The Works of Francis Balfour 3-24: Difference between revisions

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2 These views fit in very well with those already put forward in Chapter xm. on  
2 These views fit in very well with those already put forward in Chapter xm. on  
the affinities of the Echinodermata.  
the affinities of the Echinodermata.
 
 
 
==Chapter XXV. The Alimentary Canal and its Appendages, in the Chordata==
 
The alimentary canal in the Chordata is always formed of
three sections, analogous to those so universally present in the
Invertebrata. These sections are (i) the mesenteron lined by
hypoblast ; (2) the stomodaeum or mouth lined by epiblast, and
(3) the proctodaeum or anal section lined like the stomodaeum by
epiblast.
 
Mesenteron.
 
The early development of the epithelial wall of the mesenteron
has already been described (Chapter XI.). It forms at first a
simple hypoblastic tube extending from near the front end of the
body, where it terminates blindly, to the hinder extremity where
it is united with the neural tube by the neurenteric canal (fig.
420, ne). It often remains for a long time widely open in the
middle towards the yolk-sack.
 
It has already been shewn that from the dorsal wall of the
mesenteron the notochord is separated off nearly at the same
time as the lateral plates of mesoblast (pp. 292 300).
 
The subnotochordal rod. At a period slightly subsequent
to the formation of the notochord, and before any important
differentiations in the mesenteron have become apparent, a
remarkable rod-like body, which was first discovered by Gotte,
becomes split off from the dorsal wall of the alimentary tract in
all the Ichthyopsida. This body, which has a purely provisional
existence, is known as the subnotochordal rod.
 
 
 
MESENTERON.
 
 
 
755
 
 
 
It develops in Elasmobranch embryos in two sections, one situated in
the head, and the other in the trunk.
 
The section in the trunk is the first to appear. The wall of the
alimentary canal becomes thickened along the median dorsal line (fig. 412,
r), or else produced into a ridge into which there penetrates a narrow
prolongation of the lumen of the alimentary canal. In either case the cells
at the extreme summit become gradually constricted off as a rod, which lies
immediately dorsal to the alimentary tract, and ventral to the notochord
(fig. 413, *).
 
 
 
 
 
FIG. 412. TRANSVERSE SECTION
THROUGH THE TAIL REGION OF A
PRISTIURUS EMBRYO OF THE SAME
AGE AS FIG. 28 E.
 
df. dorsal fin ; sp.c. spinal cord ;
//. body cavity ; sp. splanchnic layer
of mesoblast ; so. somatic layer of
mesoblast; mp'. portion of splanchnic
mesoblast commencing to be differentiated into muscles ; ch. notochord ; x.
subnotochordal rod arising as an outgrowth of the dorsal wall of the alimentary tract ; al. alimentary tract.
 
 
 
FIG. 413. TRANSVERSE SECTION THROUGH THE TRUNK OF AN
EMBRYO SLIGHTLY OLDER THAN
FIG. 28 E.
 
nc. neural canal ; pr. posterior
root of spinal nerve; x. subnotochordal rod; ao. aorta; sc. somatic
mesoblast; sp. splanchnic mesoblast; mp. muscle-plate; mp'. portion of muscle-plate converted into
muscle ; Vv. portion of the vertebral
plate which will give rise to the vertebral bodies ; al. alimentary tract.
 
 
 
In the hindermost part of the body its mode of formation differs somewhat from that above described. In this part the alimentary wall is' very
thick, and undergoes no special growth prior to the formation of the subnotochordal rod ; on the contrary, a small linear portion of the wall becomes
scooped out along the median dorsal line, and eventually separates from the
remainder as the rod in question. In the trunk the splitting off of the rod
takes place from before backwards, so that the anterior part of it is formed
before the posterior.
 
The section of the subnotochordal rod in the head would appear to
develop in the same way as that in the trunk, and the splitting off from the
throat proceeds from before backwards.
 
482
 
 
 
756 MESENTERY.
 
 
 
On the formation of the dorsal aorta, the subnotochordal rod becomes
separated from the wall of the gut and the aorta interposed between the two
(fig. 367, *).
 
When the subnotochordal rod attains its fullest development it terminates
anteriorly some way in front of the auditory vesicle, though a little behind
the end of the notochord ; posteriorly it extends very nearly to the extremity
of the tail and is almost co-extensive with the postanal section of the
alimentary tract, though it does not reach quite so far back as the caudal
vesicle (fig. 424, b x). Very shortly after it has attained its maximum size it
begins to atrophy in front. We may therefore conclude that its atrophy,
like its development, takes place from before backwards. During the later
embryonic stages not a trace of it is to be seen. It has also been met with
in Acipenser, Lepidosteus, the Teleostei, Petromyzon, and the Amphibia, in
all of which it appears to develop in fundamentally the same way as in
Elasmobranchii. In Acipenser it appears to persist in the adult as the
subvertebral ligament (Bridge, Salensky). It has not yet been found in a
fully developed form in any amniotic Vertebrate, though a thickening of the
hypoblast, which may perhaps be a rudiment of it, has been found by
Marshall and myself in the Chick (fig. 1 10, x).
 
Eisig has instituted an interesting comparison between it and an organ
which he has found in a family of Chaetopods, the Capitellidas. In these
forms there is a tube underlying the alimentary tract for nearly its whole
length, and opening into it in front, and probably behind. A remnant of
such a tube might easily form a rudiment like the subnotochordal rod of the
Ichthyopsida, and as Eisig points out the prolongation into the latter during
its formation of the lumen of the alimentary tract distinctly favours such a
view of its original nature. We can however hardly suppose that there is
any direct genetic connection between Eisig's organ in the Capitellidas and
the subnotochordal rod of the Chordata.
 
 
 
Splanchnic mesoblast and mesentery- The mesentcron
consists at first of a simple hypoblastic tube, which however
becomes enveloped by a layer of splanchnic mesoblast. This
layer, which is not at first continued over the dorsal side of the
mesenteron, gradually grows in, and interposes itself between the
hypoblast of the mesenteron, and the organs above. At the same
time it becomes differentiated into two layers, viz. an outer
cpithelioid layer which gives rise to part of the peritoneal
epithelium, and an inner layer of undifferentiated cells which in
time becomes converted into the connective tissue and muscular
walls of the mesenteron. The connective tissue layers become
first formed, while of the muscular layers the circular is the first
to make its appearance.
 
 
 
ALIMENTARY CANAL. 757
 
Coincidently with their differentiation the connective tissuestratum of the peritoneum becomes established.
 
The Mesentery. Prior to the splanchnic mesoblast growing
round the alimentary tube above, the attachment of the latter
structure to the dorsal wall of the body is very wide. On the
completion of this investment the layer of mesoblast suspending
the alimentary tract becomes thinner, and at the same time the
alimentary canal appears to be drawn downwards and away from
the vertebral column.
 
In what may be regarded as the thoracic division of the general
pleuroperitoneal space, along that part of the alimentary canal
which will form the oesophagus, this withdrawal is very slight, but
it is very marked in the abdominal region. In the latter the at
first straight digestive canal comes to be suspended from the body
above by a narrow flattened band of mesoblastic tissue. This
flattened band is the mesentery, shewn commencing in fig. 117,
and much more advanced in fig. 1 19, M. It is covered on either
side by a layer of flat cells, which form part of the general
peritoneal epithelioid lining, while its interior is composed of
indifferent tissue.
 
The primitive simplicity in the arrangement of the mesentery
is usually afterwards replaced by a more complicated disposition,
owing to the subsequent elongation and consequent convolution
of the intestine and stomach.
 
The layer of peritoneal epithelium on the ventral side of the
stomach is continued over the liver, and after embracing the liver,
becomes attached to the ventral abdominal wall (fig. 380). Thus
in the region of the liver the body cavity is divided into two
halves by a membrane, the two sides of which are covered by the
peritoneal epithelium, and which encloses the stomach dorsally
and the liver ventrally. The part of the membrane between the
stomach and liver is narrow, and constitutes a kind of mesentery
suspending the liver from the stomach : it is known to human
anatomists as the lesser omentum.
 
The part of the membrane connecting the liver with the
anterior abdominal wall constitutes the fa lei form or suspensory ligament of the liver. It arises by a secondary fusion, and
is not a remnant of a primitive ventral mesentery (vide pp. 624
and 625).
 
 
 
758 MESENTERY.
 
 
 
The mesentery of the stomach, or mesogastrium, enlarges in
Mammalia to form a peculiar sack known as the greater
omentum.
 
The mesenteron exhibits very early a trifold division. An
anterior portion, extending as far as the stomach, becomes
separated off as the respiratory division. On the formation
of the anal invagination the portion of the mesenteron behind
the anus becomes marked off as the postanal division, and
between the postanal section and the respiratory division is a
middle portion forming an intestinal and cloacal division.
 
The respiratory division of the mesenteron.
 
This section of the alimentary canal is distinguished by the
fact that its walls send out a series of paired diverticula, which
meet the skin, and after a perforation has been effected at the
regions of contact, form the branchial or visceral clefts.
 
In Amphioxus the respiratory region extends close up to the
opening of the hepatic diverticulum, and therefore to a position
corresponding with the commencement of the intestine in higher
types. In the craniate Vertebrata the number of visceral clefts
has become reduced, but from the extension of the visceral clefts
in Amphioxus, combined with the fact that in the higher Vertebrata the vagus nerve, which is essentially the nerve of the
branchial pouches, supplies in addition the walls of the oesophagus
and stomach, it may reasonably be concluded, as has been pointed
out by Gegenbaur, that the true respiratory region primitively
included the region which in the higher types forms the
oesophagus and stomach.
 
In Ascidians the respiratory sack is homologous with the
respiratory tract of Amphioxus.
 
The details of the development of the branchial clefts in the
different groups of Vertebrata have already been described in
the systematic part of this work.
 
In all the Ichthyopsida the walls of a certain number of
clefts become folded ; and in the mesoblast within these folds a
rich capillary network, receiving its blood from the branchial
arteries, becomes established. These folds constitute the true
internal gills.
 
 
 
ALIMENTARY CANAL.
 
 
 
759
 
 
 
In addition to internal gills external branchial processes covered
by epiblast are placed on certain of the visceral arches in the
larva of Polypterus, Protopterus and many Amphibia. The
external gills have probably no genetic connection with the
internal gills.
 
The so-called external gills of the embryos of Elasmobranchii
are merely internal gills prolonged outwards through the gill
clefts.
 
The posterior part of the primitive respiratory division of the
mesenteron becomes, in all the higher Vertebrata, the oesophagus
and stomach. With reference to the development of these parts
the only point worth especially noting is the fact that in
Elasmobranchii and Teleostei their lumen, though present in
very young embryos, becomes at a later stage completely filled
up, and thus the alimentary tract in the regions of the
oesophagus and stomach becomes a solid cord of cells (fig. 23
A, ces)\ as already suggested (p. 61) it seems not impossible that
this feature may be connected with the fact that the cesophageal
region of the throat was at one time perforated by gill clefts.
 
In addition to the gills two important organs, viz. the
thyroid body and the lungs, take their origin from the respiratory region of the alimentary tract.
 
Thyroid body. In the Ascidians the origin of a groovelike diverticulum of the ventral wall of the branchial sack,
bounded by two lateral folds, and known as the endostyle or
hypopharyngeal groove, has already been described (p. 18).
This groove remains permanently open to the pharyngeal sack,
 
 
 
 
FIG. 414. DIAGRAMMATIC VERTICAL SECTION OF A JUST-HATCHED LARVA
 
OF PETROMYZON. (From Gegenbaur ; after Calberla.)
 
o. mouth ; 6. olfactory pit ; v. septum between stomodteum and mesenteron ;
h. thyroid involution ; n. spinal cord ; ch. notochord; c. heart ; a. auditory vesicle.
 
 
 
760
 
 
 
THE THYROID BODY.
 
 
 
 
and would seem to serve as a glandular organ secreting mucus.
As was first pointed out by W. Miiller there is present in
Amphioxus a very similar and probably homologous organ,
known as the hypopharyngeal groove.
 
In the higher Vertebrata this organ never retains its primitive condition in the adult state. In the larva of Petromyzon
there is, however, present a ventral groove-like diverticulum of
the throat, extending from about the second to the fourth
visceral cleft. This organ is shewn in longitudinal section in
fig. 414, h, and in transverse section in fig. 415, and has been
identified by W. Muller (Nos. 565 and 566) with the hypopharyngeal groove of Amphioxus and Ascidians. It does
not, however, long retain its
primitive condition, but its opening becomes gradually reduced
to a pore, placed between the
third and fourth of the permanent clefts (fig. 416, tli). This
opening is retained throughout
the Ammoccete condition, but
the organ becomes highly complicated, with paired anterior
and posterior horns and a
median spiral portion. In the adult the connection with the
pharynx is obliterated, and the organ is partly absorbed and
partly divided up into a series of glandular follicles, and eventually forms the thyroid body.
 
From the consideration of the above facts W. Muller was led
to the conclusion tJiat the tJiyroid body of the Craniata was
derived from the endostyle or Jiypopharyngeal groove. In all the
higher Vertebrata the thyroid body arises as a diverticulum of
the ventral wall of the throat in the region either of the mandibular or hyoid arches (fig. 417, Tk}, which after being segmented
off becomes divided up into follicles.
 
In Elasmobranch embryos it appears fairly early as a diverticulum from
the ventral surface of the throat in the region of the niandibular arc/i,
extending from the border of the mouth to the point where the ventral aorta
divides into the two aortic branches of the mandibular arch (fig. 417, Th}.
 
 
 
FIG. 415. DIAGRAMMATIC TRANSVERSE SECTIONS THROUGH THE BRANCHIAL REGION OF YOUNG LARV.K OF
PETROMYZON. (From Gegenbaur ; after
Calberla.)
 
d. branchial region of throat.
 
 
 
ALIMENTARY CANAL.
 
 
 
761
 
 
 
Somewhat later it becomes in Scyllium and Torpedo solid, though still
retaining its attachment to the wall of the oesophagus. It continues to grow
in length, and becomes divided up into a number of solid branched lobules
separated by connective tissue septa. Eventually its connection with the
throat becomes lost, and the lobules develop a lumen. In Acanthias the
lumen of the gland is retained (W. Miiller) till after its detachment from the
 
 
 
-- "
 
 
Pti
 
 
 
 
FIG. 416. DIAGRAMMATIC VERTICAL SECTION THROUGH THE HEAD OF A
LARVA OF PETROMYZON.
 
The larva had been hatched three days, and was 4 '8 mm. in length. The optic
and auditory vesicles are supposed to be seen through the tissues. The letter tv
pointing to the base of the velum is where Scott believes the hyomandibular cleft to
be situated.
 
c.h. cerebral hemisphere ; th. optic thalamus; in. infundibulum ; pn. pineal gland ;
mb. mid-brain ; cb, cerebellum ; md. medulla oblongata ; au.v. auditory vesicle ; op.
optic vesicle; ol. olfactory pit; m. mouth; br.c. branchial pouches; th. thyroid
involution; v.ao. ventral aorta; ht. ventricle of heart ; ch. notochord.
 
throat. It preserves its embryonic position through life. In Amphibia it
originates, as in Elasmobranchii, from the region of the mandibular arch ;
but when first visible it forms a double epithelial wall connecting the throat
with the nervous layer of the epidermis. It subsequently becomes detached
from the epidermis, and then has the usual form of a diverticulum from the
throat. In most Amphibians it becomes divided into two lobes, and so
forms a paired body. The peculiar connection between the thyroid diverticulum and the epidermis in Amphibia has been noted by Gotte in
Bombinator, and by Scott and Osborn in Triton. It is not very easy to see
what meaning this connection can have.
 
In the Fowl (W. Miiller) the thyroid body arises at the end of the second
or beginning of the third day as an outgrowth from the hypoblast of the
throat, opposite the point of origin of the anterior arterial arch. This
outgrowth becomes by the fourth day a solid mass of cells, and by the fifth
ceases to be connected with the epithelium of the throat, becoming at the
same time bilobed. By the seventh day it has travelled somewhat backwards, and the two lobes have completely separated from each other. By
 
 
 
762
 
 
 
THE THYROID BODY.
 
 
 
the ninth day the whole is invested by a
capsule of connective tissue, which sends
in septa dividing it into a number of lobes
or solid masses of cells, and by the sixteenth day it is a paired body composed of
a number of hollow branched follicles, each
with a ' membrana propria,' and separated
from each other by septa of connective
tissue. It finally travels back to the point
of origin of the carotids.
 
Amongst Mammalia the thyroid arises
in the Rabbit (Kolliker) and Man (His) as
a hollow diverticulum of the throat at the
bifurcation of the foremost pair of aortic
arches. It soon however becomes solid,
and is eventually detached from the throat
and comes to lie on the ventral side of the
larynx or windpipe. The changes it undergoes are in the main similar to those in the
lower Vertebrata. It becomes partially
constricted into two lobes, which remain
however united by an isthmus 1 . The fact
that the thyroid sometimes arises in the
region of the first and sometimes in that of
the second cleft is probably to be explained
 
 
 
 
Tli
 
 
 
FIG. 417. SECTION THROUGH
THE HEAD OF AN ELASMOBRANCH
EMBRYO, AT THE LEVEL OF THE
AUDITORY INVOLUTION.
 
Th. rudiment of thyroid body ;
aup. auditory pit ; aim. ganglion
of auditory nerve ; iv. v. roof of
fourth ventricle ; a.c.v. anterior
cardinal vein ; aa. aorta ; f.aa
aortic trunk of mandibular arch ;
//. head cavity of mandibular
arch ; Ivc. alimentary pouch which
will form the first visceral cleft.
 
 
 
by its rudimentary character.
 
The Thymus gland. The thymus gland may conveniently be
dealt with here, although its origin is nearly as obscure as its function. It
has usually been held to be connected with the lymphatic system. Kolliker
was the first to shew that this view was probably erroneous, and he
attempted to prove that it was derived in the Rabbit from the walls of one
of the visceral clefts, mainly on the ground of its presenting in the embryo
an epithelial character.
 
1 Wolfler (No. 571) states that in the Pig and Calf the thyroid body is formed as a
pair of epithelial vesicles, which are developed as outgrowths of the walls of the first
pair of visceral clefts. He attempts to explain the contradictory observations of other
embryologists by supposing that they have mistaken the ventral ends of visceral
pouches for an unpaired outgrowth of the throat. Stieda (No. 569) also states that in
the Pig and Sheep the thyroid arises as a paired body from the epithelium of a pair
of visceral clefts, at a much later period than would appear from the observations of
His and Kolliker. In view of the comparative development of this organ it is
difficult to accept either Wolfler's or Stieda's account. Wolfler's attempt to explain
the supposed errors of his predecessors is certainly not capable of being applied in
the case of Elasmobranch Fishes, or of Petromyzon ; and I am inclined to think that
the method of investigation by transverse sections, which has been usually employed,
is less liable to error than that by longitudinal sections which he has adopted.
 
 
 
ALIMENTARY CANAL. 763
 
 
 
Stieda (No. 569) has recently verified Kolliker's statements. He finds
that in the Pig and the Sheep the thymus arises as a paired outgrowth from
the epithelial remnants of a pair of visceral clefts. Its two lobes may at first
be either hollow (Sheep) or solid (Pig), but eventually become solid, and
unite in the median line. Stieda and His hold that in the adult gland, the
so-called corpuscles of Hassall are the remnants of the embryonic epithelial
part of the gland, and that the lymphatic part of it is of mesoblastic origin ;
but Kolliker believes the lymphatic cells to be direct products of the
embryonic epithelial cells.
 
The posterior visceral clefts in the course of their atrophy give rise to
various more or less conspicuous bodies of a pseudo-glandular nature, which
have been chiefly studied by Remak 1 .
 
Swimming bladder and lungs. A swimming bladder is
present in all Ganoids and in the vast majority of Teleostei.
Its development however is only imperfectly known.
 
In the Salmon and Carp it arises, as was first shewn by Von
Baer, as an outgrowth of the alimentary tract, shortly in front of
the liver. In these forms it is at first placed on the dorsal side
and slightly to the right, and grows backwards on the dorsal
side of the gut, between the two folds of the mesentery.
 
The absence of a pneumatic duct in the Physoclisti would
appear to be due to a post-larval atrophy.
 
In Lepidosteus the air-bladder appears to arise, as in the
Teleostei, as an invagination of the dorsal wall of the oesophagus.
 
In advanced embryos of Galeus, Mustelus and Acanthias, MikluchoMaclay detected a small diverticulum opening on the dorsal side of the
oesophagus, which he regards as a rudiment of a swimming bladder. This
interpretation must however be regarded as somewhat doubtful.
 
The lungs. The lungs originate in a nearly identical way in
all the Vertebrate forms in which their development has been
observed. They are essentially buds or processes of the ventral
wall of the primitive oesophagus.
 
At a point immediately behind the region of the visceral
clefts the cavity of the alimentary canal becomes compressed
laterally, and at the same time constricted in the middle, so that
its transverse section (fig. 418 i) is somewhat hourglass-shaped,
and shews an upper or dorsal chamber d, joining on to a lower
or ventral chamber / by a short narrow neck.
 
1 For details on these organs vide Kolliker, Entwicklungsgeschichte, p. 88 1.
 
 
 
764
 
 
 
THE LUNGS.
 
 
 
 
The hinder end of the lower tube enlarges (fig. 418 2), and
then becomes partially divided into two lobes (fig. 418 3). All
these parts at first freely communicate, but the two lobes,
partly by their own growth,
and partly by a process of constriction, soon become isolated
posteriorly; while in front they
open into the lower chamber
of the oesophagus (fig. 422).
 
By a continuation forwards
of the process of constriction
the lower chamber of the oesophagus, carrying with it the
two lobes above mentioned,
becomes gradually transformed
into an independent tube,
opening in front by a narrow
slit-like aperture into the oesophagus. The single tube in
front is the rudiment of the
trachea and larynx, while the
two diverticula behind become
(fig. 419, Ig) the bronchial tubes
and lungs.
 
While the above changes
are taking place in the hypoblastic walls of the alimentary
tract, the splanchnic mesoblast
surrounding these structures
becomes very much thickened ; but otherwise bears no marks of
the internal changes which are going on, so that the above
formation of the lungs and trachea cannot be seen from the
surface. As the paired diverticula of the lungs grow backwards,
the mesoblast around them takes however the form of two lobes,
into which they gradually bore their way.
 
There do not seem to be any essential differences in the mode of
formation of the above structures in the types so far observed, viz. Amphibia,
Aves and Mammalia. Writers differ as to whether the lungs first arise as
 
 
 
FlG. 418. FOUR DIAGRAMS ILLUSTRATING THE FORMATION OF THE LUNGS.
 
(After Gotte.)
 
a. mesoblast; b. hypoblast; d. cavity
of digestive canal ; /. cavity of the pulmonary diverticulum.
 
In (i) the digestive canal has commenced to be constricted into an upper
and lower canal ; the former the true
alimentary canal, the latter the pulmonary tube; the two tubes communicate
with each other in the centre.
 
In (2) the lower (pulmonary) tube has
become expanded.
 
In (3) the expanded portion of the
tube has become constricted into two
tubes, still communicating with each other
and with the digestive canal.
 
In (4) these are completely separated
from each other and from the digestive
canal, and the mesoblast has also begun
to exhibit externally changes corresponding to the internal changes which have
been going on.
 
 
 
ALIMENTARY CANAL.
 
 
 
765
 
 
 
re
 
 
 
paired diverticula, or as a single diverticulum ; and as to whether the
rudiments of the lungs are established
before those of the trachea. If the above
account is correct it would appear that
any of these positions might be maintained. Phylogenetically interpreted the
ontogeny of the lungs appears however
to imply that this organ was first an
unpaired structure and has become
secondarily paired, and that the trachea
was relatively late in appearing.
 
The further development of the
lungs is at first, in the higher types
at any rate, essentially similar to
that of a racemose gland. From
each primitive diverticulum numerous branches are given off
In Aves and Mammalia (fig. 355)
they are mainly confined to the
dorsal and lateral parts. These
branches penetrate into the surrounding mesoblast and continue
to give rise to secondary and
tertiary branches. In the meso
 
 
 
At
 
 
 
FIG. 419. SECTION THROUGH
THE CARDIAC REGION OF AN EMBRYO
OF LACERTA MURALIS OF 9 MM. TO
SHEW THE MODE OF FORMATION OF
THE PERICARDIAL CAVITY.
 
ht. heart ; pc . pericardial cavity ;
al. alimentary tract; Ig. lung; /.
liver; pp. body cavity; md. open
end of Mullerian duct; wd. Wolffian
duct ; vc. vena cava inferior ; ao.
aorta; ch. notochord; me, medullary
cord.
 
 
 
blast around them numerous capillaries make their appearance, and the further growth of the
bronchial tubes is supposed by Boll to be due to the mutual
interaction of the hitherto passive mesoblast and of the hypoblast.
 
The further changes in the lungs vary somewhat in the different forms.
 
The air sacks are the most characteristic structures of the avian lung.
They are essentially the dilated ends of the primitive diverticula or of their
main branches.
 
In Mammalia (Kolliker, No. 298) the ends of the bronchial tubes become
dilated into vesicles, which may be called the primary air-cells. At first,
owing to their development at the ends of the bronchial branches, these are
confined to the surface of the lungs. At a later period the primary air-cells
divide each into two or three parts, and give rise to secondary air-cells, while
at the same time the smallest bronchial tubes, which continue all the while
to divide, give rise at all points to fresh air-cells. Finally the bronchial
tubes cease to become more branched, and the air-cells belonging to each
minute lobe come in their further growth to open into a common chamber.
 
 
 
766 THE CLOACA.
 
 
 
Before the lungs assume their function the embryonic air-cells undergo a
considerable dilatation.
 
