The Works of Francis Balfour 3-23: Difference between revisions

From Embryology
mNo edit summary
 
Line 3,231: Line 3,231:


Vide also Remak (No. 302), Foster and Balfour (No. 295), His (No. 297),  
Vide also Remak (No. 302), Foster and Balfour (No. 295), His (No. 297),  
Kolliker (No. 298).  
Kolliker (No. 298).
 
 
 
==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.
 
 
 
B. III.
 
 
 
48
 
 
 
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.
 
(1) A. Kowalevsky. " Entwicklungsgeschichte des Amphioxus lanceolatus."
Mem. Acad. Imper. des Sciences de St Pttersbourg, Series vn. Tom. XI. 1867.
 
(2) A. Kowalevsky. "Weitere Studien iiber die Entwicklungsgeschichte des
Amphioxus lanceolatus." Archiv f. mikr. Anat., Vol. xui. 1877.
 
(3) Leuckart u. Pagenstecher. " Untersuchungen tiber niedere Seethiere."
Mutter's Archiv, 1858.
 
(4) Max Schultze. " Beobachtung junger Exemplare von Amphioxus." Zeit.
f. wiss. Zool., Bd. in. 1851.
 
(5) A. M. Marshall. "On the mode of Ovi position of Amphioxus." your,
of Anat. and Phys., Vol. x. 1876.
 
UROCHORDA.
 
(6) P. J. van Beneden. " Recherches s. 1'Embryogenie, 1'Anat. et la Physiol.
des Ascidies simples." Mem. Acad. Roy. de Belgique, Tom. xx.
 
(7) W. K. Brooks. "On the development of Salpa." Bull, of the Museum of
Comp. Anat. at Harvard College, Cambridge, Mass.
 
(8) H. Fol. Eludes surles Appendiculaires du detroit de Mcssine . Geneve et
Bale, 1872.
 
(9) Ganin. "Neue Thatsachen a. d. Entwicklungsgeschichte d. Ascidien."
Zeit.f. wiss. Zool., Vol. XX. 1870.
 
(10) C. Gegenbaur. " Ueber den Entwicklungscyclus von Doliolum nebst
Bemerkungen iiber die Larven dieser Thiere." Zeit.f. wiss. Zool., Bd. vu. 1856.
 
(11) A. Giard. "Etudes critiques des travaux d'embryogenie relatifs a la
parente des Vertebres et des Tuniciers." Archiv Zool. experiment., Vol. I. 1872.
 
(12) A. Giard. " Recherches sur les Synascidies. " Archiv Zool. exper., Vol. I.
1872.
 
(13) O. Hertwig. "Untersuchungen lib. d. Bau u. d. Entwicklung des Cellulose-Mantels d. Tunicaten." Jenaische Zeitschrift, Bd. vn. 1873.
 
(14) Th. H. Huxley. " Remarks upon Appendicularia and Doliolum. " Phil.
Trans., 1851.
 
(15) Th. H.Huxley. " Observations on the anatomy and physiology of Salpa
and Pyrosoma." Phil. Trans., 1851.
 
(16) Th. H. Huxley. "Anatomy and development of Pyrosoma." Linnean
Trans., 1860, Vol. XXIII.
 
(17) Keferstein u. Ehlers. Zoologische Beitrage, 1861. Doliolum.
 
(18) A. Kowalevsky. "Entwicklungsgeschichte d. einfachen Ascidien." Mem.
Acad. Pctersbourg, VII. serie, T. x. 1866.
 
(19) A. Kowalevsky. "Beitrag z. Entwick. d. Tunicaten." Nachrichtcn d.
konigl. Gesell.zu Gottingen. 1868.
 
(20) A. Kowalevsky. "Weitere Studien iib. d. Entwicklung d. einfachen Ascidien." Archiv f. mikr. Anat., Vol. vn. 1871.
 
(21) A. Kowalevsky. "Ueber Knospung d. Ascidien." Archiv f. mikr. Anat.,
Vol. X. 1874.
 
(22) A. Kowalevsky. "Ueber die Entwicklungsgeschichte d. Pyrosoma."
Archiv f. mikr. Anat., Vol. xi. 1875.
 
