FAcad. roy. de Belgique^ sme serie, T. xxix., 1870.

(507) C. Claus. Zur Anatomie u. Entwicklungsgeschichte d. Copepoden.

("iii.S) C. Claus. " Untcrsuchungen iiber die Organisation u. N'crwaiulschaft d. Copepoden." Witrzburger nalttnviss. Zeitschrift, Bd. ill., 1862.

(.")('.() C. Claus. ' Ueber den Bau u. d. Entwicklung von Achtheres percarum." '/.cit.f. wiss. Zool., Bd. XI., 1862.

I ."> 1 ( i ) C . (' 1 a u s. Die frcilcbcnden Copepoden mit bcsonderer Beritcksichtigiing der Fauna Dcutschlands, der Nordsec u. des Mitteltnecres. Leip/.i.^, 1863.

(511) C. C laus. " Ueber d. Entwicklung, Organisation u. systematische Stellung d. Arguliihv." /.eit. f. wiss. tool., P>d. xxv., 1875.

(51^) P. P. C. Hoek. "Zur Entwicklungsgeschichte d. Entomostracen." Niederliindischcs Archiv, Vol. IV., 1877.

(513) N o rd m a n n. Mikrographische Beitrdge zur Naturgeschichte der ivirbcllosen Thiert Z\\ cites Heft. 1832.

|.">M) Salensky. " Sphseronella Leuckartii." Archivf. Naturgcschichtc, 1868.

(515) F. Vejdovsky. "Untersuchnngen lib. d. Anat. u. Mctamorph. v. Trachcliastes polycolpus " Zcit.f. wiss. Zool., Vol. xxix., 1877.


BIBLIOGRAPHY. xxi


Cirripedia.

(516) C. Spence Bate. "On the development of the Cirripedia." Annals and Mag. of Natur. History. Second Series, vm., 1851.

(517) E. van Beneden. " Developpement des Sacculines." Bull, de F Acad. roy. de Belg., 1870.

(518) C. Claus. Die Cypris-dhnliehe Larve der Cirripedien. Marburg, 1869.

(519) Ch. Darwin. A monograph of the sub-class Cirripedia, i Vols., Kay Society, 1851 4.

(520) A. Dohrn. " Untersuchungen iibcr Bau u. Entwicklung d. Arthropoden ix. Eine neue Naupliusform (Archizoea gigas)." Zeit. f. wiss. Zool., Bd. XX., 1870.

(521) P. P. C. Hoek. "Zur Entwicklungsgeschichte der Entomostraken I. Embryologie von Balanus." Wiederlandisches Archiv fur Zoologic, Vol. III., 1876 7.

(522) R. Kossmann. " Suctoria u. Lepadidze. Arbeiten a. d. zool.-zoot. Instituted. Univer. Wiirz., Vol. I., 1873.

(523) Aug. Krohn. " Beobachtungen iiber die Entwicklung der Cirripedien." Wiegmanrfs Archiv fur Naturgesch., xxvi., 1860.

(524) E. Metschnikoff. Sitzungsberichte d. Versammlung deutscher Naturforscher zu Hannover ; 1865. (Balanus balanoides.)

(525) Fritz Muller. "Die Rhizocephalen." Archiv /. Naturgeschichte, 18623.

(526) F. C. Noll. "Kochlorine hamata, ein bohrendes Cirriped." Zeit.f. wiss. Zool., Bd. xxv., 1875.

(527) A. Pagenstecher. " Beitrage zur Anatomic und Entwicklungsgeschichte von Lepas pectinata." Zeit.f. wiss. Zoo/., Vol. xin., 1863.

(52tt) J. V. Thompson. Zoological Researches and Illustrations, Vol. I., Part I. Memoir iv. On the Cirripedes or Barnacles. 8vo. Cork, 1830.