The trachea and larynx. The development of the trachea and larynx
does not require any detailed description. The larynx is formed as a simple
dilatation of the trachea. The cartilaginous structures of the larynx are of
the same nature as those of the trachea.
 
It follows from the above account that the whole pulmonary
structure is the result of the growth by budding of a system of
branched hypoblastic tubes in the midst of a mass of mesoblastic
tissue, the hypoblastic elements giving rise to the epithelium of
the tubes, and the mesoblast providing the elastic, muscular,
cartilaginous, vascular, and other connective tissues of the
tracheal and bronchial walls.
 
There can be no doubt that the lungs and air-bladder are
homologous structures, and the very interesting memoir of Eisig
on the air-bladder of the Chaetopoda 1 shews it to be highly
probable that they are the divergent modifications of a primitive
organ, which served as a reservoir for gas secreted in the
alimentary tract, the gas in question being probably employed
for respiration when, for any reason, ordinary respiration by the
gills was insufficient.
 
Such an organ might easily become either purely respiratory,
receiving its air from the exterior, and so form a true lung ; or
mainly hydrostatic, forming an air-bladder, as in Ganoidei and
Teleostei.
 
It is probable that in the Elasmobranchii the air-bladder has
become aborted, and the organ discovered by Micklucho-Maclay
may perhaps be a last remnant of it.
 
The middle division of the mesenteron. The middle
division of the mesenteron, forming the intestinal and cloacal
region, is primitively a straight tube, the intestinal region of
which in most Vertebrate embryos is open below to the yolksack.
 
Cloaca. In the Elasmobranchii, the embryos of which
probably retain a very primitive condition of the mesenteron,
this region is not at first sharply separated from the postanal
section behind. Opposite the point where the anus will even
1 H. Eisig, " Ueb. d. Vorkommen eines schwimmblasenahnlichen Organs bei
Anneliden." Mittheil. a. d. zool. Station z. Neafel, Vol. II. 1881.
 
 
 
ALIMENTARY CANAL.
 
 
 
767
 
 
 
tually appear a dilatation of the mesenteron arises, which comes
in contact with the external skin (fig. 28 E, an}. This dilatation
becomes the hypoblastic section of the cloaca. It communicates
behind with the postanal gut (fig. 424 D), and in front with the
intestine ; and may be defined as the dilated portion of the alimentary tract which receives the genital and urinary ducts and opens
externally by the proctodczum.
 
In Acipenser and Amphibia the cloacal region is indicated
as a ventral diverticulum of the mesenteron even before the
closure of the blastopore. It is shewn in the Amphibia at an
early stage in fig. 73, and at a later period, when in contact with
the skin at the point where the anal invagination is about to
appear, in fig. 420.
 
 
 
 
FIG. 420. LONGITUDINAL SECTION THROUGH AN ADVANCED EMBRYO OF
 
BOMBINATOR. (After Gotte.)
 
m. mouth ; an. anus ; /. liver ; ne. neurenteric canal ; me. medullary canal ; ch.
notochord ; pn. pineal gland.
 
In the Sauropsida and Mammalia the cloaca appears as a
dilatation of the mesenteron, which receives the opening of the
allantois almost as soon as the posterior part of the mesenteron
is established.
 
The eventual changes which it undergoes have been already
dealt with in connection with the urinogenital organs.
 
Intestine. The region in front of the cloaca forms the
intestine. In certain Vertebrata it nearly retains its primitive
character as a straight tube ; and in these types its anterior
part is characterised by the presence of a peculiar fold, which in
a highly specialised condition is known as the spiral valve.
This structure appears in its simplest form in Ammocoetes. It
 
 
 
768 THE INTESTINE.
 
 
 
there consists of a fold in the wall of the intestine, giving to the
lumen of this canal a semilunar form in section, and taking a
half spiral.
 
In Elasmobranchii a similar fold to that in Ammoccetes first
makes its appearance in the embryo. This fold is from the
first not quite straight, but winds in a long spiral round the
intestine. In the course of development it becomes converted
into a strong ridge projecting into the lumen of the intestine
(fig. 388, /). The spiral it makes becomes much closer, and it
thus acquires the form of the adult spiral valve. A spiral valve
is also found in Chimaera and Ganoids. No rudiment of such
an organ is found in the Teleostei, the Amphibia, or the higher
Vertebrata.
 
The presence of this peculiar organ appears to be a very
primitive Vertebrate character. The intestine of Ascidians
exhibits exactly the same peculiarity as that of Ammoccetes,
and we may probably conclude from embryology that the
ancestral Chordata were provided with a straight intestine
having a fold projecting into its lumen, to increase the area of
the intestinal epithelium.
 
In all forms in which there is not a spiral valve, with the
exception of a few Teleostei, the intestine becomes considerably
longer than the cavity which contains it, and therefore necessarily more or less convoluted.
 
The posterior part usually becomes considerably enlarged to
form the rectum or in Mammalia the large intestine.
 
In Elasmobranchii there is a peculiar gland opening into the
dorsal side of the rectum, and in many other forms there is a
caecum at the commencement of the rectum or of the large
intestine.
 
In Teleostei, the Sturgeon and Lepidosteus there opens into
the front end of the intestine a number of caecal pouches known
as the pancreatic caeca. In the adult Sturgeon these pouches
unite to form a compact gland, but in the embryo they arise as
a series of isolated outgrowths of the duodenum.
 
Connected with the anterior portion of the middle region of
the alimentary canal, which may be called the duodenum, are
two very important and constant glandular organs, the liver and
the pancreas.
 
 
 
ALIMENTARY CANAL.
 
 
 
769
 
 
 
ITlf
 
 
 
 
The liver. The liver is the earliest formed and largest
glandular organ in the embryo.
 
It appears in its simplest
form in Amphioxus as a single
unbranched diverticulum of the
alimentary tract, immediately
behind the respiratory region,
which is directed forwards and
placed on the left side of the
body.
 
In all true Vertebrata the
gland has a much more complicated structure. It arises as a
ventral outgrowth of the duodenum (fig. 420, /). This outgrowth may be at first single,
and then grow out into two
lobes, as in Elasmobranchii (fig.
421) and Amphibia, or have from
the first the form of two somewhat unequal diverticula, as in
Birds (fig. 422), or again as in
the Rabbit (Kolliker) one diverticulum may be first formed, and a second one appear
somewhat later. The hepatic diverticula, whatever may be
their primitive form, grow into a special thickening of the
splanchnic mesoblast.
 
From the primitive diverticula there are soon given off a
number of hollow buds (fig. 421) which rapidly increase in
length and number, and form the so-called hepatic cylinders.
They soon anastomose and unite together, and so constitute an
irregular network. Coincidently with the formation of the
hepatic network the united vitelline and visceral vein or veins
(u.v\ in their passage through the liver, give off numerous
branches, and gradually break up into a plexus of channels
which form a secondary network amongst the hepatic cylinders.
In Amphibia these channels are stated by Gotte to be lacunar,
but in Elasmobranchii, and probably Vertebrata generally, they
arc from the first provided with distinct though delicate walls.
B. in. 49
 
 
 
FIG. 421. SECTION THROUGH THE
VENTRAL PART OF THE TRUNK OF A
YOUNG EMBRYO OF SCYLLIUM AT THE
LEVEL OF THE UMBILICAL CORD.
 
b. pectoral fin ; ao. dorsal aorta ;
cav. cardinal vein; ua. vitelline artery ; nv. vitelline vein united with
subintestinal vein ; al. duodenum ;
/. liver ; sd. opening of segmental
duct into the body-cavity ; mp. muscle-plate ; urn. umbilical canal.
 
 
 
770
 
 
 
THE LIVER.
 
 
 
It is still doubtful whether the hepatic cylinders are as a rule hollow or
solid. In Elasmobranchii they are at first provided with a large lumen,
which though it becomes gradually smaller never entirely vanishes. The
same seems to hold good for Amphibia and some Mammalia. In Aves
the lumen of the cylinders is even from the first much more difficult
to see, and the cylinders are stated by Remak to be solid, and he has
been followed in this matter by Kolliker. In the Rabbit also Kolliker finds
the cylinders to be solid.
 
The embryonic hepatic network gives rise to the parenchyma
of the adult liver, with which in
its general arrangement it closely
agrees. The blood-channels are
at first very large, and have a
very irregular arrangement ; and
it is not till comparatively late
that the hepatic lobules with their
characteristic vascular structures
become established.
 
The biliary ducts are formed
either from some of the primitive hepatic cylinders, or, as
would seem to be the case in
Elasmobranchii and Birds (fig.
422), from the larger diverticula of the two primitive outgrowths.
 
The gall-bladder is so inconstant, and the arrangement of
the ducts opening into the intestine so variable, that no general statements can be made about
them. In Elasmobranchii the primitive median diverticulum
(fig. 421) gives rise to the ductus choledochus. Its anterior end
dilates to form a gall-bladder.
 
In the Rabbit a ductus choledochus is formed by a diverticulum from the intestine at the point of insertion of the two
primitive lobes. The gall-bladder arises as a diverticulum of
the right primitive lobe.
 
The liver is relatively very large during embryonic life and
has, no doubt, important functions in connection with the circulation.
 
 
 
 
r
 
 
 
FIG. 422. DIAGRAM OF THE DIGESTIVE TRACT OF A CHICK UPON THE
FOURTH DAY. (After Gotte.)
 
The black line indicates the hypoblast. The shaded part around it is
the splanchnic mesoblast.
 
Ig. lung ; st. stomach ; p. pancreas ;
/. liver.
 
 
 
ALIMENTARY CANAL.
 
 
 
771
 
 
 
The pancreas. So far as is known the development of the
pancreas takes place on a very constant type throughout the
series of craniate Vertebrata, though absent in some of the
Teleostean fishes and Cyclostomata, and very much reduced in
most Teleostei and in Petromyzon.
 
It arises nearly at the same time as the liver in the form of a
hollow outgrowth from the dorsal side of the intestine nearly
opposite but slightly behind the hepatic outgrowth (fig. 422, /).
It soon assumes, in Elasmobranchii and Mammalia, somewhat
the form of an inverted funnel, and from the expanded dorsal
part of the funnel there grow out numerous hollow diverticula
into the passive splanchnic mesoblast.
 
As the ductules grow longer and become branched, vascular
processes grow in between them, and the whole forms a compact
glandular body in the mesentery on the dorsal side of the
alimentary tract. The funnel-shaped receptacle loses its origi nal form, and elongating, assumes the character of a duct.
 
From the above mode of development it is clear that the
glandular cells of the pancreas are derived from the hypoblast.
 
Into the origin of the varying arrangements of the pancreatic
ducts it is not possible to enter in detail. In some cases,
e.g. the Rabbit (Kolliker), the two lobes and ducts arise from a
division of the primitive gland and duct. In other cases, e.g. the
Bird, a second diverticulum springs from the alimentary tract.
In a large number of instances the primitive condition with a
single duct is retained.
 
Postanal section of the mesenteron. In the embryos of
all the Chordata there is a section of the mesenteron placed
behind the anus. This section invariably atrophies at a comparatively early period of embryonic life ; but it is much better
developed in the lower forms than in the higher. At its
posterior extremity it is primitively continuous with the neural
tube (fig. 420), as was first shewn by Kowalevsky.
 
The canal connecting the neural and alimentary canals has
already been described as the neurenteric canal, and represents
the remains of the blastopore.
 
In the Tunicata the section of the mesenteron, which in all probability
corresponds to the postanal gut of the Vertebrata, is that immediately
 
492
 
 
 
 
772 POSTANAL SECTION OF THE MESENTERON.
 
following the dilated portion which gives rise to the branchial cavity
 
and permanent intestine. It has already
 
been shewn that from the dorsal and
 
lateral portions of this section of the
 
primitive alimentary tract the notochord
 
and muscles of the Ascidian tadpole are
 
derived. The remaining part of its walls
 
forms a solid cord of cells (fig. 423, al'},
 
which either atrophies, or, according to
 
Kowalevsky, gives rise to blood-vessels.
 
In Amphioxus the postanal gut, FIG. 423. TRANSVERSE OPTICAL
 
.hough distinctly developed, is no, very %
long, and atrophies at a comparatively (After Kowalevsky.)
early period. The sect i on ; s f rom an embryo of
 
In Elasmobranchii this section of the the same age as fig. 8 iv.
 
alimentary tract is very well developed, ch - notochord ; nc neural 1 canal ;
 
. , , me. mesoblast ; of. hypoblast of
and persists for a considerable period of ta ji <
 
embryonic life. The following is a
history of its development in the genus Scyllium.
 
Shortly after the stage when the anus has become marked out by the
alimentary tract sending down a papilliform process towards the skin, the
postanal gut begins to develop a terminal dilatation or vesicle, connected
with the remainder of the canal by a narrower stalk.
 
The walls both of the vesicle and stalk are formed of a fairly columnar
epithelium. The vesicle communicates in front by a narrow passage with
the neural canal, and behind is continued into two horns corresponding
with the two caudal swellings previously spoken of (p. 55). Where the
canal is continued into these two horns, its walls lose their distinctness of
outline, and become continuous with the adjacent mesoblast.
 
In the succeeding stages, as the tail grows longer and longer, the postanal section of the alimentary tract grows with it, without however undergoing alteration in any of its essential characters. At the period of the
maximum development, it has a length of about -J of that of the whole
alimentary tract.
 
Its features at a stage shortly before the external gills have become
prominent are illustrated by a series of transverse sections through the
tail (fig. 424). The four sections have been selected for illustration out of a
fairly-complete series of about one hundred and twenty.
 
Posteriorly (A) there is present a terminal vesicle (alv) '25 mm. in
diameter, which communicates dorsally by a narrow opening with the
neural canal (nc) ; to this is attached a stalk in the form of a tube, also
lined by columnar epithelium, and extending through about thirty sections
(B al}. Its average diameter is about '084 mm., and its walls are very thick.
Overlying its front end is the subnotochordal rod (x), but this does not
extend as far back as the terminal vesicle.
 
The thick-walled stalk of the vesicle is connected with the cloacal section
 
 
 
ALIMENTARY CANAL.
 
 
 
773
 
 
 
of the alimentary tract by a very narrow thin-walled tube (C of). This for
the most part has a fairly uniform calibre, and a diameter of not more than
035 mm. Its walls are formed of flattened epithelial cells. At a point not
far from the cloaca it becomes smaller, and its diameter falls to -03 mm. In
 
 
 
 
cl.al
 
 
 
FIG. 424. FOUR SECTIONS THROUGH THE POSTANAL PART OF THE TAIL
OF AN EMBRYO OF THE SAME AGE AS FIG. 28 F.
 
A. is the posterior section.
 
nc . neural canal ; al. postanal gut ; alv. caudal vesicle of postanal gut ; x.
subnotochordal rod; mp. muscle-plate; ch. notochord; cl.al. cloaca; ao. aorta;
v.cau, caudal vein.
 
front of this point it rapidly dilates again, and, after becoming fairly wide,
opens on the dorsal side of the cloacal section of the alimentary canal just
behind the anus (D al}.
 
Very shortly after the stage to which the above figures belong, at a
point a little behind the anus, where the postanal section of the canal
was thinnest in the previous stage, it becomes solid, and a rupture here
occurs in it at a slightly later period.
 
The atrophy of this part of the alimentary tract having once commenced
proceeds rapidly. The posterior part first becomes reduced to a small
rudiment near the end of the tail. There is no longer a terminal vesicle,
nor a neurenteric canal. The portion of the postanal section of the
alimentary tract, just behind the cloaca, is for a short time represented
by a small rudiment of the dilated part which at an earlier period opened
into the cloaca.
 
In Teleostei the vesicle at the end of the tail, discovered by Kupffer,
 
 
 
774 THE STOMOD/EUM.
 
 
 
(fig- 34> hyv) is probably the equivalent of the vesicle at the end of the
postanal gut in Elasmobranchii.
 
In Petromyzon and in Amphibia there is a well-developed postanal
gut connected with a neurenteric canal which gradually atrophies. It is
shewh in the embryo of Bombinator in fig. 420.
 
Amongst the amniotic Vertebrata the postanal gut is less developed
than in the Ichthyopsida. A neurenteric canal is present for a short period
 
 
 
 
FIG. 425. DIAGRAMMATIC LONGITUDINAL SECTION THROUGH THE POSTERIOR
END OF AN EMBRYO BlRD AT THE TIME OF THE FORMATION OF THE ALLANTOIS.
 
ep. epiblast ; Sp.c. spinal canal ; ch. notochord ; n.e. neurenteric canal ; hy. hypoblast ; p.a.g, postanal gut ; pr. remains of primitive streak folded in on the ventral
side ; al. allantois ; me. splanchnic mesoblast ; an. point where anus will be formed ;
p.c. perivisceral cavity ; am. amnion ; so. somatopleure ; sp. splanchnopleure.
 
in various Birds (Gasser, etc.) and in the Lizard, but disappears very early.
There is however, as has been pointed out by Kolliker, a well-marked
postanal gut continued as a narrow tube from behind the cloaca into
the tail both in the Bird (fig. 425, p.a.g.} and Mammals (the Rabbit), but
especially in the latter. It atrophies early as in lower forms.
 
The morphological significance of the postanal gut and of the neurenteric canal has already been spoken of in Chapter xii., p. 323.
 
 
 
The anterior section of the permanent alimentary tract is
formed by an invagination of epiblast, constituting a more or
less considerable pit, with its inner wall in contact with the
blind anterior extremity of the alimentary tract.
 
In Ascidians this pit is placed on the dorsal surface (fig. 9, o),
and becomes the permanent oral cavity of these forms. In the
larva of Amphioxus it is stated to be formed unsymmetrically
 
 
 
THE STOMOD/EUM.
 
 
 
775
 
 
 
 
(vide p. 5), but further observations on its development are
required.
 
In the true Vertebrata it is always formed on the ventral
surface of the head, immediately behind the level of the forebrain (fig. 426), and is deeper in Petromyzon (fig. 416, ;) than
in any other known form.
 
From the primary buccal cavity or stomodaeum there grows
out the pituitary pit (fig. 426, pt\ the
development of which has already
been described (p. 435).
 
The wall separating the stomodaeum from the mesenteron always
becomes perforated, usually at an
early stage of development, and
though in Petromyzon the boundary
between the two cavities remains
indicated by the velum, yet in the
higher Vertebrata all trace of this
boundary is lost, and the original
limits of the primitive buccal cavity
become obliterated ; while a secondary buccal cavity, partly lined by
hypoblast and partly by epiblast,
becomes established.
 
This cavity, apart from the organs which belong to it,
presents important variations in structure. In most Pisces it
retains a fairly simple character, but in the Dipnoi its outer
boundary becomes extended so as to enclose the ventral opening of the nasal sack, which thenceforward constitutes the
posterior nares.
 
In Amphibia and Amniota the posterior nares also open well
within the boundary of the buccal cavity.
 
In the Amniota further important changes take place.
 
In the first place a plate grows inwards from each of the
superior maxillary processes (fig. 427, /), and the two plates,
meeting in the middle line, form a horizontal septum dividing
the front part of the primitive buccal cavity into a dorsal
respiratory section (), containing the opening of the posterior
nares, and a ventral cavity, forming the permanent mouth. The
 
 
 
FIG. 426. LONGITUDINAL
SECTION THROUGH THE BRAIN OF
A YOUNG PRISTIURUS EMBRYO.
 
r.unpaired rudimentofthecerebral hemispheres \pn. pineal gland ;
/w.infundibulum ; //.ingrowth from
mouth to form the pituitary body ;
mb. mid-brain ; cb. cerebellum ; ch.
notochord; al. alimentary tract;
Zaa. artery of mandibular arch.
 
 
 
THE TEETH.
 
 
 
 
two divisions thus formed open into a common cavity behind.
The horizontal septum, on the development within it of an
osseous plate, constitutes the hard palate.
 
An internasal septum (fig. 427, e) may more or less completely divide the dorsal cavity into two canals, continuous
respectively with the two nasal cavities.
 
In Mammalia a posterior prolongation of the palate, in which
an osseous plate is not formed, constitutes the soft palate.
 
The second change in the Amniota, which also takes place in
some Amphibia, is caused by the section of the mesenteron into
which the branchial pouches open,
becoming, on the atrophy of these
structures, converted into the posterior part of the buccal cavity.
 
The organs derived from the
buccal cavity are the tongue, the
various salivary glands, and the
teeth ; but the latter alone will engage our attention here.
 
The teeth. The teeth are to be
regarded as a special product of the
oral mucous membrane. It has been
shewn by Gegenbaur and Hertwig
that in their mode of development
they essentially resemble the placoid
scales of Elasmobranchii, and that the latter structures extend
in Elasmobranchii for a certain distance into the cavity of the
mouth.
 
As pointed out by Gegenbaur, the teeth are therefore to be
regarded as more or less specialised placoid scales, whose
presence in the mouth is to be explained by the fact that the
latter structure is lined by an invagination of the epidermis.
The most important developmental point of difference between
teeth and placoid scales consists in the fact, that in the case
of the former there is a special ingrowth of epiblast to
meet a connective tissue papilla which is not found in the
latter.
 
 
 
FIG. 427. DIAGRAM SHEWING THE DIVISION OF THE PRIMITIVE BUCCAL CAVITY INTO THE
RESPIRATORY SECTION ABOVE
AND THE TRUE MOUTH BELOW.
(From Gegenbaur.)
 
p. palatine plate of superior
maxillary process; m. permanent
mouth ; n. posterior part of nasal
passage; e. internasal septum.
 
 
 
Although the teeth are to be regarded as primitively epiblastic structures, they are nevertheless found in Teleostei and Ganoidei on the hyoid
 
 
 
THE STOMOD/KUM.
 
 
 
777
 
 
 
and branchial arches ; and very possibly the teeth on some other parts of
the mouth are developed in a true hypoblastic region.
 
The teeth are formed from two distinct organs, viz. an epithelial cap and
a connective tissue papilla.
 
The general mode of development, as has been more especially shewn
by the extended researches of Tomes, is practically the same for all Vertebrata, and it will be convenient to describe it as it takes place in Mammalia.
 
Along the line where the teeth are about to develop, there is formed
an epithelial ridge projecting into the subjacent connective tissue, and
derived from the innermost columnar layer of the oral epithelium. At the
points where a tooth is about to be formed this ridge undergoes special
changes. It becomes in the first place somewhat thickened by the development of a number of rounded cells in its interior ; so that it becomes
constituted of (i) an external layer of columnar cells, and (2) a central core
of rounded cells ; both of an epithelial nature. In the second place the
organ gradually assumes a dome-shaped form (fig. 428, e), and covers over a
papilla of the subepithelial connective tissue (p] which has in the meantime
been developed.
 
From the above epithelial structure, which may be called the enamel
organ, and from the papilla it covers, which
maybe spoken of as the dental papilla,
the whole tooth is developed. After these
parts have become established there is formed
round the rudiment of each tooth a special
connective tissue capsule ; known as the
dental capsule.
 
Before the dental capsule has become
definitely formed the enamel organ and the
dental papilla undergo important changes.
The rounded epithelial cells forming the core
of the enamel organ undergo a peculiar transformation into a tissue closely resembling
ordinary embryonic connective tissue, while
at the same time the epithelium adjoining
the dental papilla and covering the inner
surface of the enamel organ, acquires a somewhat different structure to the epithelium
on the outer side of the organ. Its cells
become very markedly columnar, and form
a very regular cylindrical epithelium. This
layer alone is concerned in forming the
enamel. The cells of the outer epithelial
layer of the enamel organ become somewhat
flattened, and the surface of the layer is raised into a series of short papilla?
which project into the highly vascular tissue of the dental sheath. Between
 
 
 
 
FIG. 428. DIAGRAM SHEWING THE DEVELOPMENT OF THE
TEETH. (From Gegenbaur.)
 
p. dental papilla ; e. enamel
organ.
 
 
 
778 THE PROCTOD/EUM.
 
the epithelium of the enamel organ and the adjoining connective tissue
there is everywhere present a delicate membrane known as the membrana
praeformativa.
 
The dental papilla is formed of a highly vascular core and a non-vascular
superficial layer adjoining the inner epithelium of the enamel organ. The
cells of the superficial layer are arranged so as almost to resemble an
epithelium.
 
The first formation of the hard structures of the tooth commences at
the apex of the dental papilla. A calcification of the outermost layer of
the papilla sets in, and results in the formation of a thin layer of dentine.
Nearly simultaneously a thin layer of enamel is deposited over this,
from the inner epithelial layer of the enamel organ (fig. 428). Both
enamel and dentine continue to be deposited till the crown of the tooth has
reached its final form, and in the course of this process the enamel
organ is reduced to a thin layer, and the whole of the outer layer of the
dental papilla is transformed into dentine while the inner portion remains
as the pulp.
 
The root of the tooth is formed later than the crown, but the enamel
organ is not prolonged over this part, so that it is only formed of dentine.
 
By the formation of the root the crown of the tooth becomes pushed
outwards, and breaking through its sack projects freely on the surface.
 
The part of the sack which surrounds the root of the tooth gives rise
to the cement, and becomes itself converted into the periosteum of the
dental alveolus.
 
The general development of the enamel organs and dental papillae is
shewn in the diagram (fig. 428). From the epithelial ridge three enamel
organs are represented as being developed. Such an arrangement may
occur when teeth are successively replaced. The lowest and youngest
enamel organ (e) has assumed a cap-like form enveloping a dental papilla,
but no calcification has yet taken place.
 
In the next stage a cap of dentine has become formed, while in the
still older tooth this has become covered by a layer of enamel. As may be
gathered from this diagram, the primitive epithelial ridge from which the
enamel organ is formed is not necessarily absorbed on the formation of a
tooth, but is capable of giving rise to fresh enamel organs. When the
enamel organ has reached a certain stage of development, its connection
with the epithelial ridge is ruptured (fig. 428).
 