(23) A. Krohn. "Ueber die Gattung Doliolum u. ihre Arten." Archiv f.
Natnrgeschichte, Bd. xvm. 1852.
 
B. Hi. a
 
 
 
BIBLIOGRAPHY.
 
 
 
(24) A. Krohn. "Ueber die Entwicklung d. Ascidien." Mailer's Archiv,
1852.
 
(25) A. Krohn. "Ueber die Fortpfianzungsverhaltnisse d. Botrylliden. " Archiv
f. Naturgeschichte, Vol. xxxv. 1869.
 
(26) A. Krohn. "Ueber die fruheste Bildung d. Botryllenstocke." Archiv f.
Naturgeschichte, Vol. xxxv. 1869.
 
(27) C. Kupffer. " Die Stammverwandschaft zwischen Ascidien u. Wirbelthieren." Archiv f, mikr. Anat., Vol. vi. 1870.
 
(28) C. Kupffer. "Zur Entwicklung d. einfachen Ascidien." Archiv f. mikr.
Anat., Vol. vm. 187-2.
 
(29) H. Lacaze Duthiers. "Recherches sur 1'organisation et 1'Embryogenie
des Ascidies (Molgula tubulosa)." Comptes rendus, May 30, 1870, p. 1154.
 
(30) H. Lacaze Duthiers. "Les Ascidies simples des Cotes de France" (Development of Molgula). Archiv Zool. exper., Vol. ill. 1874.
 
(31) R. Leuckart. "Salpa u. Verwandte." Zoologischc Untcrsuchungen,
Heft u.
 
(32) E. Metschnikoff. " Observations sur le developpement de quelques animaux (Botryllus and Simple Ascidians)." Still, d. fAcad. Petersbottrg, Vol. xm.
1869.
 
(33) H. Milne-Edwards. "Observations s. 1. Ascidies composees des cotes de
la Manche." Memoir es d. V Instittit, T. xvm. 1842.
 
(34) W. Salensky. "Ueber d.embryonaleEntwicklungsgeschichtederSalpen."
Zeit.f. wiss. Zool., B. xxvn. 1877.
 
(35) W. Salensky. "Ueber die Knospung d. Salpen." Morphol. Jahrbuch,
Bd. in. 1877.
 
(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
d. Ascidien." Arbeit, a. d. zool.-zoot. Instit. Wiirzburg, Vol. ri. 1875.
 
(38) Fr. Todaro. Sopra lo sviluppo e F anatomia delle Salpc. Roma, 1875.
 
(39) Fr. Todaro. "Sui primi fenomeni dello sviluppo delle Salpe." Realc
Accadcmia dci Lincei, Vol. iv. 1880.
 
 
 
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
Fishes." London, 1878. Reprinted from the Journal of Anat. and Fhysiol. for 1876,
1877, and 1878.
 
(42) Z. Gerbe. " Recherches sur la segmentation de la cicatrule et la formation
des prodnits adventifs de Pceuf des Plagiostomes et particulierement des Rates." Vide
also Journal de FAnatomie et de la Physiologic, 1872.
 
(43) W. His. " Ueb. d. Bildung v. Haifischenembryonen." Zeit. fur Anat. u.
Entwick., Vol. 11. 1877.
 
(44) A. Kowalevsky. "Development of Acanthias vulgaris and Mustelus
Irevis. " (Russian.) Transactions of the Kiew Society of Naturalists, Vol. I. 1870.
 
(45) R. Leuckart. "Ueber die allmahlige Bildung d. Korpergestalt bei d.
Rochen." Zeit. f. wiss. Zool., Bd. II., p. 258.
 
(46) Fr. Ley dig. Rochen u. Hate. Leipzig, 1852.
 
(47) A. W. Malm. " Bidrag till kannedom om utvecklingen af Rajae." Kongl.
vetenskaps akademiens fo'rhandlingar. Stockholm, 1876.
 
(48) Joh. M tiller. Clatter Haie des Aristoteles und iiber die Verschiedenheitcn
unler den Haifachen und Rochen in der Entivicklung des Eies. Berlin, 1840.
 