(529) J. V. Thompson. " Discovery of the Metamorphosis in the second type of the Cirripedes, viz. the Lepades completing the natural history of these singular animals, and confirming their affinity with the Crustacea." Phil. Trans. 1835. P art n.

(530) R. von Willemoes Suhm. "On the development of Lepas fascicularis." Phil. Trans., Vol. 166, 1876.

Ostracoda.

(531) C. Claus. " Zur naheren Kenntniss der Jugendformen von Cypris ovum." Zeit.f. wiss. Zool., Bd. XV., 1865.

(532) C. Claus. "Beitrage zur Kenntniss d. Ostracoden. Entwicklungsgeschichte von Cypris ovum." Schriften d. Gesell. zur Bejorderung d. gesamm. Naturwiss. zu Marburg, Vol. IX., 1868.

PCECILOPODA.

(533) A. Dohrn. "Untersuch. lib. Bau u. Entwick. d. Arthropoden (Limulus polyphemus)." Jcnaische Zeitschrift, Vol. VI., 1871.

(534) A. S. Packard. "The development of Limulus polyphemus." Mem. Boston Soc. Nat. History, Vol. II., 1872.

PYCNOGONIDA.

(535) G. C a van n a. " Studie e ricerche sui Picnogonidi." PiMIicazioni del R. Instittito di Studi super iori in Firenze, 1877.

(536) An. Dohrn. " Ueber Entwicklung u. Bau d. Pycnogoniden." Jenaische Zeitschrift, Vol. v. 1870, and "Neue Untersuchungen ub. Pycnogoniden." Mittheil. a. d. zoologischen Station zu Ncapel, Bd. I. 1878.

(537) G. Hodge. " Observations on a species of Pycnogon, etc." Annal. and Mag. of Nat. Hist. Vol. ix. 1862.

(538) C. Semper. " Ueber Pycnogoniden u. ihre in Hydroiden schmarotzenden Larvenformen. 1 ' Arbeiten a. d. zool.-zoot. Instit. IViiizburg, Vol. I. 1874.


xxii BIBLIOGRAPHY.


PENTASTOMIDA.

(539) P. T. van Ben e den. " Recherches s. 1'organisation et le developpement d. Linguatules. Ann. d. Scien. Nat., 3 Ser., Vol. XI.

("I'M R. Leuckart. " Bau u. Entwicklungsgeschichte d. Pentastomen." Leipzig and Heidelberg. 1860.

TARDIGRADA.

(541) J. Kaufmann. " Ueber die Entwicklung u. systematische Stellung d. Tardigraden." Zeit.f. iviss. Zool., Bd. ill. 1851.

ECHINODERMATA.

(542) Alex. Agassiz. Revision of the Echini. Cambridge, U.S. 1872 74.

(543) Alex. Agassiz. " North American Starfishes." Memoirs of the Museum of Comparative Anatomy and Zoology at Harvard College, Vol. v., No. i. 1877 (originally published in 1864).

(544) J. Barrois. " Embryogenie de 1'Asteriscus verruculatus " Journal de VAnat. et Phys. 1879.

(545) A. Baur. Beitrdge zur Naturgeschichte d. Synapta digitata. Dresden, 1864.

(546) H. G. Bronn. Kiassen u. Ordnungen etc. Strahlenthiere, Vol. II. 1860.

(547) W. B. Carpenter. "Researches on the structure, physiology and development of Antedon." Phil. Trans. CLVI. 1866, and Proceedings of the Roy. Soc., No. 166. 1876.

(548) P. H. Carpenter. " On the oral and apical systems of the Echinoderms." Quart. J. of Micr. Science, Vol. xvni. and xix. 1878 9.

(549) A. Gotte. " Vergleichende Entwicklungsgeschichte d. Comatula mediterranea." Arch.fiir micr. Anat., Vol. xn. 1876.

(550) R. Greeff. "Ueber die Entwicklung des Asteracanthion rubens vom Ei bis zur Bipinnaria u. Brachiolaria." Schriftcn d. Gesellschaft zur Beforderung d. gesarnmlen Natnrwissenschaften zu Marburg, Bd. XII. 1876.