The arrangement represented in fig. 428, in which successive enamel
organs are formed from the same epithelial ridge, is found in most Vertebrata except the Teleostei. In the Teleostei, however (Tomes), a fresh
enamel organ grows inwards from the epithelium for each successively
formed tooth.
 
The Proctodceuni.
 
In all Vertebrata the cloacal section of the alimentary tract
which receives the urinogenital ducts is placed in communication
 
 
 
THE PROCTOD/EUM.
 
 
 
779
 
 
 
with the exterior by means of an epiblastic invagination, constituting a proctodseum.
 
This invagination is not usually very deep, and in most
instances the boundary wall between it and the hypoblastic
cloaca is not perforated till considerably after the perforation of the
stomodseum ; in Petromyzon, however, its perforation is effected
before the mouth and pharynx are placed in communication.
 
The mode of formation of the proctodaeum, which is in
general extremely simple, is illustrated by fig. 420 an.
 
In most forms the original boundary between the cpiblast of
the proctodaeum and the hypoblast of the primitive cloaca
becomes obliterated after the two have become placed in free
communication.
 
 
 
 
FIG. 429. DIAGRAMMATIC LONGITUDINAL SECTION THROUGH THE POSTERIOR
END OF AN EMBRYO BlRD AT THE TIME OF THE FORMATION OF THE ALLANTOIS.
 
ep. epiblast ; Sp.c. spinal canal ; ch. notochord ; n.e. neurenteric canal ; hy, hypoblast ; p.a.g. postanal gut ; pr. remains of primitive streak folded in on the ventral
side ; al. allantois ; me. mesoblast ; an. point where anus will be formed ; p.c. perivisceral cavity ; am. amnion ; so. somatopleure ; sp. splanchnopleure.
 
In Birds the formation of the proctodseum is somewhat more complicated than in other types, owing to the outgrowth from it of the bursa
Fabricii.
 
The proctodseum first appears when the folding off of the tail end of
the embryo commences (fig. 429, an} and is placed near the front (originally
the apparent hind) end of the primitive streak. Its position marks out the
front border of the postanal section of the gut.
 
The bursa Fabricii first appears on the seventh day (in the chick), as a
dorsal outgrowth of the proctodaeum. The actual perforation of the septum between the proctodeeum and the cloacal section of the alimentary tract
is not effected till about the fifteenth day of fcetal life, and the approxi
 
 
780 BIBLIOGRAPHY.
 
 
 
mation of the epithelial layers of the two organs, preparatory to their
absorption, is partly effected by the tunneling of the mesoblastic tissue
between them by numerous spaces.
 
The hypoblastic section of the cloaca of birds, which receives the openings of the urinogenital ducts, is permanently marked off by a fold from
the epiblastic section or true proctodaeum, with which the bursa Fabricii
communicates.
 
BIBLIOGRAPHY.
Alimentary Canal and its appendages.
 
(561) B. Afanassiew. "Ueber Bau u. Entwicklung d. Thymus d. Saugeth."
Archivf. mikr. Anat. Bd. xiv. 1877.
 
(562) Fr. Boll. Das Princip d. Wachsthums. Berlin, 1876.
 
(563) E. Gasser. "Die Entstehung d. Cloakenoffnung bei Hiihnerembryonen."
Archivf. Anat. u. Physiol., Anat. Abth. 1880.
 
(564) A. Gotte. Beilrdge zur Entivicklungsgeschichle d. Darmkanah im
Hiihnchen. 1867.
 
(565) W. Millie r. "Ueber die Entwickelung der Schilddriise." Jenaische
Zeitschrift, Vol. vi. 1871.
 
(566) W. Miiller. "Die Hypobranchialrinne d. Tunicaten." Jenaische Zeitschrift, Vol. VII. 1872.
 
(567) S. L. Schenk. "Die Bauchspeicheldriise d. Embryo." Anatomischphysiologische Untcrsuchungen. 1872.
 
(568) E. Selenka. " Beitrag zur Entwicklungsgeschichte d. Luftsacke d.
Huhns." Zeit.f. wiss. Zool. 1866.
 
(569) L. Stieda. Untersuch. iib. d. Entwick. d. Glandula Thymus, Glandula
thyroidea,u. Glandula car otica. Leipzig, 1881.
 
(570) C. Fr. Wolff. " De formatione intestinorum." Nov. Comment. Akad.
Petrop. 1766.
 
(571) H. Wolfler. Ueb. d. Entwick. u. d. Bau d. Schilddriise. Berlin, 1880.
Vide also Kolliker (298), Gotte (296), His (232 and 297), Foster and Balfour (295),
 
Balfour (292), Remak (302), Schenk (303), etc.
 
Teeth.
 
(572) T. H. Huxley. "On the enamel and dentine of teeth." Quart. J. of
Micros. Science, Vol. in. 1855.
 
(573) R. Owen. Odontography . London, 1840 1845.
 
(574) Ch. S. Tomes. Manual of dental anatomy, human and comparative.
London, 1876.
 
(575) Ch. S. Tomes. " On the development of teeth." Quart. J. of Micros.
Science, Vol. xvi. 1876.
 
(576) W. Waldeyer. " Structure and development of teeth." Strieker's Histology. 1870.
 
Vide also Kolliker (298), Gegenbaur (294), Hertwig (306), etc.
 
 
 
INDEX TO VOLUME III.
 
 
 
Abdominal muscles, 675
 
Abdominal pore, 626, 749
 
Acipenser, development of, 102; affinities
of, 1 1 8 ; comparison of gastrula of, 279 ;
pericardial cavity of, 627
 
Actinotrocha, 373
 
Air-bladder of Teleostei, 77; Lepidosteus,
117; blood supply of, 645 ; general account of, 763 ; homologies of, 766
 
Alciope, eye of, 480
 
Alisphenoid region of skull, 569
 
Alimentary canal and appendages, development of, 754
 
Alimentary tract ofAscidia, 18; Molgula,
22; Pyrosoma, 24; Salpa, 31 ; Elasmobranchii, 52; Teleostei, 75; Petromyzon, 93, 97; Acipenser, no; Amphibia, 129, 136; Chick, 167; respiratory
region of, 754; temporary closure of
oesophageal region of, 759
 
Allantois, development of in Chick, 191,
198; blood-vessels of in Chick, 193;
Lacerta, 205, 209; early development of
in Rabbit, 229, of Guinea-pig, 264;
origin of, 309. See also ' Placenta ' and
'Bladder''
 
Alternation of generations in Ascidians,
origin of, 35 ; in Botryllus, 35 ; Pyrosoma, 36; Salpa, 36; Doliolum, 36
 
Alytes, branchial chamber of, 136; yolksack of, 139; branchiae, 141 ; Miillerian
duct of, 710
 
Amblystoma, ovum of, 120; larva of, 142,
 
H3
 
Amia, ribs of, 561
 
Ammocoetes, 95; metamorphosis of, 97;
 
eye of, 498
Amnion, early development of in Chick,
 
185; later history of in Chick, 196;
 
Lacerta, 204, 210; Rabbit, 229; origin
 
of, 3.07. 39
 
Amphibia, development of, 120; viviparous, 121; gastrula of, 277; suctorial
mouth of, 317; cerebellum of, 426; infundibulum of, 431; pineal gland of,
433; cerebrum of, 439; olfactory lobes
of, 444; nares of, 553; notochord and
its sheath, 548; vertebral column of,
554; ribs of, 561 ; branchial arches of,
574; mandibular and hyoid arches of,
582 ; columella of, 582 ; pectoral girdle
of, 605; pelvic girdle of, 607; limbs of,
619; heart of, 638; arterial system of,
f>45 ; venous system of, 655 ; excretory
 
 
 
system of, 707 ; vasa efierentia of, 711;
liver of, 769; postanal gut of, 774;
stomodaeum of, 778
 
Amphiblastula larva of Porifera, 344
 
Amphioxus, development of, i ; gastrula
of, 275 ; formation of mesoblast of, 292 ;
development of notochord of, 293; head
of, 314; spinal nerves of, 461; olfactory organ of, 462 ; venous system
of, 651; transverse abdominal muscle
f> 673; generative cells of, 748; liver
of, 769; postanal gut of, 772; stomodaeum of, 777
 
Amphistylic skulls, 578
 
Angular bone, 594
 
Anterior abdominal vein, 653
 
Anura, development of, 121; epiblast of,
125; mesoblast of, 128; notochord of,
128; hypoblast of, 129; general growth
of embryo of, 131; larva of, 134; vertebral column of, 556 ; mandibular arch
of, 584
 
Anus of Amphioxus, 7 ; Ascidia, 18; Pyrosoma, 28 ; Salpa, 31 ; Elasmobranchii,
57; Amphibia, 130, 132; Chick, 167;
primitive, 324
 
Appendicularia, development of, 34
 
Aqueductus vestibuli, 519
 
Aqueous humour, 497
 
Arachnida, nervous system of, 409; eye
of, 481
 
Area, embryonic, of Rabbit, 218; epiblast
 
of, 219; origin of embryo from, 228
 
area opaca of Chick, 150; epiblast,
 
hypoblast, and mesoblast of, 159
area pellucida of Chick, 150; of Lacerta, 202
 
area vasculosa of Chick, 194; mesoblast of, 1 60; of Lizard, 209; Rabbit,
228, 229
 
Arteria centralis retinas, 503
 
Arterial system of Petromyzon, 97; constitution of in embryo, 643 ; of Fishes,
644; of Amphibia, 645; of Amniota, 647
 
Arthropoda, head of, 313 ; nervous system
of, 409 ; eye of, 480 ; excretory organs
of, 688
 
Articular bone of Teleostei, 581 ; of Sauropsida, 588
 
Ascidia, development of, 9
 
Ascidians. See 'Tunicata'
 
Ascidiozooids, 25
 
Atrial cavity of Amphioxus, 7; Ascidia,
18; Pyrosoma, 24
 
 
 
7 82
 
 
 
INDEX.
 
 
 
Atrial pore of Amphioxus, 7; Ascidia, 20;
Pyrosoma, 28 ; Salpa, 32
 
Auditory capsules, ossifications in, 595,
59.6
 
Auditory involution of Elasmobranchii,
57; Teleostei, 73; Petromyzon, 89,
92; Acipenser, 106; Lepidosteus, 114;
Amphibia, 127; Chick, 170
 
Auditory nerve, development of, 459
 
Auditory organs, of Ascidia, 15; of Salpa,
31; of Ammocoetes, 98; Ganoidei, 108,
114; of Amphibia, 127; of Aves, 170;
general development of, 512; of aquatic
forms, 512; of land forms, 513; of
Ccelenterata, 513; of Mollusca, 515;
of Crustacea, 516; of Vertebrata, 517;
of Cyclostomata, 89, 92, 518; of Teleostei, Lepidosteus and Amphibia,
518; of Mammalia, 519; accessory
structures of, 527; ofTunicata, 528
 
Auriculo-ventricular valves, 642
 
Autostylic skulls, 579
 
Aves, development of, 145; cerebellum
of, 426; midbrain of, 427; infundibulum of, 431; pineal gland of, 434;
pituitary body of, 436; cerebrum of,
439 ; olfactory lobes of, 444 ; spinal
nerves of, 449 ; cranial nerves of, 455 ;
vagus of, 458; glossopharyngeal of,
458; vertebral column of, 557; ossification of vertebral column of, 558;
branchial arches of, 572, 573; pectoral
girdle of, 603; pelvic girdle of, 608;
heart of, 637 ; arterial system of, 647 ;
venous system of, 658; muscle-plates
of, 670; excretory organs of, 714; mesonephros of, 715; pronephros of, 718;
Miillerian duct of, 718, 720; nature of
pronephros of, 721 ; connection of Miillerian duct with Wolffian in, 720 ;
kidney of, 722; lungs of, 764; liver of,
769; postanal gut of, 774
 
Axolotl, 142, 143; ovum of, 120; midbrain of, 427; mandibular arch of, 583
 
Basilar membrane, 524
 
Basilar plate, 565
 
Basipterygium, 612
 
Basisphenoid region of skull, 569
 
Bilateral symmetry, origin of, 373-376
 
Bile duct, 770
 
Bladder, Amphibia, 131 ; of Amniota, 726
 
Blastodermic vesicle, of Rabbit, first development of, 217; of 7th day, 222;
Guinea-pig, 263; meaning of, 291
 
Blastoderm of Pyrosoma, 24; Elasmobranchii, 41; Chick, 150; Lacerta 202
 
Blastopore, of Amphioxus, 2; of Ascidia,
II ; Elasmobranchii, 42, 54, 62 ; Petromyzon, 87; Acipenser, 104 ; Amphibia,
125, 130; Chick, 153; Rabbit, 216;
true Mammalian, 226; comparative
history of closure of, 284, 288; summary of fate of, 340; relation of to
primitive anus, 324
 
 
 
Blood-vessels, development of, 633
 
Body cavity, of Ascidia, 2 1 ; Molgula, 2 1 ;
Salpa, 31; Elasmobranchii, 47 ; of Teleostei, 75 ; Petromyzon, 94 ; Chick,
169; development of in Chordata, 325;
views on origin of, 356 360, 377; of
Invertebrata, 623; of Chordata, 624;
of head, 676
 
Bombinator, branchial chamber of, 136;
vertebral column of, 556
 
Bonellia, excretory organs of, 687
 
Bones, origin of cartilage bones, 542 ;
origin of membrane bones, 543; development of, 543; homologies of membrane bones, 542 ; homologies of cartilage bones, 545
 
Brachiopoda, excretory organs of, 683 ;
generative ducts of, 749
 
Brain, of Ascidia, IT, 15; Elasmobranchii, 56, 59, 60; Teleostei, 77; Petromyzon, 89, 92 ; Acipenser, 105 ; Lepidosteus, 113; early development of in
Chick, 170; flexure of in Chick, 175;
later development of in Chick, 176;
Rabbit, 229, general account of development of, 419; flexureof, 420; histogeny of, 422
 
Branchial arches, prseoral, 570; disappearance of posterior, 573; dental plates
of in Teleostei, 574; relation of to
head cavities, 571 ; see ' Visceral arches'
 
Branchial chamber of Amphibia, 136
 
Branchial clefts, of Amphioxus, 7 ; of
Ascidia, 18, 20; Molgula, 23; Salpa,
32; of Elasmobranchii, 57, 59 01;
Teleostei, 77; Petromyzon, 91, 96;
Acipenser, 105; Lepidosteus, 114, 116;
Amphibia, 132, 133; Chick, 178;
Rabbit, 231; praeoral, 312, 318; of
Invertebrata, 326; origin of, 326
 
Branchial rays, 574
 
Branchial skeleton, development of, 572,
592; of Petromyzon, 96, 312, 571; of
Ichthyopsida, 572; dental plates of in
Teleostei, 574; relation of to head
cavities, 572
 
Branchiae, external of Elasmobranchii, 6r,
62; of Teleostei, 77; Acipenser, 107;
Amphibia, 127, 133, 135
 
Brood-pouch, of Salpa, 29 ; Teleostei, 68,
Amphibia, 12 1
 
Brown tubes of Gephyrea, 686
 
Bulbus arteriosus, of Pishes, 638 ; Amphibia, 639
 
Bursa Fabricii, 167, 779
 
Canalis auricularis, 639
Canalis reuniens, 521
Capitellidre, excretory organs of, 683
Carcharias, placenta of, 66
Cardinal vein, 652
Carnivora, placenta of, 250
Carpus, development of, 620
Cartilage bones of skull, 595 ; homologies
of, 595
 
 
 
INDEX.
 
 
 
783
 
 
 
Cat, placenta of, 250
 
Caudal swellings of Elasmobranchii, 46,
 
55; Teleostei, 72; Chick, 162, 170
Cephalic plate of Elasmobranchii, 55
Cephalochorda, development of, i
Cephalopoda, eyes of, 473 477
Cerebellum, Petromyzon, 93; Chick, 176;
 
general account of development of, 424,
 
425
 
Cerebrum of Petromyzon, 93, 97; Chick,
175 ; general development of, 429, 438;
transverse fissure of, 443
Cestoda, excretory organs of, 68 1
Cetacea, placenta, 255
Chtetognatha, nervous system of, 349;
eye of, 479 ; generative organs of, 743 ;
generative ducts of, 749
Chcetopoda, head of, 313; eyes of, 479;
excretory organs of, 683; generative
organs of, 743 ; generative ducts of, 749
Charybdnea, eye of, 472
Cheiroptera, placenta of, 244
Cheiropterygium, 618; relation of to ich
thyopterygium, 621
 
Chelonia, development of, 210; pectoral
girdle of, 603 ; arterial system of, 649
Chick, development of, 145 ; general
growth of embryo of, 1 70 ; rotation of
embryo of, 173; fcetal membranes of,
185; epiblast of, 150, 166; optic nerve
and choroid fissure of, 500
 
Chilognatha, eye of, 481
 
Chilopoda, eye of, 481
 
Chimasra, lateral line of, 539 ; vertebral
column of, 548; nares of, 533
 
Chiromantis, oviposition of, 121
 
Chorda tympani, development of, 460
 
Chordata, ancestor of, 311; branchial
system of, 312; evidence from Ammocuetes, 312; head of, 312; mouth of,
318; table of phylogeny of, 327
 
Chorion, 237; villi of, 237, 257
 
Choroid coat, Ammoccetes, 99; general
account of, 487
 
Choroid fissure, of Vertebrate eye, 486,
493 ; of Ammocoetes, 498 ; comparative
development of, 500; of Chick, 501;
of Lizards, 501 ; of Elasmobranchii,
502 ; of Teleostei, 503 ; Amphibia, 503 ;
Mammals, 503, 504
 
Choroid gland, 320
 
Choroid pigment, 489
 
Choroid plexus, of fourth ventricle, 425 ;
of third ventricle, 432 ; of lateral ventricle, 442
 
Ciliated sack of Ascidia, 18; Pyrosoma,
26; Salpa, 31
 
Ciliary ganglion, 461
 
Ciliary muscle, 490
 
Ciliary processes, 488; comparative development of, 506
 
Clavicle, 600
 
Clitoris, development of, 727
 
Clinoid ridge, 569
 
Cloaca, 766
 
 
 
Coccygeo-mesenteric vein, 66 1
 
Cochlear canal, 519
 
Coecilia, development of, 143; pronephros
of, 707; mesonephros of, 709; Mill
lerian duct of, 710
 
Coelenterata, larvae of, 367 ; eyes of, 47 1 ;
auditory organs of, 513; generative
organs of, 741
 
Columella auris, 529; of Amphibia, 582 ;
of Sauropsida, 588
 
Commissures, of spinal cord, 417; of
brain, 431, 432, 439, 443
 
Coni vasculosi, 724
 
Conus arteriosus, of Fishes, 638; of Amphibia, 638
 
Coracoid bone, 599
 
Cornea, of Ammocretes, 99 ; general development of, 495 ; corpuscles of, 496 ;
comparative development of, 499; of
Mammals, 499
 
Coronoid bone, 595
 
Corpora geniculata interna, 428
 
Corpora quadrigemina, 428
 
Corpora striata, development of, 437
 
Corpus callosum, development of, 443
 
Corti, organ of, 522; structure of, 525;
fibres of, 525 ; development of, 526
 
Cranial flexure, of Elasmobranchii, 58,
60; of Teleostei, 77; Petromyzon, 93,
94; of Amphibia, 131, 132; Chick,
174; Rabbit, 231; characters of, 321;
significance of, 322
 
Cranial nerves, development of, 455;
relation of to head cavities, 461 ; anterior roots of, 462 464; view on
position of roots of, 466
 
Crocodilia, arterial system of, 649
 
Crura cerebri, 429
 
Crustacea, nervous system of, 41 1 ; eye of,
481; auditory organs of, 515; generative cells of, 745 ; generative ducts of,
 
75
 
Cupola, 524
 
Cutaneous muscles, 676
 
Cyathozooid, 25
 
Cyclostomata, auditory organs of, 517;
olfactory organ of, 532; notochord and
vertebral column of, 546, 549; abdominal pores of, 626 ; segmental duct of,
700 ; pronephros of, 700 ; mesonephros
of, 700 ; generative ducts of, 733, 749 ;
venous system of, 651 ; excretory organs
of, 700
 
Cystignathus, oviposition of, 122
 
Dactylethra, branchial chamber of, 136;
 
branchise of, 136; tadpole of, 140
Decidua reflexa, of Rat, 242 ; of Insecti
vora, 243; of Man, 245
Deiter's cells, 526
Dental papilla, 777
Dental capsule, 777
Dentary bone, 595
Dentine, 780
Descemet's membrane, 496
 
 
 
784
 
 
 
INDEX.
 
 
 
Diaphragm, 631 ; muscle of, 676
 
Dipnoi, nares of, 534; vertebral column
of, 548; membrane bones of skull of,
592 ; heart of, 638 ; arterial system of,
645 ; excretory system of, 707 ; stomodseum of, 777
 
Diptera, eye of, 481
 
Discophora, excretory organs of, 687
 
Dog, placenta of, 248
 
Dohni, on relations of Cyclostomata, 84 ;
on ancestor of Chordata, 311, 319
 
Doliolum, development of, 28
 
Ductus arteriosus, 649
 
Ductus Botalli, 648
 
Ductus Cuvieri, 654
 
Ductus venosus Arantii, 663
 
Dugong, heart of, 642
 
Dysticus, eye of, 481
 
Ear, see ' Auditory organ '
 
Echinodermata, secondary symmetry of
larva of, 380; excretory organs of, 689 ;
generative ducts of, 752
 
Echinorhinus, lateral line of, 539; vertebral column of, 548
 
Echiurus, excretory organs of, 686
 
Ectostosis, 543
 
Edentata, placenta of, 248, 250, 256
 
Eel, generative ducts of, 703
 
Egg-shell of Elasmobranchii, 40 ; Chick,
146
 
Elasmobranchii, development of, 40; viviparous, 40; general features of development of, 55 ; gastrulaof, 281 ; development of mesoblast of, 294 ; notochord of, 294 ; meaning of formation of
mesoblast of, 295; restiform tracts of,
425 ; optic lobes of, 427 ; cerebellum of,
425 ; pineal gland of, 432 ; pituitary
body of, 435 ; cerebrum of, 438 ; olfactory lobes of, 444 ; spinal nerves, 449 ;
cranial nerves of, 457; sympathetic
nervous system of, 466; nares of, 533;
lateral line of, 539; vertebral column of,
549 ; ribs of, 560 ; parachordals of, 567 ;
mandibular and hyoid arches of, 576 ;
pectoral girdle of, 600 ; pelvic girdle of,
607; limbs of, 609; pericardial cavity
of, 627; arterial system of, 644 ; venous
system of, 65 1 ; muscle-plates of, 668 ;
excretory organs of, 690 ; constitution
of excretory organs in adult of, 697;
spermatozoa of, 747 ; swimming-bladder of, 763 ; intestines of, 767 ; liver of,
769; postanal gut of, 772
 
Elrcoblast of Pyrosoma, 28; Salpa, 30
 
Elephant, placenta of, 249
 
Embolic formation of gastrula, 333
 
Enamel organ, 777
 
Endolymph of ear, 522
 
Endostosis, 543
 
Endostyle of Ascidia, 18, 759; Pyrosoma,
25; Salpa, 32
 
Epiblast, of Elasmobranchii, 47 ; Teleostei, 71, 75; Petromyzon, 86; Lcpid
 
 
osteus, 112; Amphibia, 122, 125;
Chick, 149, 166; Lacerta, 203; Rabbit,
216, 219; origin of in Rabbit, 221 ;
comparative account of development
of, 300
 
Epibolic formation of gastrula, 334
 
Epichordal formation of vertebral column,
556
 
Epicrium glutinosum, 143
 
Epidermis, in Ccelenterata, 393; protective structures of, 394
 
Epididymis, 724
 
Epigastric vein, 653
 
Episkeletal muscles, 676
 
Episternum, 602
 
Epoophoron, 725
 
Ethmoid bone, 597
 
Ethmoid region of skull, 570
 
Ethmopalatine ligament of Elasmobranchs, 576
 
Euphausia, eye of, 483
 
Eustachian tube, of Amphibia, 135;
Chick, 1 80; Rabbit, 232; general
development of, 528
 
Excretory organs, general constitution of,
680; of Platyelminthes, 680; of Mollusca, 681; of Polyzoa, 682; of Brachiopoda, 683 ; of Choetopoda, 683 ; of
Gephyrea, 686 ; of Discophora, 687 ; of
Arthropoda, 688; of Nematoda, 689;
of Echinodermata, 689 ; constitution of
in Craniata, 689; of Elasmobranchii,
690; constitution of in adult Elasmobranch, 697; of Petromyzon, 700; of
Myxine, 701 ; of Teleostei, 701 ; of
Ganoidei, 704; of Dipnoi, 707; of
Amphibia, 707; of Amniota, 713;
comparison of Vertebrate and Invertebrate, 737
 
Excretory system, of Elasmobranchii, 49 ;
Teleostei, 78; Petromyzon, 95, 98;
Acipenser, 99; Amphibia, 133
 
Exoccipital bone, 595
 
Exoskeleton, dermal, 393 395 ; epidermal, 393396
 
External generative organs, 726
 
Extra-branchial skeleton, 572
 
Eye, of Ascidia, 16; Salpa, 31; Elasmobranchii, 56, 57, 58; Teleostei, 73;
Petromyzon, 92, 98; Aves, i/o; Rabbit, 229; general development of, 470;
evolution of, 470, 471; simple, 480;
compound, 481 ; aconous, 482; pseudoconous, 482 ; of Invertebrata, 471; of
Vertebrata, 483 ; comparative development of Vertebrate, 497 ; of Ammoccetes, 497 ; of Tunicata, 507 ; of Chordata, general views on, 508 ; accessory
eyes of Fishes, 509; muscles of, 677
 
Eyelids, development of, 506
 
Falciform ligament, 757
 
Falx cerebri, 439
 
Fasciculi terctes, of Elasmobranchii. 426
 
Feathers, development of, 396
 
 
 
INDEX.
 