(49) S. L. Schenk. " Die Eier von Raja quadrimaculata innerhalb der Eileiter."
Sitz. der k. Akad. Wien, Vol. LXXIII. 1873.
 
(50) Alex. Schultz. " Zur Entwicklungsgeschichte des Selachiereies. " Archiv
fiir micro. Anat., Vol. XI. 1875.
 
(51) Alex. Schultz. " Beitrag zur Entwicklungsgeschichte d. Knorpelfische. "
Archiv fiir micro. Anat., Vol. xni. 1877.
 
 
 
BIBLIOGRAPHY.
 
 
 
Ill
 
 
 
(52) C. Semper. "Die Stammesverwandschaft d. Wirbelthiere u. Wirlwllosen. Arbeit, a. d. zool.-zoot. Instit. Wiirzburg, Vol. II. 1875.
 
(53) C. Semper. " Das Urogenitalsystem d. Plagiostomen, etc." Arbeit, a. d.
zool.-zoot. Instit. Wiirzburg, Vol. n. 1875.
 
(54) Wyman. " Observations on the Development of Raja batis." Memoirs of
the American Academy of Arts and Sciences, Vol. ix. 1864.
 
 
 
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,
Vol. xin. Presented Oct. n, 1877.
 
(56) Al. Agassiz. "II. Development of the Flounders." Proceedings of the
American Acad. of Arts arid Sciences, Vol. xiv. Presented June, 1878.
 
(57) K. E. v. Baer. Untersuchungen ilber die Entwicklungsgeschichte der Fische.
Leipzig, 1835.
 
(58) Ch. van Bambeke. "Premiers effets de la fecondation sur les cufs de
Poissons: sur 1'origine et la signification du feuillet muqueux on glandulaire chez les
Poissons Osseux." Comptes Rendus des Seances de f Academic des Sciences, Tome
 
1872.
 
Ch. van Bambeke. " Recherches sur 1'Embryologie des Poissons
Mem. couronnes et Mem. de savants etrangers de rAcademie roy. Bclgiqne,
 
 
 
LXXIV.
 
(59)
 
Osseux. '
Vol. XL.
 
(60)
 
 
 
E. v. Beneden. "A contribution to the history of the Embryonic development of the Teleosteans." Quart. J. of Micr. Sci., Vol. xvm. 1878.
 
(61) E. Calberla. " Zur Entwicklung des Medullarrohres u. d. Chorda
dorsalis d. Teleostier u. d. Petromyzonten." Morphologisches Jahrbuch, Vol. III.
1877.
 
(62) A. Gotte. "Beitrage zur Entwicklungsgeschichte der Wirbelthiere."
Archiv f. mikr. Anat., Vol. IX. 1873.
 
(63) A. Gotte. " Ueber d. Entwicklung d. Central-Nervensystems der Teleostier." Archiv f. mikr. Anat., Vol. xv. 1878.
 
(64) A. Gotte. " Entwick. d. Teleostierkeime." Zoologischer Anzeiger, No. 3.
1878.
 
(65) W. His. " Untersuchungen Uber die Entwicklung von Knochenfischen, etc."
Zeit.f. Anat. it. Entwicklungsgeschichte, Vol. I. 1876.
 
(66) W. His. "Untersuchungen Uber die Bildung des Knochenfischembryo
(Salmen)." Archiv f. Anat. u. Physiol., 1878.
 
(67) E. Klein. "Observations on the early Development of the Common
'Trout." Quart. J. of Micr. Science, Vol. XVI. 1876.
 
~^* (68) C. Kupffer. " Beobachtungen Uber die Entwicklung der Knochenfische."
Archiv f. mikr. Anat., Bd. iv. 1868.
 
(69) C. Kupffer. Ueber Laichen u. Entwicklung des Ostsee-Herings. Berlin,
1878.
 
(70) M. Lereboullet. "Recherches sur le developpement du brochet de la
perche et de 1'ecrevisse." Annales des Sciences Nat., Vol. I., Series iv. 1854.
 