(551) R. Greeff. "Ueber den Bau u. die Entwicklung d. Echinodermen." Sitz. d. Gesell. z. Beforderung d. gesam. Naturwiss. zu Marburg, No. 4. 1879.

(552) T. H. Huxley. "Report upon the researches of Mliller into the anat. and devel. of the Echinoderms." Ann. and Mag. of Nat. Hist., 2nd Ser., Vol. vin.

(553) Koren and Danielssen. "Observations sur la Bipinnaria asterigera." Ann. Scien. Nat., Ser. in., Vol. VII. 1847.

i-">l) Koren and Uanielssen. "Observations on the development of the Starfishes." Ann. and Mag. of Nat. Hist., Vol. XX. 1857.

(."..",.",) A. Kowalevsky. "Entwicklungsgeschichte d. Holothurien." Aft m. Ac. Petersburg, Ser. VII., Tom. XI., No. 6.

("'"><') A. Krohn. "Beobacht. a. d. Entwick. d. Holothurien u. Seeigel." M tiller's Archiv, 1851.

(Vi7) A. Krohn. " Ueb. d. Entwick. d. Seesterne u. Holothurien." Muller's Ardiir,

A. Krohn. "Beobacht. lib. Echinodermenlarven." Miiller's Archiv, 18(4.

('>'>'.)} II. Ludwig. "Ueb. d. primar. Steinkanal d. Crinoideen, nebst vergl. anat. Bemerk. ub. d. Echinodermen." Zeit.f. wiss. Zoo/., Vol. xxxiv. iSSo.

(">r,n) K. Metschnikoff. "Studien lib. d. Entwick. d. Echinodermen u. Nemertinen." Mem. .!< . J', : /i'rsfa>nr?. Scries VII., Tom. XIV., No. 8. 1869.

(501)' Joh. Miillcr. " Ueb. d. Larven u. d. Metamorphose d. EchinodcM men.' Alhandlnng,-n d. />>///'. Akad. (Five Memoirs), 1848, 49, 50. 52 (two Mnnoirs).

Joh. Miiller. " Allgemeincr Plan d. Entwicklung d. Echinodermen. Abhandl. d. Berlin. Akad., 1853.

1 The dates in this reference are the dates of publication.


BIBLIOGRAPHY. xxiil


(563). E. Selenka. "Zur Entwicklung d. Holothurien." Ztit. f. wiss. Zoo/., Ed. xxvn. 1876.

(564) E. Selenka. "Keimblatter u. Organanlage bei Echiniden." Zeit.f.wiss. Zool.t Vol. xxxni. 1879.

(565) Sir Wyville Thomson. " On the Embryology of the Echinodcrmata." Natural History Review, 1864.

(566) Sir Wyville Thomson. "On the Embryogeny of Antedon rosacetw." Phil. Trans. 1865.

ENTEROPNEUSTA.

(567) A. Agassiz. "Tornaria." Ann. Lyceum Nat. Hist. vin. New York, 1866.

(568) A. Agassiz. "The History of Balanoglossus and Tornaria." Mem. Amer. Acad. of Arts and Scien., Vol. IX. 1873.

(569) A. Gotte. " Entwicklungsgeschichte d. Comatula Mediterranea. " Archiv fur mikr. Anat., Bd. XII., 1876, p. 641.

(570) E. Metschnikoff. " Untersuchungen lib. d. Metamorphose, etc. (Tornaria)." Zeit.fiir wiss. Zool., Bd. XX. 1870.

(571) J. M tiller. " Ueb. d. Larven u. Metamor. d. Echinodermen." Berlin. Akad., 1849 and 1850.

(572) J. W. Spengel. "Bau u. Entwicklung von Balanoglossus." Tagebl.d. Naturf. Vers. Mtinchen, 1877.


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