 
 
785
 
 
 
Fenestra rotunda and ovalis, 529
 
Fertilization, of Amphioxus, 2 ; of Urochorda, 9; Salpa, 29; Elasmobranchii,
46; of Teleostei, 68; Petromyzon, 84 ;
Amphibia, 120; Chick, 145 ; Reptilia,
202 ; meaning of, 331
 
Fifth nerve, development of, 460
 
Fifth ventricle, 443
 
Fins, of Elasmobranchii, 62 ; Teleostei,
78; Petromyzon, 94, 95; Acipenser,
109; Lepidosteus, 118; relation of
paired to unpaired, 611, 612 ; development of pelvic, 614; development of
pectoral, 615; views on nature of paired
fins, 616
 
Fissures of spinal cord, 417
 
Foetal development, 360 ; secondary variations in, 361
 
Foot, 618
 
Foramen of Munro, 430, 438
 
Foramen ovale, 642
 
Forebrain, of Elasmobranchii, 55, 59, 60;
Petromyzon, 93 ; general development
of, 428
 
Formative cells, of Chick, 154
 
Fornix, development of, 443
 
Fornix of Gottsche, 428
 
Fourth nerve, 464
 
Frontals, 592
 
Fronto-nasal process of Chick, 179
 
Gaertner's canals, 724
 
Gall-bladder, 770
 
Ganoidei, development of, 102; relations
of, 118; nares of, 534; notochord of,
546 ; vertebral column of, 546, 553 ;
ribs of, 561 ; pelvic girdle of, 606; arterial system of, 645 ; excretory organs
of, 704; generative ducts of, 734
 
Gastropoda, eye of, 472
 
Gastrula, of Amphioxus, 2; of Ascidia, lo;
Elasmobranchii, 43, 44 ; Petromyzon,
86; Acipenser, 103; Amphibia, 123;
comparative development of, in Invertebrata, 275 ; comparison of Mammalian, 291 ; phylogenetic meaning of, 333 ;
ontogeny of (general), 333 ; phylogeny
of, 338 343 ; secondary types of, 34!
 
Geckos, vertebral column of, 557
 
Generative cells, development of, 74! ;
origin of in Ccelenterata, 741 ; of Invertebrata, 743 ; of Vertebrata, 746
 
Generative ducts, of Teleostei, 704, 735 ;
of Ganoids, 704; of Cyclostomata, 733;
origin of, 733 ; of Lepidosteus, 735,
750 ; development and evolution of,
748 ; of Ccelenterata, 748 ; of Sagitta,
749 ; of Tunicata, 749 ; Cheetopoda,
Gephyrea, etc., 749; of Mollusca, 751;
of Discophora, 751 ; of Echinodermata,
 
75*
 
Generative system of Elasmobranchii, 51
Gephyrea, nervous system of, 412; excretory organs of, 686 ; generative cells of,
743 ; generative ducts of, 749
 
B. III.
 
 
 
Germinal disc, of Elasmobranchii, 40;
Teleostei, 68 ; Chick, 147
 
Germinal epithelium, 746
 
Germinal layers, summary of organs <lrrived from, in Vertebrata, 304 ; historical account of views of, 332 ; homologies of in the Metazoa, 345
 
Germinal wall of Chick, 152, 159; structure and changes of, 160
 
Geryonia, auditory organ of, 5 r 5
 
Gill of Salpa, 31
 
Giraldes, organ of, 725
 
Glands, epidermic, development of, 397
 
Glomerulus, external, of Chick, 716
 
Glossopharyngeal nerve, development of,
 
45 6 > 457
Grey matter of spinal cord, 417; of brain,
 
423
Growth in length of Vertebrate embryo,
 
306
Guinea-pig, primitive streak of, 223;
 
notochord of, 226 ; placenta of, 242 ;
 
development of, 262
Gymnophiona, see ' Ccecilia '
 
Habenula perforata, 525
 
Hairs, development of, 396
 
Halichrerus, placenta of, 250
 
Hand, 619
 
Head, comparative account of, 313; segmentation of, 314
 
Head cavities, of Elasmobranchii, 50 ;
Petromyzon, 90, 96; Amphibia, 127;
general development of, 676
 
Head-fold of Chick, 157, 167
 
Head kidney, see ' Pronephros '
 
Heart, of Pyrosoma, 25; Elasmobranchii,
50, 58 ; Petromyzon, 94, 97 ; Acipenser, 106; Chick, 170 ; first appearance
of in Rabbit, 230; general development
of, 633 ; of Fishes, 635, 637 ; of Mammalia, 638; of Birds, 637, 639; meaning of development of, 637 ; of Amphibia, 638 ; of Amniota, 639 ; change of
position of, 643
 
Hind-brain, Elasmobranchii, 55, 59, 60 ;
Petromyzon, 93 ; general account of,
424
 
Hippocampus major, development of, 442
 
Hirudo, development of blood-vessels of,
633 ; excretory organs of, 688
 
Horse, placenta of, 253
 
Hyaloid membrane, 492
 
Hylodes, oviposition of, 1 21 ; metamorphosis of, -1 37
 
Hyobranchial cleft, 572
 
Hyoid arch, of Chick, 179; general account of, 572, 575 ; modifications of,
e !73> 577 > f Elasmobranchii, 576; of
Teleostei, 577 ; of Amphibia, 582 ;
of Sauropsida, 588; of Mammalia,
 
589
 
Hyomandibular bar of Elasmobranchii,
576, 577 ; of Teleostei, 579 ; of Amphibia, 582
 
50
 
 
 
;86
 
 
 
INDEX.
 
 
 
Hyomandibular cleft, of Fetromyzon, 91 ;
Chick, 179 ; general account of, 572
 
Hyostylic skulls, 582
 
Hypoblast of Elasmobranchii, 5! ; Teleostei, 71, 75; Petromyzon, 86; Acipenser, 104; Lepidosteus, 113; Amphibia,
122, 129; Chick, 151, 167 ; Lacerta,
203; Rabbit, 215, 216, 219 ; origin of
in Rabbit, 220
 
Hyposkeletal muscles, 675
 
Ilyrax, placenta of, 249
 
Incus, 529, 590
 
Infraclavicle, 600
 
Infundibulum of Petromyzon, 92 ; Chick,
175 ; general development of, 430
 
Insectivora, placenta of, 243
 
Insects, nervous system of, 410 ; eye of,
481; generative organs of, 745; generative ducts of, 751
 
Intercalated pieces of vertebral column,
 
55 1
 
Interclavicle, homologies of, 602
 
Intermediate cell-mass of Chick, 183
 
Intermuscular septa, 672
 
Interorbital septum, 570
 
Interrenal bodies, 665
 
Iris, 489 ; comparative development of,
 
506
 
Iris of Ammoccetes, 98
Island of Reil, 444
 
Jacobson's organ, 537
Jugal bone, 594
 
Kidney, see ' Metanephros '
 
Labia majora, development of, 727
 
Labial cartilages, 597
 
Labium tympanicum, 525 ; vestibulare,
 
5 2 5
 
Lacertilia, general development of, 202 ;
nares of, 537 ; pectoral girdle of, 603 ;
pelvic girdle of, 607 ; arterial system
of, 649
 
Lacrymal bone, 593
 
Lacrymal duct, 506
 
Lacrymal glands, 506
 
Lremargus, vertebral column of, 548
 
Lagena, 524
 
Lamina spiralis, 524
 
Lamina terminalis, 438
 
Larva of Amphioxus, 2 ; of Ascidia, 1 5
it ; Teleostei, 81 ; Petromyzon, 89, 95;
Lepidosteus, 117, 318; Amphibia, 134,
142; types of, in the Invertebrata, 363
 
Larvre, nature, origin, and affinities of,
360 386; secondary variations of less
likely to be retained, 362 ; ancestral
history more fully recorded in, 362 ;
secondary variations in development of,
363 ; ontogenetic record of secondary
variations in, 361; of freshwater and
land animals, 362; types of, 36.2; phosphorescence of, 364; of Coelenterata,
 
 
 
367 ; table of, 365 ; of Invertebrata,
367 et seq.
 
Larynx, 766
 
Lateral line sense organs, 538 ; comparison of, with invertebrate, 538 ; development of, in Teleostei, 538 ; development of, in Elasmobranchii, 539
 
Lateral ventricle, 438 ; anterior cornu of,
440 ; descending cornu of, 440 ; choroicl
plexus of, 443
 
Layers, formation of, in Elasmobrancliii,
41, 56 ; Teleostei, 71 ; Petromyzon,
85 ; Acipenser, 103 ; Lepidosteus, 1 1 1 ;
Amphibia, 121; Chick, 150, 152;
Lacerta, 202; Rabbit, 215 227; comparison of Mammalia with lower forms,
226, 289; comparison of formation of
in Vertebrata, 275; origin and homologies of, in the Metazoa, 331
 
Leech, see ' Hirudo '
 
Lemuridre, placenta, 256
 
Lens, of Elasmobranchii, 57, 58 ; Petromyzon, 94, 99; Acipenser, 106 ;
Lepidosteus, 115 ; Amphibia, 127 ;
Chick, 177 ; of Vertebrate eyes, 485 ;
general account of, 493 ; capsule of, 493 ;
comparative development of, 499 ; of
Amphibia, Teleostei, Lepidosteus, 499
 
Lepidosteus, development of, 1 1 1 ; larva
of, 117; relations of, 119; spinal nerves
of, 455; ribs of, 561 ; generative ducts
of, 704, 735 ; swimming-bladder of,
 
763
 
Ligamentum pectinatum, 490
 
Ligamentum suspensorium, 557, 558
 
Ligamentum vesicse medium, 239
 
Limbs, of Elasmobranchii, 59 ; Teleostei,
80 ; first appearance of in Chick,
184 ; Rabbit, 232 ; muscles of, 673 ; of
Fishes, 609; relation of, to unpaired fins
of Fishes, 611, 612; of Amphibia, 61 8
 
Liver of Teleostei, 78 ; Petromyzon, 95,
96; Acipenser, no; Amphibia 130;
general account of, 769
 
Lizard, development of, 202; general
growth of embryo of, 208 ; Mullerian
duct of, 721
 
Lizzia, eye of, 471
 
Lobi inferiores, 431
 
Lungs of Amphibia, 137 ; development
of, 763 ; homology of, 766
 
Lymphatic system, 664
 
Malleus, 529, 591 ; views on, 591
Malpighian bodies, development of accessory in Elasmobranchs, 695
Mammalia, development of, 214; comparison of gastrula of, 291 ; cerebellum
of, 427 ; infundibulum of, 431 ; pineal
gland of, 434; pituitary body of, 436;
cerebrum of, 439 ; spinal nerves of, 449 ;
sympathetic of, 466; vertebral column
of, 558; branchial arches of, 573, 574;
mandibular and hyoid arches of, 589 ;
pectoral girdle of, 604; pelvic girdle of,
 
 
 
INDEX.
 
 
 
787
 
 
 
608 ; heart of, 636 ; arterial system of,
647; venous system of, 661 ; muscleplates of, 671 ; mesonephros of, 714;
testicular network of, 724 ; urinogenital
sinus of, 727 ; spermatozoa of, 747 ;
lungs of, 765 ; intestines of, 768 ; liver
of> 769; postanal gut of, 774; stomodseum of, 775
 
Mammary gland, development of, 398
Man, placenta of, 244 ; general account of
development of, 265 ; characters of embryo of, 270
 
Mandibular arch of Elasmobranchii, 62,
576; Petromyzon, 91 ; Acipenser, 106,
116; Chick, 179; general account of,
 
572, 575; modification of to form jaws,
 
573, 575; of Teleostei, 580; of Amphibia, 582; Sauropsida, 588; Mammalia, 589
 
Mandibular bar, evolution of, 311, 321
 
Manis, placenta of, 256
 
Marsupial bones, 608
 
Marsupialia, foetal membranes of, 240 ; cerebellum of, 426 ; corpus callosum of,
' 443 ; uterus of, 726
 
Maxilla, 594
 
Meatus auditorius externus, of Chick, 181;
development of, 527
 
Meckelian cartilage, of Elasmobranchii,
576; of Teleostei, 581 ; of Amphibia,
584, 585; of Sauropsida, 588 ; of Mammalia, 590
 
Mediastinum anterior and posterior, 630
 
Medulla oblongata, of Chick, 176 ; general development of, 425
 
Medullary plate of Amphioxus, 4, 5 ; of
Ascidia, n; Elasmobranchii, 44, 47,
55; Teleostei, 72; Petromyzon, 88;
Acipenser, 104; Lepidosteus, 1 1 1 ; Amphibia, 126, 127, 131; Chick, 159;
Lacerta, 204; Rabbit, 223, 227, 228;
primitive bilobed character of, 303, 317
 
Medusae, auditory organs of, 513
 
Membrana capsulo-pupillaris, 494, 504,
 
507
 
Membrana elastica externa, 546
 
Membrana limitans of retina, 491
 
Membrana tectoria, 522, 525
 
Membrane bones, of Amphibia, 582 ; of
Sauropsida, 588; of Mammalia, 590;
of mandibular arch, 593 ; of pectoral
girdle, 599, 602 ; origin of, 592 ; homologies of, 593
 
Membranous labyrinth, development of
in Man, 519
 
Menobranchus, branchial arches of, 142
 
Mesenteron of Elasmobranchii, 43 ; Teleostei, 75 ; Petromyzon, 85 ; Acipenser,
104; Amphibia, 123, 124, 129; Chick,
167; general account of, 754
 
Mesentery, 626, 756
 
Mesoblast, of Amphioxus, 6 ; Ascidia,
17, 20; Pyrosoma, 24; Salpa, 30;
Elasmobranchii, 44, 47; Teleostei, 75;
Petromyzon, 86; Acipenser, 105; Lepi
 
 
dosteus, 113; Amphibia, 125, 128, 129;
of Chick, 154, 167; double origin of in
Chick, 154, 158, 159; origin of from
lips of blastopore in Chick, 158; of
area vasculosa of Chick, iOo; Lacerta,
203; origin of in Rabbit, 218, 223; of
area vasculosa in Rabbit, 227; comparative account of formation of, 292 ;
discussion of development of in Vertebrata, 297 ; meaning of development
of in Amniota, 298; phylogenetic origin
of, 346 ; summary of ontogeny of, 349
352 ; views on ontogeny of, 352 360
 
Mesoblastic somites, of Amphioxus, 6 ;
Elasmobranchii, 48, 55 ; Petromyzon,
88 ; Acipenser, 105 ; Lepidosteus,
114; Amphibia, 129, 131; Chick,
161, 1 80; Rabbit, 228; development
of in Chordata, 325; meaning of development of, 331; of head, 676
 
Mesogastrium, 758
 
Mesonephros, of Teleostei, 78, 702; Petromyzon, 95, 98, 700; Acipenser, 1 10,
705; Amphibia, 134, 708; Chick, 184,
714; general account of, 690 ; development of in Elasmobranchs, 691 ; of
Cyclostomata, 700 ; Ganoidei, 705 ;
sexual and non-sexual part of in Amphibia, 710; of Amniota, 713, 724;
summary and general conclusions as
to, 729; relation of to pronephros, 731
 
Mesopterygium, 616
 
Metagenesis of Ascidians, 34
 
Metamorphosis of Amphibia, 137, 140
 
Metanephros, 690; development of in
Elasmobranchii, 697; of Amphibia,
712; of Amniota, 713; of Chick, 722;
of Lacertilia, 723; phylogeny of, 736
 
Metapterygium, 616
 
Metapterygoid, of Elasmobranchii, 576;
of Teleostei, 581
 
Metazoa, evolution of, 339, 342 ; ancestral
form of, 333, 345
 
Mid-brain, of Elasmobranchii, 55, 58,
59; Petromyzon, 92; general account
of development of, 427
 
Moina, generative organs of, 745
 
Molgula, development of, 22
 
Mollusca, nervous system of, 414 ; eyes of,
472; auditory organs of, 515; excretory organs of, 68 1
 
Monotremata, foetal membranes of, 240 ;
cerebellum of, 426; corpus callosum
of, 443 ; cerebrum of, 443 ; urinogenital sinus of, 726
 
Mormyrus, generative ducts of, 704
 
Mouth, of Amphioxus, 7; of Ascidia, 18;
Pyrosoma, 27; Salpa, 31; Elasmobranchii, 57, 60, 61, 62; Petromyzon,
92, 94, 95, 99; Acipenser, 107; Lepidosteus, 118; Amphibia, 129, 132,
"134; Rabbit, 231 ; origin of, 317
 
Mouth, suctorial, of Petromyzon, 99;
Acipenser, 107; Lepidosteus, 116, 317;
Amphibia, 133, 141, 317
 
 
 
;88
 
 
 
INDEX.
 
 
 
Mullerian duct, 690; of Elasmobranchs,
693 ; of Ganoids, 704 ; of Amphibia,
710; of Aves, 717,720; opening of into cloaca, 727; origin of, 733; summary of development of, 733; relation
of to pronephros, 733
 
Muscle-plates, of Amphioxus, 6; Elasmobranchii, 49, 668 ; Teleostei, 670 ;
Petromyzon, 94; Chick, 183, 670; general development of, 669 ; of Amphibia,
670; Aves, 670; of Mammalia, 671;
origin of muscles from, 672
 
Muscles, of Ascidia, II, 17; development
of from muscle-plates, 672; of limbs,
673 ; of head, 676 ; of branchial arches,
678; of eye, 678
 
Muscular fibres, epithelial origin of, 667
 
Muscular system, development of, 667;
of Chordata, 668
 
Mustelus, placenta of, 66
 
Myoepithelial cells, 667
 
Mysis, auditory organ of, 517
 
Myxine, ovum of, loo; olfactory organ
of, 533 ; portal sinus of, 652 ; excretory
system of, 701
 
Nails, development of, 397
 
Nares, of Acipenser, 108; of Ichthyopsida, 534; development of in Chick,
535; development of in Lacertilia, 537;
development of in Amphibia, 537
 
Nasal bones, 592
 
Nasal pits, Acipenser, 108; Chick, 176;
general development of, 531
 
Nematoda, excretory organs of, 689 ;
generative organs of, 745 ; generative
ducts of, 752
 
Nemertines, nervous system of, 311 ; excretory organs of, 68 1
 
Nerve cord, origin of ventral, 378
 
Nerves, spinal, 449 ; cranial, 455 466
 
Nervous system, central, general account
of development of in Vertebrata, 415 ;
conclusions as to, 445; sympathetic,
466
 
Nervous system, of Amphioxus, 4; Ascidia, 15, 16; Molgula, 22; Pyrosoma,
24, 25; Salpa, 30, 31; Elasmobranchii,
44; Teleostei, 77 ; Petromyzon, 89, 93;
Acipenser, 105; Amphibia, 126; comparative account of formation of central,
301; of Sagitta, 349; origin of in
Ccelenterata, 349; of pneoral lobe,
377, 380; evolution of, 400405; development of in Invertebrates, 406;
of Arthropoda, 408; of Gephyrea, 412;
Mollusca, 414
 
Neural canal, of Ascidia, 10; Teleostei,
72; Petromyzon, 88; Acipenser, 105;
Lepidosteus, 114; Amphibia, 126, 131 ;
Chick, 1 66, 171 ; Lacerta, 208; closure
of in Frog and Amphioxus, 279; closure
of in Elasmobranchii, 284; phylogcuctic origin of, 316
 
Neural crest, 449, 456, 457
 
 
 
Neurenteric canal, of Amphioxus, 4, 5 ;
Ascidia, lo; Elasmobranchii, 54; Petromyzon, 88 ; Acipenser, 105 ; Lepidosteus, 113; Aves, 162; Lacerta, 203,
206; general account of, 323; meaning
of, 3 2 3
 
Newt, ovum of, 120; development of,
I2 55 general growth of, 141
 
Notidanus, vertebral column of, 548;
branchial arches of, 572
 
Notochord of Amphioxus, 6; Ascidia,
II, 17; Elasmobranchii, 51; Teleostei,
74; Petromyzon, 86, 94; Acipenser,
104; Lepidosteus, 113; Amphibia, 128,
129; Chick, 157; canal of, in Chick,
163; Lacerta, 204, 205; Guinea-pig,
226; comparative account of formation
of, 292, 325; sheath of, 545; later
histological changes in, 546; cartilaginous sheath of, 547; in head, 566;
absence of in region of trabeculas, 567
 
Notodelphys, brood-pouch of, 121 ; branchiae of, 140
 
Nototrema, brood-pouch of, 121
 
Nucleus pulposus, 559
 
Oceania, eye of, 471
 
Occipital bone, 595
 
CEsophagus, solid, of Elasmobranchii,
61, 759; of Teleostei, 78
 
Olfactory capsules, 571
 
Olfactory lobes, development of, 444
 
Olfactory nerves, Ammoccetes, 99; general development of, 464
 
Olfactory organ, of aquatic forms, 531;
Insects and Crustacea, 531; of Tunicata, 532 ; of Amphioxus, 532 ; of
Vertebrata, 533; Petromyzon, 533;
of Myxine, 533
 
Olfactory sacks, of Elasmobranchii, 60;
Teleostei, 73; Petromyzon, 92, 97;
Acipenser, 106, 108; Lepidosteus, 116;
Chick, 176
 
Oligochreta, excretory organs of, 683
 
Olivary bodies, 426
 
Omentum, lesser and greater, 757
 
Onchidium, eye of, 473
 
Opercular bones, 593
 
Operculum, of Teleostei, 77; Acipenser,
107; Lepidosteus, 117, 118; Amphibia,
 
r 3.5.
 
Ophidia, development of, 210; arterial
system of, 649 ; venous system of, 656
 
Optic chiasma, 430, 493
 
Optic cup, retinal part of, 488 ; ciliary
portion of, 489
 
Optic lobes, 428
 
Optic nerve, development of, 492 ; comparative development of, 500
 
Optic thalami, development of, 431
 
Optic vesicle, of Elasmobranchii, 57 59;
Teleostei, 74, 499 ; Petromyzon, 89, 92 ;
Acipenser, 106; Lepidosteus, 115;
Chick, 170; Rabbit, 229; general development of, 429 ; formation of secon
 
 
INDKX.
 
 
 
7*9
 
 
 
dary, 487 ; obliteration of cavity of, 488 ;
comparative development of, 499; of
Lepidosteus and Teleostei, 499. See
also ' Eye '
 
Ora serrata, 488
 
Orbitosphenoid region of skull, 570
 
Organs, classification of, 391 ; derivation
of from germinal layers, 392
 
Orycteropus, placenta of, 249
 
Otic process of Axolotl, 583; of Frog,
585 et seq.
 
Otoliths, 512
 
Oviposition, of Amphioxus, i ; Elasmobranchii, 40; Teleostei, 68; Petromyzon, 84; Amphibia, 121; Reptilia, 202
 
Ovum, of Amphioxus, i; Pyrosoma, 23;
Elasmobranchii, 40; Teleostei, 68;
Petromyzon, 83 ; Myxine, loo; Acipenser, 102; Lepidosteus, in; Amphibia,
120; Chick, 146; Reptilia, 202 ; Mammalia, 214; of Porifera, 741; migration of in Ccelenterata, 742; Vertebrata, 746
 
Palatine bone, of Teleostei, 580; origin
of, 594
 
Pancreas, Acipenser, no; general development of, 770
 
Pancreatic caeca, of Teleostei, etc. 768
 
Papillae, oral, of Acipenser, 108; Lepidosteus, n6
 
Parachordals, 565, 566
 
Parasphenoid bone, 594
 
Parepididymis, 725
 
Parietal bones, 592
 
Paroophorori, 725
 
Parovarium, 725
 
Pectoral girdle, 599 ; of Elasmobranchs,
600; of Teleostei, 600; of Amphibia
and Amniota, 60 1 ; comparison of with
pelvic, 608
 
Pecten, eye of, 479
 
Pecten, of Ammoccetes, 498; of Chick,
501 ; Lizard, 501 ; Elasmobranchs, 501
 
Pedicle, of Axolotl, 484 ; of Frog, 485
 
Pelobates, branchial apertures of, 136;
vertebral column of, 556
 
Pelodytes, branchial chamber of, 135
 
Pelvic girdle, 606; of Fishes, 606; Amphibia and Amniota, 607 ; of Lacertilia, 607 ; of Mammalia, 608 ; comparison with pectoral, 608
 
Penis, development of, 727
 
Peribranchial cavity, of Amphioxus, 7;
of Ascidia, 18; Pyrosoma, 24
 
Pericardial cavity, of Pyrosoma, 26 ; Elasmobranchii, 49 ; Petromyzon, 94; general account of, 626; of Fishes, 627 ; of
Amphibia, Sauropsida and Mammalia,
628
 
Perichordal formation of vertebral column,
5^6
 
Perilymph of ear, 523
Periotic capsules, ossifications in, 595,
596
 
 
 
Peripatus, nervous system of, 409 ; eye of
480 ; excretory organs of, 688
 
Peritoneal membrane, 626
 
Petromyzon, development of, 83; affinities of, 83, 84; general development
of, 87; hatching of, 89; comparison of
gastrula of, 280; branchial skeleton of,
312, 572; cerebellum of, 425; pineal
gland of, 434 ; pituitary body of, 436 ;
cerebrum of, 439; auditory organ of,
517; olfactory organ of, 533; comparison of oral skeleton of with Tadpole,
586; pericardial cavity of, 627; abdominal pores of, 626 ; venous system of,
651 ; excretory organs of, 700; segmental duct of, 700; pronephros of, 700;
mesonephros of, 700 ; thyroid body of,
760; postanalgut of, 774; stomodx-um
 
of, 775
 
Phosphorescence of larvae, 364
 
Phylogeny, of the Chordata, 327; of the
Metazoa, 384
 
Pig, placenta of, 251; mandibular and
hyoid arches of, 589
 
Pineal gland, of Petromyzon, 93 ; Chick,
175; general development of, 432;
nature of, 432, 434
 
Pipa, brood-pouch of, 121 ; metamorphosis of, 139; yolk-sack of, 140; vertebral
column of, 556
 
Pituitary body, of Rabbit, 231 ; general
development of, 435 ; meaning of, 436 ;
Placenta, of Salpa, 29; Elasmobranchii, 66; of Mammalia, 232; villi of,
235 ; deciduate and non-deciduate, 239;
comparative account of, 239 259 ; characters of primitive type of, 240; zonary, 248; non-deciduate, 250; histology of, 257; evolution of, 259
 
Placoid scales, 395
 
Planorbis, excretory organs of, 68 1
 
Planula, structure of, 367
 
Pleural cavities, 631
 
Pleuronectidae, development of, 80
 
Pneumatoccela, characters of, 327
 
Polygordius, excretory organs of, 684
 
Polyophthalmus, eye of, 479
 
Polypedates, brood-pouch of, 121
 
Polyzoa, excretory organs of, 682 ; generative cells of, 745 ; generative ducts
 
of, 751
 
Pons Varolii, 426, 427
 
Pori abdominales, Ammoccetes, 99
 
Porifera, ancestral form of, 345 ; development of generative cells of, 74!
 