(71) M. Lereboullet. " Recherches d'Embryologie comparee sur le developpement de la Truite." An. Sci. Nat., quatrieme serie, Vol. XVI. 1861.
 
(72) T. Oellacher. " Beitrage zur Entwicklungsgeschichte der Knochenfische
nach Beobachtungen am Bachforellenei." Zeit. f. wiss. Zool., Vol. xxn., 1872, and'
Vol. xxni., 1873.
 
(72*) H. Rathke. Abh. z. Bildung u. Entwick. d. Menschen u. Thiere. Leipzig,
1832-3. Part n. Blennius.
 
(73) Reineck. " Ueber die Schichtung des Forellenkeims." Archiv f. mikr.
Anat., Bd. V. 1869.
 
(74) S. Strieker. "Untersuchungen Uber die Entwicklung der Bachforelle."
Sitzungsberichte der Wiener k. Akad. d. Wiss., 1865. Vol. LI. Abth. 2.
 
(75) Carl Vogt. " Embryologie des Salmones." Histoire Naturelle des Poissons
de F Europe Centrale. L. Agassiz. 1842.
 
(76) C.Weil. " Beitrage zur Kenntniss der Knochenfische." Silzungsbcr. doWiener kais. Akad. der Wiss., Bd. i.xvi. 1872.
 
a 2
 
 
 
BIBLIOGRAPHY.
 
 
 
CYCLOSTOMATA.
 
(77) E. Calberla. " Der Befruchtungsvorgang beim Petromyzon Planeri."
Zeit.f. iviss. Zool., Vol. xxx. 1877.
 
(78) E. Calberla. "Ueb. d. Entwicklung d. Medullarrohres u. d. Chorda
clorsalis d. Teleostier u. d. Petromyzonten." Morpholog. Jahrbuch, Vol. in. 1877.
 
(79) C. Kupffer u. B. Benecke. Der Vorgang d. Befruchtimg am Ei d.
Neunaugen. Konigsberg, 1878.
 
(80) Aug. Muller. " Ueber die Entwicklung d. Neunaugen." Miiller s
Archiv, 1856.
 
(81) Aug. Muller. Beobachtungen iib. d. Befruchtungserscheinungen im Ei d.
Neunaugen. Konigsberg, 1864.
 
(82) W. Muller. "Das Urogenitalsystem d. Amphioxus u. d. Cyclostomen. '
Jcnaische Zeitschrift, Vol. IX. 1875.
 
(83) Ph. Owsjannikoff. "Die Entwick. von d. Flussneunaugen. " ^ Vorlauf.
Mittheilung. Melanges Biologiqttcs tires du Bulletin de VAcad. Imp. St Pttersbourg,
Vol. vn. 1870.
 
(84) Ph. Owsjannikoff. On the development of Petromyzon fiuviatihs
(Russian).
 
(85) Anton Schneider. Beitrdge z. vergleich. Anat. a. Entwick. d. Wirbelthiere. Quarto. Berlin, 1879.
 
(86) M. S. Schultze. "Die Entwickl. v. Petromyzon Planeri." Gekronte
Preisschrift. Haarlem, 1856.
 
(87) W. B. Scott. " Vorlaufige Mittheilung iib. d. Entwicklungsgeschichte d.
Petromyzonten." Zoologischer Anzeiger, Nos. 63 and 64. ill. Jahrg. 1880.
 
GANOIDEI.
A cipenseridce.
 
(88) Knock. "Die Beschr. d. Reise z. Wolga Behufs d. Sterlettbefruchtung. "
Bull. Soc. Nat. Moscow, 1871.
 
(89) A. Kowalevsky, Ph. Owsjannikoff, and N. Wagner. "Die Entwick.
d. Store." Vorlauf. Mittheilung. Melanges Biologizes tires du Bulletin d. VAcad.
Imp. St Petersbowg, Vol. VII. 1870.
 
(90) W. Salensky. "Development of the Sterlet (Acipenser ruthenus)." 2 Parts.
Proceedings of the Society of Naturalists in the imperial University of Kasan. 1878 and 9
(Russian). Part I., abstracted in Hoffmann and Schwalbe's Jahresbcricht for 1878.
 
(91) W. Salensky. " Zur Embryologie d. Ganoiden (Acipenser)." Zoologischer Anzeiger, Vol. I., Nos. n, 12, 13.
 
Lepidosteidce.
 
(92) Al. Agassiz. "The development of Lepidosteus." Proc. Amer. Acad. of
Arts and Sciences, Vol. xm. 1878.
 
AMPHIBIA.
 
(93) Ch. van Bambeke. " Recherches sur le developpement du Pelobate
brun." Mc/noires coitronncs, etc. de I 1 Acad. roy. de Belgique, 1868.
 
(94) Ch. van Bambeke. "Recherches sur 1'embryologie des Batraciens."
/!iill,-tin dc V Acad. roy. de Belgique, 1875.
 
(95) Ch. van Bambeke. " Nouvelles recherches sur 1'embryologie des Batraciens." Archives de Biologic, Vol. I. 1880.
 
' (9G) K. E. von Baer. " Die Metamorphose des Eies der Batrachier." Miiller's
Archiv, 1834.
 
(97) B. Benecke. "Ueber die Entwicklung des Erdsalamanders." Zoolo. isch er An zeiger, 1880.
 
 
 
BIBLIOGRAPHY,
 
 
 
(98) S. F. Clarke. "Development of Amblystoma punctatuin," 1'art I. I
lernal. Studies from the Biological Laboratory of the Johns Hopkins University,
No. II. 1880.
 
(99) H. Cramer. "Bemerkungen iib. d. Zellenleben in d. Entwick. d.
cheies." Mliller's Archiv, 1848.
 
(100) A. Ecker. Icones Physiolog. 1851 1859.
 
(101) A. Gotte. Die Entivicklungsgeschichte der Unkc. Leipzig, 1875.
 
(102) C. K. Hoffmann. "Amphibia." Klassen u. Ordnungen d. T/iierrdchs,
18731879.
 
(103) T. H. Huxley. Article "Amphibia in the Encyclopedia Jintannica.
 
(104) A. Moquin-Tandon. "Developpement des Batraciens anures." Annales
des Sciences Naturelles, III. 1875.
 
(105) G. Newport. " On the impregnation of the Ovum in Amphibia " (three
memoirs). Phil. Trans. 1851, 1853, and 1854.
 
(106) W. K. Parker. " On the structure and development of the Skull of the
common Frog." Phil. Trans., CLXI. 1871.
 
(107) W. K. Parker. " On the structure and development of the Skull of the
Batrachia." Phil. Trans., Vol. CXLVI., Part 2. 1876.
 
(108) W. C. H. Peters. " Ueber die Entwicklung der Coecilien und besonders
von Coecilia compressicauda." Berlin. Monatsbericht, p. 40, 1874.
 
(109) W. C. H. Peters. "Ueber die Entwicklung der Coecilien." Berl.
Monalsbericht, p. 483, 1875.
 
(110) J. L. Prevost and J. B. Dumas. " Deuxieme Mem. s. 1. generation.
Developpement de 1'ceuf d. Batraciens." Ann. Set. Nat. II. 1824.
 
(111) R. Remak. Untersuchungm iiber die Entwicklung der Wirbelthicn;
18501858.
 
(112) M. Rusconi. Developpement de la grenouille commune depuis le moment de
sa naissance jusqu ' son etat parfait, 1826.
 
(113) M. Rusconi. Histoire naturelle, developpement et metamorphose de la
Salamandre terrestre, 1854.
 
(114) W. B. Scott and H. F. Osborn. "On the early development of the
common Newt." Quart. J. of Micr. Science, Vol. xxix. 1879.
 
(115) S. Strieker. " Entwicklungsgeschichte von Bufo cinereus." Sitzb. der
kaiserl. Acad. zu Wien, 1860.
 
(116) S. Strieker. " Untersuchungen iiber die ersten Anlagen in BatrachierEiern." Zeitschrift f. wiss. Zoologie, Bd. xi. 1861.
 
 
 
AVES.
 