Portal vein, 653
 
Postanal gut of Elasmobranchii, 58, 59,
60; Teleostei, 75; Chick, 169; general account of, 323, 772
 
Prsemaxilla, 594
 
Praeopercular bone, 593
 
Prrcoral lobe, ganglion of, 377, 380
 
Prefrontals, 597
 
Presphenoid region of skull, 570
 
Primitive groove of Chick, 1 55
 
 
 
790
 
 
 
INDEX.
 
 
 
Primitive streak, of Chick, 152, 161;
meaning of, 153; origin of mesoblast
form in Chick, 154; continuity of
hypoblast with epiblast at anterior end
of, in Chick, 156; comparison of with
blastopore, 165 ; fate of, in Chick, 165 ;
of Lacerta, 203; of Rabbit, 221; of
Guinea-pig, 223 ; fusion of layers at, in
Rabbit, 224; comparison of with blastopore of lower forms, 226, 287 ; of
Mammalia, 290
 
Processus falciformis of Ammoccetes, 498 ;
of Elasmobranch, 502 ; of Teleostei , 503
Proctodseum, 778
 
Pronephros, of Teleostei, 78, 701 ; Petromyzon, 95, 99, 700; Acipenser, 106,
no; Amphibia, 134, 707; general account of, 689 ; of Cyclostomata, 700 ;
of Myxine, 701 ; Ganoidei, 705 ; of
Amniota, 714; of Chick, 718; summary of and general conclusions as to,
728; relation of, to mesonephros, 731 ;
cause of atrophy of, 729
Prootic, 596, 597
Propterygium, 616
Proteus, branchial arches of, 142
Protochordata, characters of, 327
Protoganoidei, characters of, 328
Protognathostomata, characters of, 328
Protopentadactyloidei, characters of, 329
Protovertebrata, characters of, 328
Pseudis, Tadpole of, 139; vertebral
 
column of, 556
 
Pseud ophryne, yolk-sack of, 140; Tadpole of, 140
Pterygoid bone, of Teleostei, 581; origin
 
of, 597
 
Pterygoquadrate bar, of Elasmobranchii,
576; of Teleostei, 581; Axolotl, 584;
F r g, 584; ofSauropsida, 588; of Mammalia, 589
 
Pulmonary artery, origin of, 645 ; of
Amphibia, 645 ; of Amniota, 649
 
Pulmonary vein, 655
 
Pupil, 489
 
Pyrosoma, development of, 23
 
Quadrate bone of Teleostei, 581 ; of
Axolotl, 584; Frog, 585; Sauropsida,
588
 
Quadratojugal bone, 594
 
Rabbit, development of, 214; general
growth of embryo of, 227 ; placenta of,
248
 
Radiate symmetry, passage from to bilateral symmetry, 373 376
 
Raja, caudal vertebras of, 553
 
Rat, placenta of, 242
 
Recessus labyrinthi, 519
 
Reissner's membrane, 524
 
Reptilia, development of, 202; viviparous,
202; cerebellum of, 426; infundibulum
of, 431; pituitary body of, 436; cerebrum of, 439; vertebral column of,
 
 
 
556; arterial system of, 648; venous
system of, 656; mesonephros of, 713;
testicular network of, 723; spermatozoa
of, 747
 
Restiform tracts of Elasmobranchii and
Teleostei, 425
 
Retina, histogenesis of, 490
 
Retinulse, 482
 
Rhabdom, 482
 
Rhinoderma, brood-pouch of, 121; metamorphosis of, 1 39
 
Ribs, development of, 560
 
Roseniniiller's organ, 725
 
Rotifera, excretory organs of, 680
 
Round ligament of liver, 663
 
Ruminantia, placenta of, 253
 
Sacci vasculosi, 437
 
Sacculus hemisphericus, 519; of Mammals, 519, 520
 
Sagitta. See ' Chaetognatha'
 
Salpa, sexual development of, 29; asexual
development of, 33
 
Salamandra, larva of, 142; vertebral
column of, 553; limbs of, 619; mesonephros of, 708; Miillerian duct of,
710
 
Salmonidse, hypoblast of, 71; generative
ducts of, 704
 
Sauropsida, gastrula of, 286; meaning of
primitive streak of, 288; blastopore of,
289 ; mandibular and hyoid arches of,
588 ; pectoral girdle of, 60 1
 
Scala, vestibuli, 522; tympani, 523;
media, 522
 
Scales, general development of, 396 ; development of placoid scales, 395
 
Scapula, 599
 
Sclerotic, 488
 
Scrotum, development of, 727
 
Scyllium, caudal vertebrse of, 553; mandibular and hyoid arches of, 578; pectoral girdle of, 600; limbs of, 610; pelvic fin of, 614; pectoral fin of, 615
 
Segmental duct, 690 ; development of in
Elasmobranchs, 690; of Cyclostomata,
700; of Teleostei, 701; of Ganoidei,
704, 705 ; of Amphibia, 707 ; of Amniota, 713
 
Segmental organs, 682
 
Segmental tubes, 690 ; development of in
Elasmobranchs, 691 ; rudimentary anterior in Elasmobranchs, 693 ; development of secondary, 731
 
Segmentation cavity, of Elasmobranchii,
42 44; Teleostei, 69, 85, 86; Amphibia, 122, 125
 
Segmentation, meaning of, 331
 
Segmentation of ovum, in Amphioxus, 2 ;
Ascidia, 9 ; Molgula, 22 ; Pyrosoma,
23; Salpa, 30; Elasmobranchii, 40;
Telostei, 69; Petromyzon, 84; Acipenser, IOT, Lcpidosteus, in; Amphibia, 122, 124; Newt, 125; Chick,
146; Lizard, 202: Rabbit, 214
 
 
 
INDEX.
 
 
 
791
 
 
 
Semicircular canals, 519
 
Sense organs, comparative account of
development of, 304
 
Septum lucidum, 443
 
Serous membrane, Lacerta, 209; of Rabbit, 237
 
Seventh nerve, development of, 459
 
Shell-gland of Crustacea, 689
 
Shield, embryonic, of Chick, 151 ; of
Lacerta, 202
 
SimiadiK, placenta of, 247
 
Sinus rhomboidalis, of Chick, 162
 
Sinus venosus, 637
 
Sirenia, placenta of, 255
 
Sixth nerve, 463
 
Skate, mandibular and hyoid arches of,
 
577
 
Skeleton, elements of found in Vertebrata, 542
 
Skull, general development of, 564 ; historical account of, 564 ; development of
cartilaginous, 566; cartilaginous walls
of, 570; composition of primitive cartilaginous cranium, 565
 
Somatopleure, of Chick, 170
 
Spelerpes, branchial arches of, 142
 
Spermatozoa, of Porifera, 741; of Vertebrata, 746
 
Sphenoid bone, 595
 
Sphenodon, hyoid arch of, 588
 
Spinal cord, general account of, 415;
white matter of, 415; central canal of,
417, 418; commissures of, 417; grey
matter of, 417; fissures of, 418
 
Spinal nerves, posterior roots of, 449;
anterior roots of, 453
 
Spiracle, of Elasmobranchii, 62 ; Acipenser, 105; Amphibia, 136
 
Spiral valve. See 'Valve'
 
Spleen, 664
 
Splenial bone, 595
 
Squamosal bone, 593
 
Stapes, 529; of Mammal, 590
 
Sternum, development of, 562
 
Stolon of Doliolum, 29 ; Salpa, 33
 
Stomodaeum, 774
 
Stria vascularis, 524
 
Styloid process, 591
 
Sub-intestinal vein, 65 1 ; meaning of,
 
651
 
Syngnathus, brood-pouch of, 68
Subnotochordal rod, of Elasmobranchii,
 
54; Petromyzon, 94; Acipenser, no;
 
Lepidosteus, 115; general account of,
 
754; comparison of with siphon of
 
Chsetopods, 756
 
Subzonal membrane, 237; villi of, 236
Sulcus of Munro, 432
Supraclavicle, 600
Suprarenal bodies, 664
Supra-temporal bone, 593
Swimming bladder, see Air bladder
Sylvian aqueduct, 428
Sylvian fissure, 444
Sympathetic ganglia, development of, 467
 
 
 
Tadpole, 134, 139, 140; phylogenetic
meaning of, 137; metamorphosis of,
137; m can ing of suctorial mouth of, 585
 
Tail of Teleostei, 80; Acipenser, 109;
Lepidosteus, 109; Amphibia, 132
 
Tarsus, development of, 620
 
Teeth, horny provisional, of Amphibia,
136; general development of, 776;
origin of, 777
 
Teleostei, development of, 68; viviparous, 68; comparison of formation of
layers in, 286; restiform tracts of, 425 ;
mid-brain of, 425 ; infundibulum of,
431 ; cerebrum of, 439; nares of, 534;
lateral line of, 538; notochord and
membrana elastica of, 549 ; vertebral
column of, 553; ribs of, 561; hyoid
and mandibular arches of, 579; pectoral girdle of, 601 : pelvic girdle of,
606; limbs of, 618; heart of, 637;
arterial system of, 645; muscle-plates
of, 670; excretory organs of, 701 ; generative ducts of, 704, 735, 749; swimming bladder of, 763 ; postanal gut of,
 
Teredo, nervous system of, 414
 
Test of Ascidia, 14; Salpa, 31
 
Testicular network, of Elasmobranchs,
697 ; of Amphibia, 712 ; Reptilia, 723 ;
of Mammals, 724
 
Testis of Vertebrata, 746
 
Testis, connection of with Wolffian body,
in Elasmobranchii, 697; in Amphibia,
710; in Amniota, 723; origin of, 735
 
Thalamencephalon of Chick, 175; general development of, 430
 
Third nerve, development of, 461
 
Thymus gland, 762
 
Thyroid gland, Petromyzon, 92 ; general
account of, 759; nature of, 760; development of in Vertebrata, 761
 
Tooth. See 1 Teeth'
 
Tori semicirculares, 428
 
Tornaria, 372
 
Trabeculas, 565, 567; nature of, 568
 
Trachea, 766
 
Trematoda, excretory organs of, 68 1
 
Triton alpestris, sexual larva of, 143
 
Triton, development of limbs of, 619}
urinogenital organs of, 7 12
 
Truncus arteriosus, 638; of Amphibia,
638; of Birds, 639
 
Turiicata, development of mesoblast of,
293; test of, 394; eye of, 507; auditory organ of, 530; olfactory organ of,
532; generative duct of, 749 ; intestine
of, 767; postanal gut of, 771; stomodseum of, 775
 
Turbellaria, excretory organs of, 68 1
 
Tympanic annulus of *'rog, 587
 
Tympanic cavity, of Amphibia, 135;
Chick, 1 80; Rabbit, 232; general development of, 528; of Mammals, 591
 
Tympanic membrane, of Chick, 180;
general development of, 528
 
 
 
792
 
 
 
INDEX.
 
 
 
Tympanohyal, 591
 
Umbilical canal of Elasmobranchii, 54,
 
57, 58, 59
 
Umbilical cord, 238; vessels of, 239
 
Ungulata, placenta of, 250
 
Urachus, 239, 726
 
Ureters, of Elasmobranchii, 696; development of, 723
 
Urethra, 727
 
Urinary bladder of Amphibia, "Jii; of
Amniota, 726
 
Urinogenital organs, see Excretory organs
 
Urinogenital sinus of Petromyzon, 700;
of Sauropsida, 726; of Mammalia,
727
 
Urochorda, development of, 9
 
Uterus, development of, 726; of Marsupials, 726
 
Uterus masculinus, 726
 
Utriculus, 519
 
Uvea of iris, 489
 
Vagus nerve, development of, 456, 457;
intestinal branch of, 458; branch of to
lateral line, 459
 
Valve, spiral, of Petromyzon, 97; Acipenser, no; general account of, 767
 
Valves, semilunar, 641; auriculo-ventricular, 642
 
Vasa efferentia, of Elasmobranchs, 697 ;
of Amphibia, 711; general origin of,
724
 
Vascular system, of Amphioxus, 8; Petromyzon, 97; Lepidosteus, 116; general
development of, 632
 
Vas deferens, of Elasmobranchii, 697 ;
of Amniota, 723
 
Vein, sub-intestinal of Petromyzon, 97 ;
Acipenser, no; Lepidosteus, 116
 
Velum of Petromyzon, 9 1
 
Vena cava inferior, development of, 655
 
Venous system of Petromyzon, 97; general development of, 651; of Fishes,
651 ; of Amphibia and Amniota, 655 ;
of Reptilia, 656; of Ophidia, 656; of
Aves, 658; of Mammalia, 661
 
Ventricle, fourth, of Chick, 176; history
of, 424
 
Ventricle, lateral, 438, 440; fifth, 443
 
Ventricle, third, of Chick, 175
 
Vertebral bodies, of Chick, 183
 
Vertebral column, development of, 545,
549; epichordal and perichordal development of in Amphibia, 556
 
Vespertilionidse, early development of,
217
 
Vieussens, valve of, 426
 
Villi, placental, of zona radiata, 235 ;
subzonal membrane, 235; chorion, 237;
 
 
 
Man, 246; comparative account of,
2 575 of young human ovum, 265, 269
 
Visceral arches, Amphioxus, 7 ; Elasmobranchii, 57 60; Teleostei, 77; Acipenser, 1 06; Lepidosteus, 116; Amphibia, 133; Chick, 177; Rabbit,
231; prseoral, 570; relation of to head
cavities, 572; disappearance of posterior, 573; dental plates of in Teleostei, 574
 
Visual organs, evolution of, 470
 
Vitelline arteries of Chick, 195
 
Vitelline veins of Chick, 195
 
Vitreous humour, of Ammoccetes, 98 ;
general development of, 494; blood*
vessels of in Mammals, 503 ; mesoblastic ingrowth in Mammals, 503
 
Vomer, 594
 
White matter, of spinal cord, 415; of
brain, 423
 
Wolffian body, see ' Mesonephros '
 
Wolffian duct, first appearance of in
Chick, 183; general account of, 690;
of Elasmobranchs, 693 ; of Ganoids,
704; of Amphibia, 710; of Amniota,
713; atrophy of in Amniota, 724
 
Wolffian ridge, 185
 
Yolk blastopore, of Elasmobranchii, 64
 
Yolk, folding off of embryo from, in
Elasmobranchii, 55; in Teleostei, 76;
Acipenser, 106; Chick, 168, 170
 
Yolk nuclei, of Elasmobranchii, 41, 53;
Teleostei, 69, 75
 
Yolk, of Elasmobranchii, 40; Teleostei,
68; Petromyzon, 96; Acipenser, 109;
Amphibia, 122, 129; Chick, 146; influence of on formation of layers, 278;
influence of on early development,
 
341, 342
 
Yolk-sack, Amphibia, 131, 140, 141; enclosure of, 123
 
.Yolk-sack, development of in Rabbit,
227; of Mammalia reduced, 227; circulation of in Rabbit, 233 ; enclosure
of in Sauropsida, 289
 
Yolk-sack, enclosure of, Petromyzon, 86
 
Yolk-sack, Lepidosteus, 118
 
Yolk-sack of Chick, enclosure of, 160;
stalk of, 174; general account of, 193;
circulation of, 195 ; later history of, 198
 
Yolk-sack of Elasmobranchii, enclosure
of, 62, 283; circulation of, 64
 
Yolk-sack of Lacerta, 209 ; circulation of,
209
 
Yolk-sack, Teleostei, 75, 81; enclosure
of, 75 ; circulation of, 81
 
Zona radiata, villi of, 237
Zonula of Zinn, 495
 
 
 
BIBLIOGRAPHY.
 
 
 
CEPHALOPODA.
 
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UROCHORDA.
 
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B. Hi. a
 
 
 
BIBLIOGRAPHY.
 
 
 
(24) A. Krohn. "Ueber die Entwicklung d. Ascidien." Mailer's Archiv,
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(33) H. Milne-Edwards. "Observations s. 1. Ascidies composees des cotes de
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(36) W. Salensky. "Ueber die Entwicklung d. Hoden u. iiber den Generationswechsel d. Salpen." Zeit.f. wiss. Zool., Bd. xxx. Suppl. 1878.
 
(37) C. Semper. " Ueber die Entstehung d. geschichteten Cellulose-Epidermis
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(38) Fr. Todaro. Sopra lo sviluppo e F anatomia delle Salpc. Roma, 1875.
 
(39) Fr. Todaro. "Sui primi fenomeni dello sviluppo delle Salpe." Realc
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ELASMOBRANCHII.
 
(40) F. M. Balfour. " A preliminary account of the development of the Elasmobranch Fishes." Quart. J. of Micr. Science, Vol. xiv. 1876.
 
(41) F. M. Balfour. "A Monograph on the development of Elasmob ranch
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(42) Z. Gerbe. " Recherches sur la segmentation de la cicatrule et la formation
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(43) W. His. " Ueb. d. Bildung v. Haifischenembryonen." Zeit. fur Anat. u.
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(44) A. Kowalevsky. "Development of Acanthias vulgaris and Mustelus
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BIBLIOGRAPHY.
 
 
 
Ill
 
 
 
(52) C. Semper. "Die Stammesverwandschaft d. Wirbelthiere u. Wirlwllosen. Arbeit, a. d. zool.-zoot. Instit. Wiirzburg, Vol. II. 1875.
 
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TELEOSTEI.
 
(55) Al. Agassiz. " On the young Stages of some Osseous Fishes. I. Development of the Tail." Proceedings of the American Academy of Arts and Sciences,
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LXXIV.
 
(59)
 
Osseux. '
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(60)
 
 
 
E. v. Beneden. "A contribution to the history of the Embryonic development of the Teleosteans." Quart. J. of Micr. Sci., Vol. xvm. 1878.
 
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(62) A. Gotte. "Beitrage zur Entwicklungsgeschichte der Wirbelthiere."
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(72) T. Oellacher. " Beitrage zur Entwicklungsgeschichte der Knochenfische
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a 2
 
 
 
BIBLIOGRAPHY.
 
 
 
CYCLOSTOMATA.
 
(77) E. Calberla. " Der Befruchtungsvorgang beim Petromyzon Planeri."
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(78) E. Calberla. "Ueb. d. Entwicklung d. Medullarrohres u. d. Chorda
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(79) C. Kupffer u. B. Benecke. Der Vorgang d. Befruchtimg am Ei d.
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(80) Aug. Muller. " Ueber die Entwicklung d. Neunaugen." Miiller s
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(81) Aug. Muller. Beobachtungen iib. d. Befruchtungserscheinungen im Ei d.
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(82) W. Muller. "Das Urogenitalsystem d. Amphioxus u. d. Cyclostomen. '
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(83) Ph. Owsjannikoff. "Die Entwick. von d. Flussneunaugen. " ^ Vorlauf.
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(84) Ph. Owsjannikoff. On the development of Petromyzon fiuviatihs
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(85) Anton Schneider. Beitrdge z. vergleich. Anat. a. Entwick. d. Wirbelthiere. Quarto. Berlin, 1879.
 
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(87) W. B. Scott. " Vorlaufige Mittheilung iib. d. Entwicklungsgeschichte d.
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BIBLIOGRAPHY,
 
 
 
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vi BIBLIOGRAPHY.
 
 
 
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REPTILIA.
 
(154) C. Kupffer and Benecke. Die erste Entwicklung am Ei d. Keptilien.
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BIBLIOGRAPHY, vii
 
 
 
(155) C. Kupffer. "Die Entstehung d. Allantois u. <1. Gastrula d. Wirbclthiere." Zoologischer Anzeiger, Vol. II. 1879, pp. 520, 593, 612.
 
Lacertilia.
 
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Ophidia.
 
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Chelonia.
 
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Crocodilia.
 
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MAMMALIA.
 
(168) K. E. von Baer. Ueb. Entwicklungsgcschichte d. Jhiere. Konigsberg,
 
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viii BIBLIOGRAPHY.
 
 
 
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(191) John Anderson. Anatomical and Zoological Researches in Western
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(202) Th. H. Huxley. The Elements of Comparative Anatomy. London,
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BIBLIOGRAPHY.
 
 
 
IX
 
 
 
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(214) R.Owen. On the Anatomy of Vertebrates, Vol. III. London, 1868.
 
(215) G. Rolleston. " Placental structure of the Tenrec, etc." Transactions
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(218) W. Turner. "On the placentation of Sloths (Cholcepus Hoffrnanni)."
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Human Embryo.
 
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(234) W. Krause.
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(235) W. Krause.
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Zeit.
 
 
 
X BIBLIOGRAPHY.
 
 
 
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(247) R. Remak. Untersuchungen iib. d. Entiuicklung d. Wirbelthiere, 1850
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(251) E. Haeckel. Schb'pfungsgeschichte. Leipzig. Vide also Translation.
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(252) E. Haeckel. Anthropogenie. Leipzig. Vide also Translation. Antliropogeny. Kegan Paul and Co., London, 1878.
 
(253) A. Kowalevsky. " Entwicklungsgeschichte d. Amphioxus lanceolatus."
Mem. Acad. d. Scien. St Petersbourg, Ser. VII. Tom. xi. 1867, and Archiv f. ?nikr.
Anat., Vol. XIII. 1877.
 
(254) A. Kowalevsky. "Weitere Stud. lib. d. Entwick. d. einfachen Ascidien."
Archiv f. mikr. Anat., Vol. VII. 1871.
 
(255) C. Semper. "Die Stammesverwandschaft d. Wirbelthiere u. Wirbellosen." Arbeit, a. d. zool.-zoot. Instit. Wiirzburg, Vol. u. 1875.
 
(256) C. Semper. "Die Verwandschaftbeziehungen d. gegliederten Thiere."
Arbeit, a. d. zool.-zoot. Instit. Wiirzburg, Vol. in. 1876 1877.
 
GENERAL WORKS ON EMBRYOLOGY.
 
(257) Allen Thomson. British Association Address, 1877.
 
(258) A. Agassiz. "Embryology of the Ctenophoroe." Mem. Amcr. Acad. of
Arts and Sciences, Vol. X. 1874.
 
(259) K. E. von Baer. Ueb. Entivicklnngsgeschichle d. Thiere. Konigsberg,
18281837.
 
 
 
BIBLIOGRAPHY.
 
 
 
XI
 
 
 
(260) F. M. Balfour. "A Comparison of the Early Stages in the Development
of Vertebrates." Qttart. Journ. of Micr. Set., Vol. XV. 1875.
 
 
 
(261)
1874.
 
 
 
C. Glaus. Die Typenlehre u. E. HaeckeFs sg. Gastnca-theorie. Wieii,
 
 
 
(262) C. Claus. Grundziige d. Zoologie. Marburg und Leipzig, 1879.
 
(263) A. Dohrn. Der Ursprung d. Wirbdlhiere u. d. Princip des Functionswechsds. Leipzig, 1875.
 
(264) C. Gegenbaur. Grundriss d. vergleichenden Anatomic. Leipzig, 1878.
Vide also Translation. Elements of Comparative Anatomy. Macmillan Co.
1878.
 
(265) A. Gotte. Ent^vicklungsgeschichte d. Unke. Leipzig, 1874.
 
(266) E. Haeckel. Studien z. Gastrcca-theorie, Jena, 1877; anc ' a ' so Jenaische
Zeitschrift, Vols. vm. and IX. 1874-5.
 
(267) E. Haeckel. Schdpfungsgeschichte. Leipzig. Vide also Translation,
The History of Creation. King & Co., London, 1878.
 
(268) E. Haeckel. Anthropogenic. Leipzig. Vide also Translation, Atithropogeny. Kegan Paul & Co., London, 1878.
 
(269) B. Hatschek. "Studien lib. Entwicklungsgeschichte d. Anneliden."
Arbeit, a. d. zool. Instit. d. Univer. Wien. 1878.
 
(270) O. and R. Hertwig. " Die Actinien." Jenaische Zeitschrift, Vols. xiil.
and XIV. 1879.
 
(271) O. and R. Hertwig. Die Cctlomtheorie. Jena, 1881.
 