(117) K. E. vonBaer. " Ueb. Entwickhmgsgeschichte d. Thiere." Konigsberg,
18281837.
 
(118) F. M. Balfour. "The development and growth of the layers of the
Blastoderm," and "On the disappearance of the Primitive Groove in the Embryo
Chick." Quart. J. of Micros. Science, Vol. xin. 1873.
 
(119) M. Braun. " Die Entwicklung d. Wellenpapagei's." Parti. Arbeit, d.
zool.-zoot. Instit. Wiirzburg. Vol. V. 1879.
 
(120) M. Braun. "Aus d. Entwick. d. Papageien; I. Riickenmark ; II.
Entwicklung d. Mesoderms; III. Die Verbindungen zwischen Riickenmark u. Darm
bei Vogeln." Verh. d. phys.-med. Ges. zu Wurzbtirg. N. F. Bd. XIV. and xv. 1879
and 1880.
 
(121) J. Disse. " Die Entwicklung des mittleren Keimblattes im Htirmerei.
Archiv fur mikr. Anat., Vol. xv. 1878.
 
(122) J. Disse. "Die Entstehung d. Blutes u. d. ersten Gefasse im Hiihnerei.'
Archiv f. mikr. Anat., Vol. xvi. 1879.
 
(123) Fr. Durante. "Sulla struttura della macula germinativa delle uova di
Gallina." Ricerche nel Laboratorio di Anatomia della R. Universita di Roma.
 
(124) E. Dursy. Der Primitivstreif des Hiihnchens. 1867.
 
(125) M. Duval. "Etude sur la ligne primitive de 1'embryon de Poulet.
Annales des Sciences Naturelles, Vol. vn. 1879.
 
(126) M. Foster and F. M. Balfour. Elements of Embryology. Part I.
London, 1874.
 
 
 
vi BIBLIOGRAPHY.
 
 
 
(127) Gasser. "Der Primitivstreifen bei Vogelembryonen." Schrifteti d.
Gescll. zur Befbrd. d. gesammten Naturwiss. zu Marburg, Vol. II. Supplement l.
1879.
 
(128) A. Gotte. " Beitrage zur Entwicklungsgeschichte d. Wirbelthiere. II.
Die Bildung d. Keimblatter u. d. Blutes im Hiihnerei." Archiv fiir mikr. Anat.,
Vol. x. 1874.
 
(129) V. Hensen. " Embryol. Mitth." Archiv f. mikr. Anat., Vol. in.
1867.
 
(130) W. His. Untersuch. iib. d. erste Anlage d, Wirbelthierleibes. Leipzig,
1868.
 
(131) W. His. Unsere Kbrperform tmd das physiol. Problem ihrer Entstehung.
Leipzig, 1875.
 
(132) W. His. "Der Keimwall des Hiihnereies u. d. Entstehung d. parablastischen Zellen." Zeit.f. Anat.u. Entwicklungsgeschichte. Bd. I. 1876.
 
(133) W. His. " Neue Untersuchungen iib. die Bildung des Hiihnerembryo I."
Archiv f. Anat. u. Phys. 1877.
 
(134) E. Klein. "Das mittlere Keimblatt in seiner Bezieh. z. Entwick. d. ers.
Blutgefiisse und Blutkorp. im Hiihnerembryo." Sitzungsber. Wien. Akad., Vol. LXIII.
1871.
 
(135) A. K6 Hiker. Entwicklungsgeschichte d. Menschen u. d. hbheren 7'hii'rc.
Leipzig, 1879.
 
(136) C. Kupffer. " Die Entsteh. d. Allantois u. d. Gastrula d. Wirbelth."
Zoolog. Anzeiger, Vol. II. 1879, PP- 5 2O > 593> 612.
 
(137) C. Kupffer and B. Benecke. " Photogramme z. Ontogenie d.
Vogel." Nov. Act. d. k. Leop.-Carol.-Deutschen Akad. d. Naturforscher, Vol. XLI.
1879.
 
(138) J. Oellacher. "Untersuchungen tiber die Furchung u. Blatterbildung
im Hiihnerei." Strieker's Studien. 1870.
 