(272) O. Hertwig. Die Chatognathen. Jena, 1880.
 
(273) R. Hertwig. Ueb. d. Ban d. Ctenophoren. Jena, 1880.
 
(274) T. H. Huxley. The Anatomy of Invertebrated Animals. Churchill,
1877.
 
(274*) T. H. Huxley. "On the Classification of the Animal Kingdom."
Quart. J. of Micr. Science, Vol. XV. 1875.
 
(275) N. Kleinenberg. Hydra, eine anatomisch-entivicklungsgeschichte Untersnchung. Leipzig, 1872.
 
(276) A. Kolliker. Entwicklungsgeschichte d. Menschen u. d. hbh. Thiere.
Leipzig, 1879.
 
(277) A. Kowalevsky. " Embryologische Studien an Wurmern u. Arthropoden."
Mem. Acad. Petersbourg, Series vii. Vol. xvi. 1871.
 
(278) E. R. Lankester. "On the Germinal Layers of the Embryo as the
Basis of the Genealogical Classification of Animals." Ann. and Mag. of Nat. Hist.
 
1873
(279) E. R. Lankester. " Notes on Embryology and Classification." Quart.
 
Jotirn. of Alter. Set., Vol. xvn. 1877.
 
(280) E. Metschnikoff. "Zur Entwicklungsgeschichte d. Kalkschwamme."
Zeit. f. wiss. Zool., Vol. xxiv. 1874.
 
(281) E. Metschnikoff. " Spongiologische Studien." Zeit. f. wiss. Zool.,
Vol. xxxn. 1879.
 
(282) A. S. P. Packard. Life Histories of Animals, including Man, or Outlines
of Comparative Embryology. Holt and Co., New York, 1876.
 
(283) C. Rabl. " Ueb. d. Entwick. d. Malermuschel. " Jenaische Zeitsch., Vol.
x. 1876.
 
(284) C. Rabl. "Ueb. d. Entwicklung. d. Tellerschneke (Planorbis)." Morph.
Jahrbuch, Vol. v. 1879.
 
(285) H. Rathke. Abhandhmgen z. Bildung und Enlwicklungsgesch.d. Menschen
u. d. Thiere. Leipzig, 1833.
 
(286) H. Rathke. Ueber die Bildung u. Entwicklungs. d. Flusskrebses. Leipzig,
1829.
 
(287) R. Remak. Untersuch. ilb. d. Entwick. d. Wirbelthiere. Berlin, 1855.
 
(288) Salensky. " Bemerkungen lib. Haeckels Gastrsea-theorie." Archiv /.
Naturgeschichte, 1874.
 
(289) E. Schafer. "Some Teachings of Development." Quart. Jotint. of Micr.
Science, Vol. xx. 1880.
 
(290) C. Semper. " Die Verwandtschaftbeziehungen d. gegliederten Thiere."
Arbeiten a. d. zool.-zoot. Instit. Wiirzburg, Vol. in. 1876-7.
 
 
 
Xll BIBLIOGRAPHY.
 
 
 
GENERAL WORKS DEALING WITH THE DEVELOPMENT OF
THE ORGANS OF THE CHORDATA.
 
(291) K. E. von Baer. Ueber Enlwicklungsgeschichte d. Thiere. Konigsberg,
! 828 1837.
 
(292) F. M. Balfour. A Monograph on the development of Elasmobranch Fishes.
London, 1878.
 
(293) Th. C. W. Bischoff. Entwicklungsgesch. d. Siiugdhiere u. d. Menschen.
Leipzig, 1842.
 
(294) C. Gegenbaur. Grundriss d. vergleichenden Anatomic. Leipzig, 1878.
Vide also English translation, Elements of Comp. Anatomy. London, 1878.
 
(295) M. Foster and F. M. Balfour. The Elements of Embryology. Part I.
London, 1874.
 
(296) Alex. Gotte. Entwickhmgsgeschichte d. Unke. Leipzig, 1875.
 
(297) W. His. Untersuch. ilb. d. erste Anlage d. Wirbelthierleibes. Leipzig,
1868.
 
(298) A. K 6 Hiker. Entwickhmgsgeschichte d. Menschen u. der hoheren Thiere.
Leipzig, 1879.
 
(299) H. Rathke. Abhandlungen u. Bildung und Entwickhingsgeschichle d.
Menschen u. d. Thiere. Leipzig, 1838.
 
(300) H. Rathke. Entwicklungs. d. Natter. Konigsberg, 1839.
 
(301) H. Rathke. Entwicklungs. d. Wirbelthiere. Leipzig, 1861.
 
(302) R. Remak. Untersuchungen iib. d. Entwicklung d. Wirbelthiere. Berlin,
18501855.
 
(303) S. L. Schenk. Lehrbuch d. vergleich. Embryologie d. Wirbelthiere.
Wien, 1874.
 
. EPIDERMIS AND ITS DERIVATIVES.
General.
 
(304) T. H. Huxley. " Tegumentary organs." Todd's Cyclopedia of Anat.
and Physiol.
 
(305) P. Z. Unna. "Histol. u. Entwick. d. Oberhaut." Archiv /. mikr. Anat.
Vol. XV. 1876. Pft&also Kolliker (No. 298).
 
Scales of the Pisces.
 
(306) O. Hertwig. "Ueber Bau u. Entwicklung d. Placoidschuppen u. d.
Zahne d. Selachier." Jenaische Zeitschrift, Vol. vill. 1874.
 
(307) O. Hertwig. " Ueber d. Hautskelet d. Fische." Morphol. Jahrbuch,
Vol. u. 1876. (Siluroiden u. Acipenseridae.)
 
(308) O. Hertwig. "Ueber d. Hautskelet d. Fische (Lepidosteus u. Polypterus)." Morph. Jahrbuch, Vol. v. 1879.
 
Feathers.
 
(309) Th. Studer. Die Entwick. d. Federn. Inaug. Diss. Bern, 1873.
 
(310) Th. Studer. " Beitrage z. Entwick. d. Feder." Zeit.f. wiss. Zool., Vol.
xxx. 1878.
 
Sweat-glands.
 
(311) M. S. Ranvier. " Sur la structure des glandes sudoripares." Comptes
Rendus, Dec. 29, 1879.
 
 
 
BIBLIOGRAPHY. xiii
 
 
 
Mammary glands.
 
(312) C. Creighton. "On the development of the Mamma and the Mammary
function." Jour, of Anat. and Phys. , Vol. xi. 1877.
 
(313) C. Gegenbaur. " Bemerkungen lib. d. Milchdriisen-Papillen d. Saugethiere." Jenaische Zeit.. Vol. VII. 1873.
 
(314) M. Huss. " Beitr. z. Entwick. d. Milchdriisen b. Menschen u. b. Wiederkauern." Jenaische Zeit., Vol. vil. 1873.
 
(315) C. Langer. " Ueber d. Bau u. d. Entwicklung d. Milchdriisen." Denk.
d. k. Akad. Wiss. Wien, Vol. in. 1851.
 
THE NERVOUS SYSTEM.
Evolution of the Nervous System.
 
(316) F. M. Balfour. " Address to the Department of Anat. and Physiol. of the
British Association." 1880.
 
(317) C. Claus. "Studien lib. Polypen u. Quallen d. Adria. I. Acalephen,
Discomedusen." Denk. d. math.-natiirwiss. Classe d. k. Akad. Wiss. Wien, Vol.
xxxvin. 1877.
 
(318) Th. Eimer. Zoologische Studien a. Capri. I. Ueber Beroe ovatus. Ein
Beitrag z. Anat. d. Rippenquallen. Leipzig, 1873.
 
(319) V. Hensen. " Zur Entwicklung d. Nervensystems. " Virchow's Archiv,
Vol. xxx. 1864.
 
(320) O. and R. Hertwig. Das Nerven system u. d. Sinnesorgane d. Medusen.
Leipzig, 1878.
 
(321) O. and R. Hertwig. "Die Actinien anat. u. histol. mit besond. Beriicksichtigung d. Nervenmuskelsystem untersucht." Jenaische Zeit., Vol. xiii. 1879.
 
(322) R. Hertwig. "Ueb. d. Bau d. Ctenophoren." Jenaische Zeitschrift,
Vol. xiv. 1880.
 
(323) A. W. Hubrecht. "The Peripheral Nervous System in Palseo- and
Schizonemertini, one of the layers of the body-wall." Quart, y. of Micr. Science,
Vol. xx. 1880.
 
(324) N. Kleinenberg. Hydra, eine anatomisch-entwickhmgsgeschichthche Untersuchung. Leipzig, 1872.
 
(325) A. Kowalevsky. " Embryologische Studien an Wtirmern u. Arthropoden." Mem. Acad. Petersboiirg, Series vil., Vol. XVI. 1871.
 
(326) E. A. Schafer. "Observations on the nervous system of Aurelia aurita."
Phil. Trans. 1878.
 
Nervous System of the Invertebrata.
 
(327) F. M. Balfour. "Notes on the development of the Araneina." Quart.
J. of Micr. Science, Vol. xx. 1880.
 
(328) B. Hatschek. "Beitr. z. Entwicklung d. Lepidopteren.' Jenaische
Zeitschrift, Vol. XI. 1877.
 
(329) N. Kleinenberg. "The development of the Earthworm, Lumbncus
Trapezoides." Quart. J. of Micr. Science, Vol. xix. 1879.
 
(330) A. Kowalevsky. "Embryologische Studien an Wiirmern u. Arthropoden." Mem. Acad. Petersbourg, Series vin., Vol. xvi. 1871.
 
(331) H. Reichenbach. "Die Embryonalanlage u. erste Entwick. d. Flusskrebses." Zeit.f. wiss. Zool, Vol. xxix. 1877.
 
Central Nervous System of the Vertebrata.
 
(332) C. J. Carus. Versuch einer Darstellung d. Nervensystems, etc. Leipzig,
 
(333) J. L. Clark. " Researches on the development of the spinal cord in Man,
Mammalia and Birds." Phil. Trans., 1862.
 
 
 
xiv BIBLIOGRAPHY.
 
 
 
(334) E. Dursy. " Beitrage zur Entwicklungsgeschichte des Hirnanhanges. "
Centralblatt f. d. med. \Vissenschaften, 1 868. Nr. 8.
 
(335) E. Dursy. Zur Entwicklungsgeschichte des Kopfes des Menschen und der
hb'heren Wirbelthiere. Tiibingen, 1869.
 
(336) A. Ecker. "Zur Entwicklungsgeschichte der Furchen und Windungen
der Grosshirn-Hemispharen im Foetus des Menschen." Archiv f. Anthropologie, v.
Ecker und Lindenschmidt. Vol. ill. 1868.
 
(337) E. Ehlers. " Die Epiphyse am Gehirn d. Plagiostomen." Zeit.f.wiss.
Zool. Vol. xxx., suppl. 1878.
 
(338) P. Flechsig. Die Leitungsbahnen im Gehirn und Riickenmark des
Menschen. Auf Grtind entwicklungsgeschichtlicher Untersuchungen. Leipzig, 1876.
 
(339) V. Hensen. "Zur Entwicklung des Nervensystems." Virchoisfs Archiv,
Bd. xxx. 1864.
 
(340) L. Lowe. " Beitrage z. Anat. u. z. Entwick. d. Nervensystems d. Saugethiere u. d. Menschen." Berlin, 1880.
 
(341) L. Lowe. " Beitrage z. vergleich. Morphogenesis d. centralen Nervensystems d. Wirbelthiere." Mitthcil. a. d. embryol. Instit. Wien, Vol. u. 1880.
 
(342) A. M. Marshall. "The Morphology of the Vertebrate Olfactory organ."
Quart. J. of Micr. Science, Vol. xix. 1879.
 
(343) V. v. Mihalkovics. Entwicklungsgeschichte d. Gehirns. Leipzig, 1877.
 
(344) W. Miiller. " Ueber Entwicklung und Bau der Hypophysis und des
Processus infundibuli cerebri. " Jenaische Zeitschrift. Bd. vi. 1871.
 
(345) H. Rahl- Ruck hard. "Die gegenseitigen Verhaltnisse d. Chorda,
Hypophysis etc. bei Haifischembryonen, nebst Bemerkungen lib. d. Deutung d.
einzelnen Theile d. Fischgehirns." Morphol. Jahrbuch, Vol. vi. 1880.
 
(346) H. Rathke. " Ueber die Entstehung der glandula pituitaria. " Mullens
Archiv f. Anat. und Physiol. , Bd. V. 1838.
 
(347) C. B. Reich ert. Der Bau des menschlichen Gehirns. Leipzig, 1859 u 1861.
 
(348) F. Schmidt. "Beitrage zur Entwicklungsgeschichte des Gehirns."
Zcitschrift f. wiss. Zoologie, 1862. Bd. xi.
 
(349) G. Schwalbe. "Beitrag z. Entwick. d. Zwischenhirns." Sitz. d.
Jenaischen Gesell.f. Med. u. Natttnviss. Jan. 23, 1880.
 
(350) Fried. Tiedemann. Anatomie und Bildungsgeschichte des Gehirns im
Foetus des Menschen. Niirnberg, 1816.
 
Peripheral Nervous System of the Vertebrata.
 
(351) F. M. Balfour. "On the development of the spinal nerves in Elasmobranch Fishes." Philosophical Transactions, Vol. CLXVI. 1876; vide also, A monograph on the development of Elasmobranch Fishes. London, 1878, pp. 191216.
 
(352) W. His. " Ueb. d. Anfiinge d. peripherischen Nervensystems." Archiv
f. Anat. u. Physiol., 1879.
 
(353) A. M. Marshall. " On the early stages of development of the nerves in
Birds." Jottrnal of Anat. and Fkys.,Vo\. XI. 1877.
 
(354) A. M. Marshall. "The development of the cranial nerves in the Chick."
Quart, y. of Micr. Science, Vol. xvni. 1878.
 
(355) A. M. Marshall. "The morphology of the vertebrate olfactory organ."
Quart, y. of Micr. Science, Vol. xix. 1879.
 
(356) A. M. Marshall. " On the head-cavities and associated nerves in Elasmobranchs." Quart, y. of Micr. Science, Vol. xxi. 1881.
 
(357) C. Schwalbe. "Das Ganglion oculomotorii. " Jenaische Zeitschrift,
Vol. xni. 1879.
 
Sympathetic Nervous System.
 
(360) F. M. Balfour. Monograph on the development of Elasmobranch Fishes.
London, 1878, p. 173.
 
(361) S. L. Schenk and W. R. Birdsell. "Ueb. d. Lehre vond. Entwicklung
d. Ganglien d. Sympatheticus." Mittheil. a. d. cmbryologischen Instit. Wien. Heft
III. 1879.
 
 
 
BIBLIOGRAPHY. XV
 
 
 
THE EYE.
 
Eye of the Mollusca.
 
(362) N. Bobretzky. " Observations on the development of the Cephalopoda "
(Russian). Nachrichtcn d. kaiserlichen Gesell. d. Frennde der Natuna iss. Anthropolog.
Ethnogr. bei d. Universitdt Moskau.
 
(363) H. Grenacher. " Zur Entwicklungsgeschichte d. Cephalopoden." Zeit.
f. wiss. Zool., Bd. xxiv. 1874.
 
(364) V. Hensen. "Ueber d. Auge einiger Cephalopoden." Zeit. f. wiss.
Zool., Vol. xv. 1865.
 
(365) E. R. Lankester. " Observations on the development of the Cephalopoda." Quart. J. of Micr. Science, Vol. xv. 1875.
 
(366) C. Semper. Ueber Sehorganevon Typus d. Wirbelthicraugen. Wiesbaden,
1877.
 
Eye of the Arthropoda.
 
(367) N. Bobretzky. Development of Astacus and Palaemon. Kiew, 1873.
 
(368) A. Dohrn. " Untersuchungen lib. Bau u. Entwicklung d. Arthropoden.
Palinurus und Scyllarus. " Zeit. f. wiss. Zool., Bd. xx. 1870, p. 264 et seq.
 
(369) E. Claparede. "Morphologic d. zusammengesetzten Auges bei den Arthropoden." Zeit. f. wiss. Zool., Bd. X. 1860.
 
(370) H. Grenacher. Untersuchungen iib. d. Sehorgane d. Arthropoden.
Gottingen, 1879.
 
The Vertebrate Eye.
 
(371) J.Arnold. Beitrage zur Entwicklungsgeschichle des A uges. Heidelberg,
1874.
 
(372) Babuchin. "Beitrage zur Entwicklungsgeschichte des Auges." Wiirzliurger naturwissenschaftliche Zeitschrift, Bd. 8.
 
(373) L. Kessler. Zur Ent^vicklung d. Auges d. Wirbclthiere. Leipzig, 1877.
 
(374) N. Lieberkiihn. Ueber das Auge des Wirbelthierembryo. Cassel, 1872.
 
(375) N. Lieberkiihn. " Beitrage z. Anat. d. embryonalen Auges." Archiv
f. Anat. und Phys., 1879.
 
(376) L. Lowe. "Beitrage zur Anatomic des Auges" and "Die Histogenese
der Retina." Archiv f. mikr. Anat., Vol. xv. 1878.
 
(377) V. Mihalkowics. "Untersuchungen iiber den Kamm des Vogelauges."
Archiv f. mikr. Anat., Vol. IX. 1873.
 
(378) W. Miiller. " Ueber die Stammesentwickelung des Sehorgans der Wirbelthiere." Festgabe Carl Ludwig. Leipzig, 1874.
 
(379) S. L. Schenk. "Zur Entwickelungsgeschichte des Auges der Fische."
Wiener Sitzungsberichte, Bd. LV. 1867.
 
Accessory organs of the Vertebrate Eye.
 
(380) G. Born. "Die Nasenhohlen u. d. Thranennasengang d. Amphibien."
Morphologisches Jahrbuch, Bd. II. 1876.
 
(381) G. Born. " Die Nasenhohlen u. d. Thranennasengang d. amnioten Wirbelthiere. I. Lacertilia. II. Aves." Morphologisches Jahrbuch, Bd. V. 1879.
 
Eye of the T2tnicata,
 
(382) A. Kowalevsky. "Weitere Studien iib. d. Entwicklung d. einfachen
Ascidien." Archiv f. mikr. Anat., Vol. VII. 1871.
 
(383) C. Kupffer. "Zur Entwicklung d. einfachen Ascidien." Archiv f.
mikr. Anat., Vol. VII. 1872.
 
 
 
xvi BIBLIOGRAPHY.
 
 
 
AUDITORY ORGANS.
Auditory organs of tlie Invertebrata.
 
(384) V. Hensen. "Studien lib. d. Gehororgan d. Decapoden." Zeil.f. wiss.
Zool., Vol. xui. 1863.
 
(385) O. and R. Her twig. Das Nervensystem u. d. Sinnesorgane d. Medusen.
Leipzig, 1878.
 
Auditory organs of the Vertebrata.
 
(386) A. Boettcher. "Bau u. Entwicklung d. Schnecke." Denkschriften d.
kaiserl. Leap. Carol. Akad. d. Wissenschaft., Vol. xxxv.
 
(387) C. Hasse. Dievergleich. Morphologieu. Histologied. hciutigen Gehororgane
d. Wirbelthiere. Leipzig, 1873.
 
(388) V. Hensen. "Zur Morphologie d. Schnecke." Zeit. f, wiss. ZooI.,Vo\.
 
XIII. 1863.
 
(389) E. Huschke. "Ueb. d. erste Bildungsgeschichte d. Auges u. Ohres beim
bebrliteten Kiichlein." Isis von Oken, 1831, and Meckel's Archiv, Vol. VI.
 
(390) Reissner. De Auris internee formatione. Inaug. Diss. Dorpat, 1851.
 
Accessory parts of Vertebrate Ear.
 
(391) David Hunt. "A comparative sketch of the development of the ear and
eye in the Pig. " Transactions of the International Otological Congress, 1 876.
 
(392) W. Moldenhauer. "Zur Entwick. d. mittleren u. ausseren Ohres."
Morphol. Jahrbiich, Vol. ill. 1877.
 
(393) V. Urbantschitsch. " Ueb. d. erste Anlage d. Mittelohres u. d. Trommelfelles." Mittheil. a. d. embryol. Instit. Wien, Heft I. 1877.
 
OLFACTORY ORGAN.
 
(394) G. Born. "Die Nasenhohlen u. d. Thranennasengang d. amnioten
Wirbelthiere." Parts I. and II. Morphologisches Jahrbuch, Bd. V., 1879.
 
(395) A. Kolliker. " Ueber die Jacobson'schen Organe des Menschen."
Festschrift f. Rienecker, 1877.
 
(396) A. M. Marshall. "Morphology of the Vertebrate Olfactory Organ."
Quart. Journ. of Micr. Science, Vol. xix., 1879.
 
SENSE-ORGANS OF THE LATERAL LINE.
 
(397) F. M. Balfour. A Monograph on the development of Elasmobranch Fishes,
pp. 141 146. London, 1878.
 
(398) H. Eisig. "Die Segmentalorgane d. Capitelliden." Mitlhcil. a. d. zool.
Station zu Neapel, Vol. I. 1879.
 
(399) A. Gotte. Entwicklungsgeschichte d. Unke. Leipzig, 1875.
 
(400) Fr. Ley dig. Lehrbuch d. Histologie des Menschen u. d. Thiere. Hamm.
 
T857
(401) Fr. Ley dig. Nene Beitrdge z. anat. Kenntniss d. Haiitdecke u. IJautsinnesorgane d. Fische. Halle, 1879.
 
(402) F. E. Schulze. "Ueb. d. Sinnesorgane d. Seitenlinie bei Fischen und
Amphibien." Archiv f. mikr. Anat., Vol. vi. 1870.
 
(403) C. Semper. "Das Urogenitalsystem d. Selachier." Arbeit, a. d. zool.zoot. Instit. Wiirzburg, Vol. II.
 
(404) B. Solger. "Neue Untersuchungen zur Anat. d. Seitenorgane d. Fische."
Archiv f. mikr. Anat., Vol. xvil. and xvni. 1879 and 1880.
 
ORIGIN OF THE SKELETON.
 
(405) C. Gegenbaur. "Ueb. primare u. secundare Knochenliildung mit besonderer Beziehung auf d. Lehre von dem Primordialcranium." Jciiaischc Zeitschrifl, Vol. in. 1867.
 
 
 
BIBLIOGRAPHY. xvii
 
 
 
(406) O. Hertwig. "Ueber Bau u. Entwicklung cl. Placoidschuppcn u. d.
Ziihne d. Selachicr." Jetiaische Zeitschrift, Vol. vm. 1874.
 
(407) O. Hertwig. " Ueb. d. Zahnsystem d. Amphibien u. seine Bcdeutung
f. d. Genese d. Skelets d. Mundhohle." Archiv f. mikr. Anat., Vol. xi. Supplementheft, 1874.
 
(408) O. Hertwig. " Ueber d. Hautskelet d. Fische." Morphol. Jahrlmch,
Vol. u. 1876. (Siluroiden u. Acipenseriden.)
 
(409) O. Hertwig. "Ueber d. Hautskelet d. Fische (Lepidosteus u. I'olypterus)." Morph. Jahrbnch, Vol. v. 1879.
 
(410) A. Kolliker. "AllgemeineBetrachtungenub. die Entstehungd. knocliernen Schadels d. Wirbelthiere. " Berichle v. d. konigl. zoot. Anstalt z. \Viirzlwrg,
1849.
 
(411) Fr. Leydig. " Histologische Bemerkungen iib. d. Polypterus bichir."
Zeit.f. wiss. Zool., Vol. V. 1858.
 
(412) H. Muller. "Ueber d. Entwick. d. Knochensubstanz nebst Bemerkungen, etc." Zeit. f. wiss. Zool., Vol. IX. 1859.
 
(413) Williamson. "On the structure and development of the Scales and
Bones of Fishes." Phil. Trans., 1851.
 
(414) Vrolik. " Studien iib. d. Verknocherung u. die Knochen d. Schadels d.
Teleostier." Niederldndisches Archiv f. Zoologie, Vol. i.
 
 
 
NOTOCHORD AND VERTEBRAL COLUMN.
 
(415) Cartier. " Beitrage zur Entwicklungsgeschichte der Wirbelsaule." Zeitschrift fur wiss. Zool., Bd. xxv. Suppl. 1875.
 
(416) C. Gegenbaur. Untersuchungen zur vergleichenden Anatomic der Wirbelsaule der Amphibien und Reptilien. Leipzig, 1862.
 
(417) C. Gegenbaur. "Ueber die Entwickelung der Wirbelsaule des Lepidosteus mit vergleichend anatomischen Bemerkungen." Jenaisckc Zeitschrift, Bd. ill.
1863.
 
(418) C. Gegenbaur. "Ueb. d. Skeletgewebe d. Cyclostomen." Jenaische
Zeitschrift, Vol. v. 1870.
 
(419) Al. Gotte. "Beitrage zur vergleich. Morphol. des Skeletsystems d.
Wirbelthiere." II. "Die Wirbelsaule u. ihre Anhange." Archiv f. mikr. Anat., Vol.
xv. 1878 (Cyclostomen, Ganoiden, Plagiostomen, Chimaera), and Vol. xvi. 1879
(Teleostier).
 
(420) Hasse und Schwarck. "Studien zur vergleichenden Anatomic der
Wirbelsaule u. s. w." Hasse, Anatomische Studiett, 1872.
 
(421) C. Hasse. Das natiirliche System d. Elasmobranchier auf Grundlage d.
Bau. u. d. Entwick. ihrer Wirbelsaule. Jena, 1879.
 
(422) A. Kolliker. " Ueber die Beziehungen der Chorda dorsalis zur Bildung
der Wirbel der Selachier und einiger anderen Fische." Verhandlungen der physical,
medicin. Gesellschaft in Wiirzburg, Bd. X.
 
(423) A. Kolliker. " Weitere Beobachtungen iiber die Wirbel der Selachier
insbesondere iiber die Wirbel der Lamnoidei." Abhandhmgen der senkenbergischen
naturforschenden Gesellschaft in Frankfurt, Bd. V.
 
(424) H. Leboucq. " Recherches s. 1. mode de disparition de la corde dorsale
chez les vertebres superieurs." Archives de Biologie, Vol. I. 1 880.
 
(425) Fr. Leydig. Anatomisch-histologische Untersuchungen iiber Fische und
Reptilien. Berlin, 1853.
 
(426) Aug. Muller. "Beobachtungen zur vergleichenden Anatomic der Wirbelsaule." Miiller's Archiv. 1853.
 
(427) J. Muller. " Vergleichende Anatomic der Myxinoiden u. der Cyklostomen mit durchbohrtem Gaumen, I. Osteologie und Myologie." Abhandlungcn der
koniglichen Akademie der Wissenschaften zu Berlin. 1834.
 
(428) W. Muller. "Beobachtungen des pathologischen Instituts zu Jena, I.
Ueber den Bau der Chorda dorsalis." Jenaische Zeitschrift, Bd. VI. 1871.
 
(429) A. Schneider. Beitrage z. vergleich. Anat. u. Entwick. d. Wirbelthiere.
Berlin, 1879.
 
B. III. *
 
 
 
xviii BIBLIOGRAPHY.
 
 
 
RIBS AND STERNUM.
 
(430) C. Claus. " Beitrage z. vergleich. Osteol. d. Vertcbraten. I. Rippen u.
unteres Bogensystem." Sitz. d. kaiserl. Akad. Wiss. Wien, Vol. LXXIV. 1876.
 
(431) A. E. Fick. "Zur Entwicklungsgeschichte d. Rippen und Querfortsritze." Archiv f. Anat. und Physiol. 1879.
 
(432) C. Gegenbaur. "Zur Entwick. d. Wirbelsaule des Lepidosteus mil
vergleich. anat. Bemerk." Jenaische Zeit., Vol. III. 1867.
 
(433) A. Gotte. "Beitrage z. vergleich. Morphol. d. Skeletsystems d. Wirbelthiere Brustbein u. Schultergiirtel." Archiv f. mikr. Anat., Vol. xiv. 1877.
 
(434) C. Hasse u. G. Born. " Bcmerkungen lib. d. Morphologic d. Rippen."
Zoologischer Anzeiger, 1879.
 
(435) C.K.Hoffmann. " Beitrage z. vergl. Anat. d. Wirbelthiere." Niederliind. Archiv Zool., Vol. iv. 1878.
 
(436) W. K. Parker. " A monograph on the structure and development of the
shoulder-girdle and sternum." Ray Soc. 1867.
 
(437) H. Rathke. Ueb. d. Ban u. d. Enlivicklung d. Brustbeins d. Sanricr.
 
1853
(438) G. Ruge. " Untersuch. lib. Entwick. am Brustbeine d. Menschen."
Morphol. Jahrlmch., Vol. VI. 1880.
 
THE SKULL.
 
(439) A. Duges. "Recherches sur 1'Osteologie et la myologie des Batraciens a
leur differents ages." Paris, Mem. savans tirang. 1835, and An. Sci. Nat. Vol. I.
1834.
 
(440) C. Gegenbaur. UntersucJmngen z. vergleich. Anat. d. Wirbelthiere, III.
Heft. Das Kopfskelet d. Selachier. Leipzig, 1872.
 
(441) Giinther. Beob. iib. die Entwick. d. Gehbrorgans. Leipzig, 1842.
 
(442) O. Hertwig. " Ueb. d. Zahnsystem d. Amphibien u. seine Bedeutung f.
d. Genese d. Skelets d. Mundhohle. " Archiv f. mikr, Anat., Vol. xi. 1874, suppl.
 
(443) T. H. Huxley. "On the theory of the vertebrate skull." Proc. Royal
Soc., Vol. ix. 1858.
 
f444) T.H.Huxley. The Elements of Comparative Anatomy . London, 1869.
 
 
 
(445
(446
(447
 
 
 
T. H. Huxley. "On the Malleus and Incus." Proc. Zool. Soc.,
 
T. H. Huxley. "On Ceratodus Forsteri." Proc. Zool. Soc., 1876.
 
T. H. Huxley. " The nature of the craniofacial apparatus of Petromyzon."
 
 
 
Journ. of Anat. and Phys., Vol. X. 1876.
 
(448) T. H. Huxley. The Anatomy of Vertebrated Animals. London, 1871.
 
(449) W. K. Parker. "On the structure and development of the skull of the
Common Fowl (Gallus Domesticus). " Phil. Trans., 1869.
 
(450) W. K. Parker. "On the structure and development of the skull of the
Common Frog (Rana temporaria)." Phil. Trans., 1871.
 
(451) W. K. Parker. "On the structure and development of the skull in the
Salmon (Salmo salar)." Bakerian Lecture, Phil. Trans., 1873.
 
(452) W. K. Parker. "On the structure and development of the skull in the
Pig (Susscrofa)." Phil. Trans., 1874.
 
(453) W. K. Parker. "On the structure and development of the skull in the
Batrachia." Part II. Phil. Trans., 1876.
 
(454) W. K. Parker. "On the structure and development of the skull in the
Urodelous Amphibia." Part in. Phil. Trans., 1877.
 
(455) W. K. Parker. "On the structure and development of the skull in the
Common Snake (Tropidonotus natrix)." Phil. Trans. , 1878.
 
(456) W. K. Parker. "On the structure and development of the skull in Sharks
and Skates." Trans. Zoolog. Soc., 1878. Vol. x. pt. iv.
 
(1.17) W. K. Parker. "On the structure and development of the skull in the
Lacertilia." Pt. I. Lacerta agilis, L. viridis and Zootoca vivipara. Phil. Trans.,
1879.
 
 
 
BIBLIOGRAPHY,
 
 
 
(458) W. K. Parker. "The development of the Green Turtle." The Zoolo-v
of the Voyage of H.M.S. Challenger. Vol. I. pt. v.
 
(459) W. K. Parker. "The structure and development of the skull in the
Batrachia." 1't. in. Phil. Trans., 1880.
 
(460) W. K. Parker and G. T. Bettany. The Morphology of the Skull.
London, 1877.
 
(460*) H. Rathke. Entwick. d. Natter. Konigsberg, 1830.
 
(461) C. B. Reichert. " Ueber die Visceralbogen d. Wirbelthiere." Mailer's
Archiv, 1837.
 
(462) W. Salensky. " Beitrage z. Entwick. d. knorpeligen Gehorknochelchen."
Morphol. Jahrbuch, Vol. VI. 1880.
 
Vide also Kolliker (No. 298), especially for the human and mammalian skull;
Gotte (No. 296).
 
THE PECTORAL GIRDLE.
 
(463) Bruch. "Ueber die Entwicklung der Clavicula und die Farbe des
Blutes." Zeit.f. wiss. Zool., IV. 1853.
 
(464) A. Duges. " Recherches sur 1'osteologie et la myologie des Batraciens a
leurs differents ages." Memoires des savants etrang. Academic royale des sciences de
Finstitut de France, Vol. VI. 1835.
 
(465) C. Gegenbaur. Unterstichungen zur vergleichenden Anatomic der Wirbelthiere, i Heft. Schultergilrtel der Wirbelthiere. Brustflosse der Fische. Leipzig,
1865.
 
(466) A. Gotte. "Beitrage z. vergleich. Morphol. d. Skeletsystems d. Wirbelthiere : Brustbien u. Schultergiirtel. " Archiv f. mikr. Anat. Vol. XIV. 1877.
 
(467) C. K. Hoffmann. "Beitrage z. vergleichenden Anatomic d. Wirbelthiere." Niederldndisches Archiv f. Zool. , Vol. V. 1879.
 
(468) W. K. Parker. " A Monograph on the Structure and Development of the
Shoulder-girdle and Sternum in the Vertebrata." Ray Society, 1868.
 
(469) H. Rathke. Ueber die Entwicklung der Schildkroten. Braunschweig,
1848.
 
(470) H. Rathke. Ueber den Bau und die Entwicklung des Brustbeins der
Satirier, 1853.
 
(471) A. Sab a tier. Comparaison des ceintures et des menibres anteneurs et posterieurs d. la Serie d. Vertebrcs. Montpellier, 1880.
 
(472) Georg 'Swirski. Untersuch. lib. d. Entwick. d. Schultergiirtels u. d.
Skelets d. Brustflosse d. Hechts. Inaug. Diss. Dorpat, 1880.
 
THE PELVIC GIRDLE.
 
(473) A. Bunge. Untersuch. z. Entwick. d. Beckengilrtels d. Amphibien,
Reptilien u. Vdgel. Inaug. Diss. Dorpat, 1880.
 
(474) C. Gegenbaur. " Ueber d. Ausschluss des Schambeins von d. Pfanne
d. Hiiftgelenkes." Morph. Jahrbuch, Vol. II. 1876.
 
(475) Th. H. Huxley. "The characters of the Pelvis in Mammalia, etc."
Proc. of Roy. Soc., Vol. xxvin. 1879.
 
(476) A. S aba tier. Comparaison des ceintures et des membres anterieurs ct
postb-ieurs dans la Serie d. Vertebres. Montpellier, 1880.
 
SKELETON OF THE LIMBS.
 
(477) M. v. Davidoff. "Beitrage z. vergleich. Anat. d. hinteren Gliedmaassen
d. Fische I." Morphol. Jahrbuch, Vol. v. 1879.
 
(478) C. Gegenbaur. Untersuchungen z. vergleich. Anat. d. Wirbelthiere.
Leipzig, 18645. Erstes Heft. Carpus u. Tarsus. Zweites Heft. Brustflosse d.
Fische.
 
(479) C. Gegenbaur. "Ueb. d. Skelet d. Gliedmaassen d. Wirbelthiere im
Allgemeinen u. d. Hintergliedmaassen d. Selachier insbesondere." Jenaische Zeilschrift, Vol. V. 1870.
 
 
 
XX BIBLIOGRAPHY.
 
 
 
(480) C. Gegenbaur. " Ueb. d. Archipterygium." Jenaische Zeitschrift, Vol.
vn. 1873.
 
(481) C. Gegenbaur. "Zur Morphologic d. Gliedmaassen d. Wirbelthiere."
Morphologisches Jahrbuch, Vol. II. 1876.
 
(482) A. Gotte. Ueb. Entwick. u. Regeneration d. Gliedmaassenskelets d. Molche.
Leipzig, 1879.
 
(483) T. H. Huxley. "On Ceratodus Forsteri, with some observations on the
classification of Fishes." Proc. Zool. Soc. 1876.
 
(484) St George Mivart. "On the Fins of Elasmobranchii." Zoological
Trans., Vol. x.
 
(485) A. Rosenberg. "Ueb. d. Entwick. d. Extremitaten-Skelets bei einigen
d. Reduction ihrer Gliedmaassen charakterisirten Wirbelthiere." Zeit.f. wiss. Zool.,
Vol. xxin. 1873.
 
(486) E. Rosenberg. "Ueb. d. Entwick. d. Wirbelsaule u. d. centrale carpi
d. Menschen." Morphologisches Jahrbuch, Vol. I. 1875.
 
(487) H. Strasser. "Z. Entwick. d. Extremitatenknorpel bei Salamandern u.
Tritonen." Morphologisches Jahrbuch, Vol. V. 1879.
 
(488) G. 'S wirski. Unterstich. iib. d. Entwick. d. Schnltergiirtels u. d. Skelets d.
Brustflosse d. Hechts. Inaug. Diss. Dorpat, 1880.
 
(489) J. K. Thacker. "Median and paired fins. A contribution to the history
of the Vertebrate limbs." Trans, oftke Connecticut Acad., Vol. III. 1877.
 
(490) J. K. Thacker. "Ventral fins of Ganoids." Trans, of the Connecticut
Acad., Vol. IV. 1877.
 
PLEURAL AND PERICARDIAL CAVITIES.
 
(491) M. Cadiat. " Du developpement de la partie cephalothoracique de 1'embryon, de la formation du diaphragme, des pleures, du pericarde, du pharynx et de
1'cesophage." Journal de FAnatomie et de la Physiologic, Vol. xiv. 1878.
 
VASCULAR SYSTEM.
The Heart.
 
(492) A. C. Bernays. " Entwicklungsgeschichte d. Atrioventricularklappen."
Morphol. Jahrbuch, Vol. 11. 1876.
 
(493) E. Gasser. " Ueber d. Entstehung d. Herzens beim Hiihn." Archiv f.
mikr. Anat., Vol. xiv.
 
(494) A. Thomson. "On the development of the vascular system of the foetus
of Vertebrated Animals." Edinb. New Phil. Journal, Vol. ix. 1830 and 1831.
 
(495) M. Tonge. "Observations on the development of the semilunar valves
of the aorta and pulmonary artery of the heart of the Chick." Phil. Trans. CLIX.
1869.
 
Vide also Von Baer (291), Rathke (300), Hensen (182), Kolliker (298), Gotte (296),
and Balfour (292).
 
The Arterial System.
 
(496) H. Rathke. "Ueb. d. Entwick. d. Arterien w. bei d. Saugethiere von
d. Bogen d. Aorta ausgehen." Miiller's Archiv, 1843.
 
(41)7) PI. Rathke. " Untersuchungen iib. d. Aortenwurzeln d. Saurier."
Denkschriften d. k. Akad. Wien, Vol. xiil. 1857.
 
Vide also His (No. 232) and general works on Vertebrate Embryology.
 
The Venous System.
 
(498) J.Marshall. "On the development of the great anterior veins." Phil.
Trans., 1859.
 
 
 
BIHLIOGRAI'IIY. XXJ
 
 
 
(499) H. Rathke. " Ueb. d. Bildung d. Pfortader u. d. Lebervenen b. Sauge
thieren." Meckel 's Archiv, 1830.
 
(500) H. Rathke. "Ueb. d. Bau u. d. Entwick. d. Venensystems d. Wirbclthiere." Bericht. iib. d. natttrh. Seminar, d. Univ. Konigsberg, 1838.
 
Vide also Von Baer (No. 291), Gotte (No. 296), Kolliker (No. 298), and Rathke
(Nos. 299, 300, and 301).
 
THE SPLEEN.
 
(501) W. Miiller. "The Spleen." Strieker's Histology.
 
(502) Peremeschko. "Ueb. d. Entwick. d. Milz." Silz. d. Wien. Akad.
Wiss., Vol. LVI. 1867.
 
THE SUPRARENAL BODIES.
 
(503) M. Braun. "Bau u. Entwick. d. Nebennieren bei Reptilian." Arbeit,
a. d. zool.-zoot. Institut Wilrzburg, Vol. v. 1879.
 
(504) A. v. Brunn. "Ein Beitrag z. Kenntniss d. feinern Baues u. d. Entwick.
d. Nebennieren." Archiv f. mikr. Anat., Vol. vni. 1872.
 
(505) Fr. Leydig. Untersuch. ilb. Fische u. Reptilien. Berlin, 1853.
 
(506) Fr. Leydig. Rochen u. Haie. Leipzig, 1852.
 
Vide also F. M. Balfour (No. 292), Kolliker (No. 298), Remak (No. 302), etc.
 
THE MUSCULAR SYSTEM OF THE VERTEBRATA.
 
(507) G.M.Humphry. " Muscles in Vertebrate Animals." J our n. of Anat.
and Phys., Vol. vi. 1872.
 
(508) J. Miiller. "Vergleichende Anatomic d. Myxinoiden. Part I. Osteologie
u. Myologie." Akad. Wiss., Berlin, 1834.
 
(509) A. M. Marshall. "On the head cavities and associated nerves of
Elasmobranchs." Quart. J. of Micr. Science, Vol. XXI. 1881.
 
(510) A. Schneider. "Anat. u. Entwick. d. Muskelsystems d. Wirbelthiere."
Sitz. d. Oberhessischen Gesellschaft, 1873.
 
(511) A. Schneider. Beitrdge z. vergleich. Anat. u. Entwick. d. Wirbelthiere.
Berlin, 1879.
 
Vide also Gotte (No. 296), Kolliker (No. 298), Balfour (No. 292), Huxley, etc.
 
EXCRETORY ORGANS.
 
INVER TEBRA TA .
 
(512) H. Eisig. " Die Segmentalorgane d. Capitelliden." Mitth. a. d. zool.
Slat. z. Neapel, Vol. I. 1879.
 
(513) J. Fraipont. " Recherches s. 1'appareil excreteur des Irematc
Cestoides." Archives de Biologie, Vol. I. 1880.
 
(514) B. Hatschek. "Studien iib. Entwick. d. Annehden. Arbeit, a. d.
zool. Instil. Wien, Vol. I. 1878. .
 
(515) B. Hatschek. "Ueber Entwick. von Echmrus, etc. Arbeit, a.
 
zool. Instit. Wien, Vol. ill. 1880.
 
VERTEBRATA.
 
General.
 
(516) F. M. Balfour. "On the origin and history of the urinogenital organs of
Vertebrates." Journal of Anat. and Phys., Vol. X. 1876.
 
 
 
XXJi BIBLIOGRAPHY.
 
 
 
(517) Max. Fiirbringer 1 . "Zur vergleichenden Anat. u. Entwick. d. Excretionsorgane d. Vertebraten." Morphol. Jahrbuch, Vol. IV. 1878.
 
(518) H. Meckel. Zur Morphol. d. Harn- u. Geschlechtswerkz.d. Wirbelthiere,
etc. Halle, 1848.
 
(519) Job. Mtiller. Bildungsgeschichte d. Genitalien, etc. Diisseldorf, 1830.
 
(520) H. Ratbke. "Beobachtungen u. Betrachtungen ii. d. Entwicklung d.
Geschlechtswerkzeuge bei den Wirbelthieren." N. Schriften d. naturf. Gesell. in
Dantzig, Bd. I. 1825.
 
(521) C. Semper 1 . "Das Urogenitalsystem d. Plagiostomen u. seine Bedeutung f. d. ubrigen Wirbelthiere." Arb. a. d. zool.-zoot. Insiit. Wiirzburg, Vol. u.
 
1875
(522) W. Waldeyer 1 . Eierstock u. Ei. Leipzig, 1870.
 
ElasmobrancJdi.
 
(523) A. Schultz. "Zur Entwick. d. Selachiereies." Archiv f. mikr. Anal.,
Vol. xi. 1875.
 
Vide also Semper (No. 521) and Balfour (No. 292).
 
Cyclostomata.
 
(524) J. M uller. " Untersuchungen ii. d. Eingeweide d. Fische. " Abh. d. k.
Ak. Wiss. Berlin, 1845.
 
(525) W. Muller. "Ueber d. Persistenz d. Urniere b. Myxine glutinosa."
Jenaische Zeitschrift, Vol. VII. 1873.
 
(526) W. Muller. "Ueber d. Urogenitalsystem d. Amphioxus u. d. Cyclostomen." Jenaische Zeitschrift, Vol. ix. 1875.
 
(527) A. Schneider. Beitrdge z. vergleich. Anat. u. Entwick. d. Wirbelthiere.
Berlin, 1879.
 
(528) W. B. Scott. "Beitrage z. Entwick. d. Petromyzonten." Morphol.
Jahrbuch, Vol. vn. 1881.
 
Teleostei.
 
(529) J. Hyrtl. "Das uropoetische System d. Knochenfische." Denkschr. d.
k. k. Akad. Wiss. Wien, Vol. II. 1850.
 
(530) A. Rosenberg. Untersuchungen iib. die Enlwicklung d. Teleostierniere.
Dorpat, 1867.
 
Vide also Oellacher (No. 72).
 
Amphibia.
 
(531) F. H. Bidder. Vergleichend-anatomische u. histologisclie Untcrsiiclniii^cn
ii. die mdnnlichcn Geschlec/its- tmd Harmverkzeuge d. nackten Amphibien. Dorpat,
1846.
 
(532) C. L. Duvernoy. "Fragments s. les Organes genito-urinaires des
Reptiles," etc. Mem. Acad. Sciences. Paris. Vol. xi. 1851, pp. 17 95.
 
(533) M. Fiirbringer. Zur Entwicklung d. Amphibienniere. Heidelberg, 1877.
 
(534) F. Ley dig. Analomie d. Amphibien u. Keptilien. Berlin, 1853.
 
(535) F. Leydig. Lehrbuch d. Histologie. Hamm, 1857.
 
(536) F. Meyer. "Anat. d. Urogenitalsystems d. Selachier u. Amphibien."
Sitz. d. naturfor. Gesellsch. Leipzig, 1875.
 
(537) J. W. Spengel. "Das Urogenitalsystem d. Amphibien." Arb. a. d.
zool.- zoot. Instil. Wiirzburg. Vol. in. 1876.
 
(538) Von Wittich. "Harn- u. Geschlechtswerkzeuge d. Amphibien." Zeit.
f. wiss. Zool., Vol. iv.
 
Vide also Gotte (No. 296).
 
1 The papers of Fiirbringer, Semper and Waldeyer contain full references to the
literature of the Vertebrate excretory organs.
 
 
 
BIBLIOGRAPHY. xxiii
 
 
 
Amniota.
 
(539) F. M. Balfour and A. Sedgwick. "On the existence of ahead-kidney
in the embryo Chick," etc. Quart. J. of Micr. Science, Vol. XIX. 1878.
 
(540) Banks. On the Wolffian bodies of the foetus and their remains in the adult.
Edinburgh, 1864.
 
(541) Th. Bornhaupt. UntersucJnmgen iib. die Entwicklung d. Urogenitalsystems beim Hiihnchen. Inaug. Diss. Riga, 1867.
 
(542) Max Braun. "Das Urogenitalsystem d. einheimischen Reptilien."
Arbeiten a. d. zool.-zoot. Instit. Wiirzburg. Vol. IV. 1877.
 
(543) J. Dansky u. J. Kostenitsch. " Ueb. d. Entwick. d. Keimblatter u. d.
Wolffschen Ganges im Htihnerei." Me"m. Acad. Imp. Petersbourg, vn. Series, Vol.
xxvn. 1880.
 
(544) Th. Egli. Beitrdge zur Anat. tmd Entiuick. d. Geschlechtsorgane. Inaug.
Diss. Zurich, 1876.
 
(545) E. Gasser. Beitrdge zur Entwickhmgsgeschichte d. Allantois, der
MiUler' schen Giinge u. des Afters. Frankfurt, 1874.
 
(546) E. Gasser. " Beob. iib. d. Entstehung d. WolfFschen Ganges bei Embryonen von Hiihnern u. Gansen." Arch, fiir mikr. Anat., Vol. xiv. 1877.
 
(547) E. Gasser. "Beitrage z. Entwicklung d. Urogenitalsystems d. Htihnerembryonen." Sitz. d. Cesell. zur Beforderung d. gesam. Naturwiss. Marburg, 1879.
 
(548) C. Kupffer. " Untersuchung liber die Entwicklung des Harn- und Geschlechtssystems." Archiv fiir mikr. Anat., Vol. II. 1866.
 
(549) A. Sedgwick. "Development of the kidney in its relation to the
Wolffian body in the Chick." Quart. J. of Micros. Science, Vol. XX. 1880.
 
(550) A. Sedgwick. "On the development of the structure known as the
glomerulus of the head -kidney in the Chick." Quart. J. of Micros. Science, Vol. XX.
1880.
 
(551) A. Sedgwick. "Early development of the Wolffian duct and anterior
Wolffian tubules in the Chick ; with some remarks on the vertebrate excretory
system." Quart. J. of Micros. Science, Vol. xxi. 1881.
 
(552) M. Watson. "The homology of the sexual organs, illustrated by comparative anatomy and pathology." Journal of Anat. and Phys., Vol. XIV. 1879.
 
(553) E. H. Weber. Zusdtze z, Lehre von Bane u. d. Verrichtungen d. Geschlechtsorgane. Leipzig, 1846.
 
Vide also Remak (No. 302), Foster and Balfour (No. 295), His (No. 297),
Kolliker (No. 298).
 
GENERATIVE ORGANS.
 
(554) G. Balbiani. Lemons s. la generation des Vertebres. Paris, 1879.
 
(555) F. M. Balfour. "On the structure and development of the Vertebrate
ovary." Quart. J. of Micr. Science, Vol. XVIII.
 
(556) E. van Beneden. "De la distinction originelledutecticuleet del'ovaire,
etc." Bull. Ac. roy. belgique, Vol. xxxvn. 1874.
 
(557) N. Kleinenberg. "Ueb. d. Entstehung d. Eier b. Eudendrhim." Zeit.
f. wiss. Zool., Vol. xxxv. 1 88 r.
 
(558) H. Ludwig. "Ueb. d. Eibildung im Theirreiche. " Arbeit, a. d. zool.zoot. Instit. Wiirzburg, Vol. I. 1874.
 
(559) C. Semper. "Das Urogenitalsystem d. Plagiostomen, etc." Arbeit, a.
d. zool.-zoot. Instit. Wiirzburg, Vol. II. 1875.
 
(560) A. Weismann. "Zur Frage nach clem Ursprung d. Geschlechtszellen bei
den Hydroiden." Zool. Anzeiger, No. 55, 1880.
 
Vide also O. and R. Hertwig (No. 271), Kolliker (No. 298), etc.
 
ALIMENTARY CANAL AND ITS APPENDAGES.
 
(561) B. Afanassiew. " Ueber Bau u. Entwicklung d. Thymus d. Saugeth."
Archiv f. mikr. Anat. Bd. XIV. 1877.
 
 
 
XXIV BIBLIOGRAPHY.
 
 
 
(562) Fr. Boll. Das Princip d. Wachsthums. Berlin, 1876.
 
(563) E. Gasser. "Die Entstehung d. Cloakenoffhung hei Hiihneremhryonen."
Archiv f. Anat. u. Physiol., Anat. Abth. 1880.
 
(564) A. Gotte. Beitrage zur Entwicklungsgeschichte 'd. Darmkanah im
Hithnchcn. 1867.
 
(565) W. Miiller. " Ueber die Entwickelung der Schilddriise." ycnaische
Zeitschrift, Vol. vi. 1871.
 
(566) W. Miiller. "Die Hypobranchialrinne d. Tunicaten." Jenaischc Zeitschrift, Vol. VII. 1872.
 
(567) S. L. Schenk. "Die Bauchspeicheldriise d. Embryo." Anatomischphysiologische UntersucJnmgcn. 1872.
 
(568) E. Selenka. " Beitrag zur Entwicklungsgeschichte d. Luftsacke d.
Huhns." Zeit.f. wiss. Zool. 1866.
 
(569) L. Stieda. Untersuch. lib. d. Entivick. d. Glandula Thymus, Glandula
thyroidea, u. Glandula carotica. Leipzig, 1881.
 
(570) C. Fr. Wolff. " De formatione intestinorum." Nov. Comment. Akad.
Petrop. 1766.
 
(571) A. Wblfler. Ueb. d. Entwick. it. d. Ban d. Schilddriise. Berlin, 1880.
Vide also Kolliker (298), Qotte (296), His (232 and 297), Foster and Balfour (2!)5),
 
Balfour (292), Remak (302), Schenk (303), etc.
 
Teeth.
 
(572) T. H. Huxley. "On the enamel and dentine of teeth." Quart. J. of
Micros. Science, Vol. III. 1855.
 
(573) R. Owen. Odontography. London, 1840 1845.
 
(574) Ch. S. Tomes. Manual of dental anatomy, human and comparative.
London, 1876.
 
(575) Ch. S. Tomes. " On the development of teeth." Quart. J. of Micros.
Science, Vol. xvi. 1876.
 
(576) W. Waldeyer. " Structure and development of teeth." Strieker 's Histology. 1870.
 
Vide also Kolliker (298), Gegenbaur (294), Hertwig (306), etc.
 
 
 
 
 
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Foster M. and Sedgwick A. The Works of Francis Balfour Vol. III. A Treatise on Comparative Embryology 2 (1885) MacMillan and Co., London.

Cephalochorda | Urochorda | Elasmobranchii | Teleostei | Cyclostomata | Ganoidei | Amphibia | Aves | Reptilia | Mammalia | Comparison of the Formation of Germinal Layers and Early Stages in Vertebrate Development | Ancestral form of the Chordata | General Conclusions | Epidermis and Derivatives | The Nervous System | Organs of Vision | Auditory, Olfactory, and Lateral Line Sense Organs | Notochord, Vertebral Column, Ribs, and Sternum | The Skull | Pectoral and Pelvic Girdles and Limb Skeleton | Body Cavity, Vascular System and Glands | The Muscular System | Excretory Organs | Generative Organs and Genital Ducts | The Alimentary Canal and Appendages in Chordata
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This historic 1885 book edited by Foster and Sedgwick is the third 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.



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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Pages where the terms "Historic" (textbooks, papers, people, recommendations) appear on this site, and sections within pages where this disclaimer appears, indicate that the content and scientific understanding are specific to the time of publication. This means that while some scientific descriptions are still accurate, the terminology and interpretation of the developmental mechanisms reflect the understanding at the time of original publication and those of the preceding periods, these terms, interpretations and recommendations may not reflect our current scientific understanding.     (More? Embryology History | Historic Embryology Papers)


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Vol. III. A Treatise on Comparative Embryology 2 (1885)

Chapter XXIV. Generative Organs And Genital Ducts

GENERATIVE ORGANS.

THE structure and growth of the ovum and spermatozoon were given in the first chapter of this work, but their derivation from the germinal layers was not touched on, and it is this subject with which we are here concerned. If there are any structures whose identity throughout the Metazoa is not open to doubt these structures are the ovum and spermatozoon ; and the constancy of their relations to the germinal layers would seem to be a crucial test as to whether the latter have the morphological importance usually attributed to them.

The very fragmentary state of our knowledge of the origin of the generative cells has however prevented this test being so far very generally applied.

Porifera. In the Porifera the researches of Schulze have clearly demonstrated that both the ova and the spermatozoa take their origin from indifferent cells of the general parenchyma, which may be called mesoblastic. The primitive germinal cells of the two sexes are not distinguishable ; but a germinal cell by enlarging and becoming spherical gives rise to an ovum ; and by subdivision forms a sperm-morula, from the constituent cells of which the spermatozoa are directly developed.

Ccelenterata. The greatest confusion prevails as to the germinal layer from which the male and female products are derived in the Ccelenterata 1 .

1 E. van Beneden (No. 556) was the first to discover a different origin for the generative products of the two sexes in Hydractinia, and his observations have led to numerous subsequent researches on the subject. For a summary of the observations on the Hydroids vide Weismann (No. 560).


742 CCELENTERATA.


The following apparent modes of origin of these products have been observed.

(1) The generative products of both sexes originate in the ectoderm (epiblast) : Hydra, Cordylophora, Tubularia, all (?) free Gonophores of Hydromedusae, the Siphonophora, and probably the Ctenophora.

(2) The generative products of both sexes originate in the entoderm (hypoblast) : Plumularia and Sertularella, amongst the Hydroids, and the. whole of the Acraspeda and Actinozoa.

(3) The male cells are formed in the ectoderm, and the female in the entoderm : Gonothyraea, Campanularia, Hydractinia, Clava.

In view of the somewhat surprising results to which the researches on the origin of the genital products amongst the Ccelenterata have led, it would seem to be necessary either to hold that there is no definite homology between the germinal layers in the different forms of Ccelenterata, or to offer some satisfactory explanation of the behaviour of the genital products, which would not involve the acceptance of the first alternative.

Though it can hardly be said that such an explanation has yet been offered, some observations of Kleinenberg (No. 557) undoubtedly point to such an explanation being possible.

Kleinenberg has shewn that in Eudendrium the ova migrate freely from the ectoderm into the endoderm, and vice versa ; but he has given strong grounds for thinking that they originate in the ectoderm. He has further shewn that the migration in this type is by no means an isolated phenomenon.

Since it is usually only possible to recognise generative elements after they have advanced considerably in development, the mere position of a generative cell, when first observed, can afford, after what Kleinenberg has shewn, no absolute proof of its origin. Thus it is quite possible that there is really only one type of origin for the generative cells in the Ccelenterata.

Kleinenberg has given reasons for thinking that the migration of the ova into the entoderm may have a nutritive object. If this be so, and there are numerous facts which shew that the position of generative cells is often largely influenced by their nutritive requirements, it seems not impossible


GENERATIVE ORGANS. 743

that the endodermal position of the generative organs in the Actinozoa and acraspedote Medusre may have arisen by a continuously earlier migration of the generative cells from the ectoderm into the endoderm ; and that the migration may now take place at so early a period of the development, that we should be justified in formally holding the generative products to be endodermal in origin.

\Ve might perhaps, on this view, formulate the origin of the generative products in the Ccelenterata in the following way :

Both ova and spermatozoa primitively originated in the ectoderm, but in order to secure a more complete nutrition the cells which give rise to them exhibit in certain groups a tendency to migrate into the endoderm. This migration, which may concern the generative cells of one or of both the sexes, takes place in some cases after the generative cells have become recognisable as such, and very probably in other cases at so early a period that it is impossible to distinguish the generative cells from indifferent embryonic cells.

Very little is known with reference to the origin of the generative cells in the triploblastic Invertebrata.

Chaetopoda and Gephyrea. In the Chaetopoda and Gephyrea, the germinal cells are always developed in the adult from the epithelial lining of the body cavity ; so that their origin from the mesoblast seems fairly established.

If we are justified in holding the body cavity of these forms to be a derivative of the primitive archenteron (vide pp. 356 and 357) the generative cells may fairly be held to originate from a layer which corresponds to the endoderm of the Ccelenterata 1 .

Chaetognatha. In Sagitta the history of the generative cells, which was first worked out by Kowalevsky and Biitschli, has been recently treated with great detail by O. Hertwig 2 .

The generative cells appear during the gastrula stage, as two large cells with conspicuous nuclei, which are placed in the hypoblast lining the archenteron, at the pole opposite the blastopore. These cells soon divide, and at the same time pass out of the hypoblast, and enter the archenteric cavity (fig. 408 - A, ge). The division into four cells, which is not satisfactorily represented ifl my diagram, takes place in such a way that two

1 The Hertwigs (No. 271) state that in their opinion the generative cells arise from the lining of the body cavity in all the forms whose body cavity is a product of the archenteron. We do not know anything of the embryonic development of the generative organs in the Echinodermata, but the adult position of the generative organs in this group is very unfavourable to the Hertwigs' view.

2 O. Hertwig, Die Chcetognathen. Jena, 1880


744


CH^ETOGNATHA.


cells are placed nearer the median line, and two externally. The two inner cells form the eventual testes, and the outer the



FIG. 408. THREK STAGES IN THE DEVELOPMENT OF SAGITTA. (A and C after

Biitschli, and B after Kowalevsky.) The three embryos are represented in the same positions.

A. Represents the gastrula stage.

B. Represents a succeeding stage, in which the primitive archenteron is commencing to be divided into three.

C. Represents a later stage, in which the mouth involution (in) has become continuous with the alimentary tract, and the blastopore is closed.

///. mouth ; al. alimentary canal ; ac. archenteron ; bl.p. blastopore ; pv. perivisceral cavity ; sp, splanchnic mesoblast ; so. somatic mesoblast ; ge. generative organs.

ovaries, one half of each primitive cell thus forming an ovary, and the other a testis.



FIG. 409. Two VIEWS OF A LATE EMBRYO OF SAGITTA. A, from the dorsal

surface. B, from the side. (After Biitschli.)

m. mouth ; al. alimentary canal ; v.g. ventral ganglion (thickening of epiblast) ; <.'/. epiblast ; c.pv. cephalic section of body cavity ; so. somatopleure ; sp. splanchnopleure ; ge. generative organs.


GENERATIVE ORGANS.


745


When the archenteric cavity is divided into a median alimentary tract, and two lateral sections forming the body cavity, the generative organs are placed in the common vestibule into which both the body cavity and alimentary cavity at first open (fig. 408).

The generative organs long retain their character as simple cells. Eventually (fig. 409) the two ovaries travel forwards, and apply themselves to the body walls, while the two testes also become separated by a backward prolongation of the median alimentary tract.

On the formation of the transverse septum dividing the tail from the body, the ovarian cells lie immediately in front of this septum, and the testicular cells in the region behind it.

Polyzoa. In Pedicellina amongst the entoproctous Polyzoa Hatschek finds that the generative organs originate from a pair of specially large mesoblast cells, situated in the space between the stomach and the floor of the vestibule. The two cells undergo changes, which have an obvious resemblance to those of the generative cells of the Chsetognatha. They become surrounded by an investment of mesoblast cells, and divide so as to form two masses. Each of these masses at a later period separates into an anterior and a posterior part. The former becomes the ovary, the latter the testis.

Nematoda. In the Nematoda the generative organs are derived from the division of a single cell which would appear to be mesoblastic 1 .

Insecta. The generative cells have been observed at a very early embryonic stage in several insect forms (Vol. II. p. 404), but the observations so far recorded with reference to them do not enable us to determine with certainty from which of the germinal layers they are derived.

Crustacea. In Moina, one of the Cladocera, Grobben 2 has shewn that the generative organs are derived from a single cell, which becomes differentiated during the segmentation. This cell, which is in close contiguity with the cells from which both the mesoblast and hypoblast originate, subsequently divides ;

1 Fide Vol. n. p. 374; also Gotte, Zool. Anzeiger, No. 80, p. 189.

2 C. Grobben. "Die Entwick. d. Moina rectirostris." Arbeit, a. d. zool. Instil. Wien. Vol. II. 1879.


746


CHORDATA.


sp.c


but at the gastrula stage, and after the mesoblast has become formed, the cells it gives rise to are enclosed in the epiblast, and do not migrate inwards till a later stage. The products of the division of the generative cell subsequently divide into two masses. It is not possible to assign the generative cell of Moina to a definite germinal layer. Grobben, however, thinks that it originates from the division of a cell, the remainder of which gives rise to the hypoblast.

Chordata. In the Vertebrata, the primitive generative cells (often known as primitive ova) are early distinguishable, being imbedded amongst the cells of two linear streaks of peritoneal epithelium, placed on the dorsal side of the body cavity, one on each side of the mesentery (figs. 405 C and 4io,/0). They appear to be derived from the epithelial cells amongst which they lie ; and are characterized by containing a large granular nucleus, surrounded by a considerable body of protoplasm. The peritoneal epithelium in which they are placed is known as the germinal epithelium.

It is at first impossible to distinguish the germinal cells which will become ova from those which will become spermatozoa.

The former however remain within the peritoneal epithelium (fig. 41 1), and become converted into ova in a manner more particularly described in Vol. II. pp. 54 59.

The history of the primitive germinal cells in the male has not been so adequately worked out as in the female.

The fullest history of them is that given by Semper (No. 559) for the Elasmobranchii, the general accuracy of which I can fully support ;



FIG. 410. SECTION THROUGH THE TRUNK OF A SCYLLIUM EMBRYO SLIGHTLY YOUNGER

THAN 28 F.

sp.c. spinal cord ; W. white matter of spinal cord ; pr. posterior nerve-roots ; ch. notochord ; x. sub-notochordal rod ; ao. aorta ; mp. muscle-plate ; mp'. inner layer of- muscle-plate already converted into muscles ; Vr. rudiment of vertebral body ; st. segmental tube; sd. segmental duct; sp.v. spiral valve ; v. subintestinal vein ; i>.o. primitive generative cells.


GENERATIVE ORGANS.


747


though with reference to certain stages in the history further researches are still required 1 .

In Elasmobranchii the male germinal cells, instead of remaining in the germinal epithelium, migrate into the adjacent stroma, accompanied I believe by some of the indifferent epithelial cells. Here they increase in number, and give rise to masses of variable form, composed partly of true germinal cells, and partly of smaller cells with deeply staining nuclei, which are, I believe, derived from the germinal epithelium.



FIG. 411. TRANSVERSE SECTION THROUGH THE OVARY OF A YOUNG EMBRYO OK SCYLLIUM CANICULA, TO SHEW THE PRIMITIVE GERMINAL CELLS (po) LYING IN THE GERMINAL EPITHELIUM ON THE OUTER SIDE OF THE OVARIAN RIDGE.

These masses next break up into ampullae, mainly formed of germinal cells, and each provided with a central lumen ; and these ampullae attach themselves to tubes derived from the smaller cells, which are in their turn continuous with the testicular network. The spermatozoa are developed from the cells forming the walls of the primitive ampulla;; but the process of their formation does not concern us in this chapter.

In the Reptilia Braun has traced the passage of the primitive germinal cells into the testicular tubes, and I am able to confirm his observations on this point : he has not however traced their further history.

1 Balbiani (No. 554) has also recently dealt with this subject, but I cannot bring my own observations into accord with his as to the structure of the Elasmobranch testis.


MODE OF EXIT OF GENITAL PRODUCTS.


In Mammalia the evidence of the origin of the spermatospores from the germinal epithelium is not quite complete, but there can be but little doubt of its occurrence 1 .

In Amphioxus Langerhans has shewn that the ova and spermatozoa are derived from similar germinal cells, which may be compared to the germinal epithelium of the Vertebrata. These cells are however segmentally arranged as separate masses (vide Vol. II. p. 54).

BIBLIOGRAPHY.

(554) G. Balbiani. Lemons s. la generation des Vcrlebrcs. Paris, 1879.

(555) F. M. Balfour. "On the structure and development of the Vertebrate ovary." Quart, J. of Micr. Science, Vol. xvm.

(556) E. van Beneden. "De la distinction originelle dutecticule et clel'ovaire, etc." Bull. Ac. roy. belgique, Vol. xxxvil. 1874.

(557) N. Kleinenberg. "Ueb. d. Entstehung d. Eier b. Eudendrium." Zcit. f. -wiss. Zool., Vol. xxxv. 1881.

(558) H. Ludwig. "Ueb. d. Eibildung im Theirreiche." Arbeit, a. d. zool.zoot. Inslit. Wilrzburg, Vol. I. 1874.

(559) C. Semper. "Das Urogenilalsystem d. Plagiostomen, etc." Arbeit, a. d. zooL-zoot. Ins tit. Witrzbiirg, Vol. II. 1875.

(560) A. Weismann. "Zur Frage nach dem Ursprung d. Geschlechtszellen bei den Hydroiden." Zool. Anzeiger, No. 55, 1880.

Fitffcalso O. and R. Hertwig (No. 271), Kolliker (No. 298), etc.

GENITAL DUCTS.

The development and evolution of the generative ducts is as yet very incompletely worked out, but even in the light of our present knowledge a comparative review of this subject brings to light features of considerable interest, and displays a fruitful field for future research.

In the Ccelenterata there are no generative ducts.

In the Hydromedusae and Siphonophora the generative products are liberated by being dehisced directly into the surrounding medium ; while in the Acraspeda, the Actinozoa and the Ctenophora, they are dehisced into parts of the gastrovascular system, and carried to the exterior through the mouth.

The arrangement in the latter forms indicates the origin of

1 An entirely different view of the origin of the sperm cells has been adopted by Balbiani, for which the reader is referred to his Memoir (No. 554).


GENITAL DUCTS.


749


the methods of transportation of the genital products to the exterior in many of the higher types.

It has been already pointed out that the body cavity in a very large number of forms is probably derived from parts of a gastrovascular system like that of the Actinozoa.

When the part of the gastrovascular system into which the generative products were dehisced became, on giving rise to the body cavity, shut off from the exterior, it would be essential that some mode of transportation outwards of the generative products should be constituted.

In some instances simple pores (probably already existing at the time of the establishment of a closed body cavity) become the generative ducts. Such seems probably to have been the case in the Chaetognatha (Sagitta) and in the primitive Chordata.

In the latter forms the generative products are sometimes dehisced into the peritoneal cavity, and thence transported by the abdominal pores to the exterior (Cyclostomata and some Teleostei, vide p. 626). In Amphioxus they pass by dehiscence into the atrial cavity, and thence through the gill slits and by the mouth, or by the abdominal pore (?) to the exterior. The arrangement in Amphioxus and the Teleostei is probably secondary, as possibly also is that in the Cyclostomata ; so that the primitive mode of exit of the generative products in the Chordata is still uncertain. It is highly improbable that the generative ducts of the Tunicata are primitive structures.

A better established and more frequent mode of exit of the generative products when dehisced into the body cavity is by means of the excretory organs. The generative products pass from the body cavity into the open peritoneal funnels of such organs, and thence through their ducts to the exterior. This mode of exit of the generative products is characteristic of the Chaetopoda, the Gephyrea, the Brachiopoda and the Vertebrata, and probably also of the Mollusca. It is moreover quite possible that it occurs in the Polyzoa, some of the Arthropoda, the Platyelminthes and some other types.

The simple segmental excretory organs of the Polychaeta, the Gephyrea and the Brachiopoda serve as generative canals, and in many instances they exhibit no modification, or but a very slight one, in connection with their secondary generative


750 DERIVATION FROM EXCRETORY ORGANS.

function ; while in other instances, e.g. Bonellia, such modification is very considerable.

The generative ducts of the Oligochaeta are probably derived from excretory organs. In the Terricola ordinary excretory organs are present in the generative segments in addition to the generative ducts, while in the Limicola generative ducts alone are present in the adult, but before their development excretory organs of the usual type are found, which undergo atrophy on the appearance of the generative ducts (Vedjovsky).

From the analogy of the splitting of the segmental duct of the Vertebrata into the Miillerian and Wolffian ducts, as a result of a combined generative and excretory function (vide p. 728), it seems probable that in the generative segments of the Oligochasta the excretory organs had at first both an excretory and a generative function, and that, as a secondary result of this double function, each of them has become split into two parts, a generative and an excretory. The generative part has undergone in all forms great modifications. The excretory parts remain unmodified in the Earthworms (Terricola), but completely abort on the development of the generative ducts in the Limicola. An explanation may probably be given of the peculiar arrangements of the generative ducts in Saccocirrus amongst the Polychaeta (vide Marion and Bobretzky), analogous to that just offered for the Oligochaeta.

The very interesting modifications produced in the excretory organs of the Vertebrata by their serving as generative ducts were fully described in the last chapter ; and with reference to this part of our subject it is only necessary to call attention to the case of Lepidosteus and the Teleostei.

In Lepidosteus the Mullerian duct appears to have become attached to the generative organs, so that the generative products, instead of falling directly into the body cavity and thence entering the open end of a peritoneal funnel of the excretory organs, pass directly into the Mullerian duct without entering the body cavity. In most Teleostei the modification is more complete, in that the generative ducts in the adult have no obvious connection with the excretory organs.

The transportation of the male products to the exterior in all the higher Vertebrata, without passing into the body cavity, is in principle similar to the arrangement in Lepidosteus.

The above instances of the peritoneal funnels of an excretory organ becoming continuous with the generative glands, render it highly probable that there may be similar instances amongst the In vertebrata.


GENITAL DUCTS.


751


As has been already pointed out by Gegenbaur there are many features in the structure of the genital ducts in the more primitive Mollusca, which point to their having been derived from the excretory organs. In several Lamellibranchiata 1 (Spondylus, Lima, Pecten) the generative ducts open into the excretory organs (organ of Bojanus), so that the generative products have to pass through the excretory organ on their way to the exterior. In other Lamellibranchiata the genital and excretory organs open on a common papilla, and in the remaining types they are placed close together.

In the Cephalopoda again the peculiar relations of the generative organs to their ducts point to the latter having primitively had a different, probably an excretory, function. The glands are not continuous with the ducts, but are placed in special capsules from which the ducts proceed. The genital products are dehisced into these capsules and thence pass into the ducts.

In the Gasteropoda the genital gland is directly continuous with its duct, and the latter, especially in the Pulmonata and Opisthobranchiata, assumes such a complicated form that its origin from the excretory organ would hardly have been suspected. The fact however that its opening is placed near that of the excretory organ points to its being homologous with the generative ducts of the more primitive types.

In the Discophora, where the generative ducts are continuous with the glands, the structure both of the generative glands and ducts points to the latter having originated from excretory organs.

It seems, as already mentioned, very possible that there are other types in which the generative ducts are derived from the excretory organs. In the Arthropoda for instance the generative ducts, where provided with anteriorly placed openings, as in the Crustacea, Arachnida and the Chilognathous Myriapoda, the Pcecilopoda, etc., may possibly be of this nature, but the data for deciding this point are so scanty that it is not at present possible to do more than frame conjectures.

The ontogeny of the generative ducts of the Nematoda and

1 For a summary of the facts on this subject vide Bronn, Klassen u. Ordnungen d. Thierreichs, Vol. in. p. 404.


752 DERIVATION FROM EXCRETORY ORGANS.

the Insecta appears to point to their having originated independently of the excretory organs.

In the Nematoda the generative organs of both sexes originate from a single cell (Schneider, Vol. I. No. 390).

This cell elongates and its nuclei multiply. After assuming a somewhat columnar form, it divides into (i) a superficial investing layer, and (2) an axial portion.

In the female the superficial layer is only developed distinctly in the median part of the column. In the course of the further development the two ends of the column become the blind ends of the ovary, and the axial tissue they contain forms the germinal tissue of nucleated protoplasm. The superficial layer gives rise to the epithelium of the uterus and oviduct. The germinal tissue, which is originally continuous, is interrupted in the middle part (where the superficial layer gives rise to the uterus and oviduct), and is confined to the two blind extremities of the tube.

In the male the superficial layer, which gives rise tc the epithelium of the vas deferens, is only formed at the hinder ond of the original column. In other respects the development takes place as in the female.

In the Insecta again the evidence, though somewhat conflicting, indicates that the generative ducts arise very much as in Nematodes, from the same primitive mass as the generative organs. In both of these types it would seem probable that the generative organs were primitively placed in the body cavity, and attached to the epidermis, through a pore in which their products passed out ; and that, acquiring a tubular form, the peripheral part of the gland gave rise to a duct, the remainder constituting the true generative gland. It is quite possible that the generative ducts of such forms as the Platyelminthes may have had a similar origin to those in Insecta and Nematoda, but from the analogy of the Mollusca there is nearly as much to be said for regarding them as modified excretory organs.

In the Echinodermata nothing is unfortunately known as to the ontogeny of the generative organs and ducts. The structure of these organs in the adult would however seem to indicate that the most primitive type of echinoderm generative organ consists of a blind sack, projecting into the body cavity, and opening by


GENITAL DUCTS. 753


a pore to the exterior. The sack is lined by an epithelium, continuous with the epidermis, the cells of which give rise to the ova or spermatozoa. The duct of these organs is obviously hardly differentiated from the gland ; and the whole structure might easily be derived from the type of generative organ characteristic of the Hydromedusae, where the generative cells are developed from special areas of the ectoderm, and, when ripe, pass directly into the surrounding medium.

If this suggestion is correct we may suppose that the generative ducts of the Echinodermata have a different origin to those of the majority of 1 the remaining triploblastica.

Their ducts have been evolved in forms in which the generative products continued to be liberated directly to the exterior, as in the Hydromedusae ; while those of other types have been evolved in forms in which the generative products were first transported, as in the Actinozoa, into the gastrovascular canals 2 .

1 It would be interesting to have further information about Balanoglossus.

2 These views fit in very well with those already put forward in Chapter xm. on the affinities of the Echinodermata.

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