(139) C. H. Pander. Beitrage z. Entwick. d. Hiinchens im Eie. Wiirzburg,
1817.
 
(140) A. Rauber. " Ueber die Etnbryonalanlage des Hiihnchens." Centralblatt
fur d. medic. Wissenschaften. 1874 75.
 
(141) A. Rauber. Ueber die Stellung des Hiihnchens im Entwickhingsplan.
1876.
 
(142) A. Rauber. " Primitivrinne und Urmund. Beitrage zur Entwicklungsgeschichte des Hiihnchens." Morphol. Jahrbuch, B. II. 1876.
 
(143) A. Rauber. Primitivslreifen und Neurula der Wirbelthiere in normalcr
und pathologischer Beziehung. 1877.
 
(144) R. Remak. Untersuch. iib. d. Entwicklung d. Wirbelthiere. Berlin,
185055.
 
(145) S. L. Schenk. "Beitrage z. Lehre v. d. Organanlage im motorischen
Keimblatt.'' Sitz. Wien. Akad., Vol. LVII. 1860.
 
(146) S. L. Schenk. " Beitrage z. Lehre v. Amnion." Archiv f. mikr. Anat.,
Vol. vii. 1871.
 
(147) S. L. Schenk. Lehrbuch d. vergleich. Embryol. d. Wirbelthiere. Wien,
1874.
 
(148) S. Strieker. " Mittheil. iib. d. selbststiindigen Bewegungen embryonaler
Zellen." Sitz. Wien. Akad., Vol. XLIX. 1864.
 
(149) S. Strieker. "Beitrage zur Kenntniss des Hiihnereies." Wiener Sitzungsber., Vol. LIV. 1866.
 
(150) H. Virchow. Ueber d. Epithel d. Dottersackes im Hiihnerei. Inaug.
Diss. Berlin, 1875.
 
(151) W. Waldeyer. "Ueber die Keimblatter und den Primitivstreifen bei
der Entwicklung des Hiihnerembryo." Zeitschrift fiir ratioudle Medicin. 1869.
 
(152) C. F. Wolff. Theoria generationis. Halse, 1759.
 
(153) C. F. Wolff. Ueb. d. Bildung d. Darmcanals im bebriitcten Hiinchen.
Halle, 1812.
 
REPTILIA.
 
(154) C. Kupffer and Benecke. Die erste Entwicklung am Ei d. Keptilien.
Konigsberg, 1878.
 
 
 
BIBLIOGRAPHY, vii
 
 
 
(155) C. Kupffer. "Die Entstehung d. Allantois u. <1. Gastrula d. Wirbclthiere." Zoologischer Anzeiger, Vol. II. 1879, pp. 520, 593, 612.
 
Lacertilia.
 
(156) F. M. Balfour. " On the early Development of the Lacertilia, together
with some observations, etc." Quart. J. of Micr. Science, Vol. xix. 1879.
 
(157) Emmert u. Hochstetter. " Untersuchung lib. d. Entwick. d. Eidechsen
in ihren Eiern." Reil's Archiv, Vol. X. 1811.
 
(158) M. Lereboullet. "Developpement de la Truite, du Lc/ard et du
Limnee. II. Embryologie du Lezard." An. Sci. Nat., Ser. iv., Vol. xxvn.
1862.
 
(159) W. K. Parker. "Structure and Devel. of the Skull in Lacertilia.''
Phil. Trans., Vol. 170, p. 2. 1879.
 
(160) H. Strahl. " Ueb. d. Canalis myeloentericus d. Eidechse." Schrift. d.
Gesell. z. Be/or, d. gesam. Naturwiss. Marburg. July 23, 1880.
 
Ophidia.
 
(161) H. Dutrochet. " Recherches s. 1. en veloppes du foetus." Mem. d. Soc.
Mcd. if Emulation, Paris, Vol. vm. 1.816.
 
(162) W. K. Parker. "On the skull of the common Snake." Phil. Trans. ,
Vol. 169, Part II. 1878.
 
(163) H. Rathke. EntTvick. d. Natter. Konigsberg, 1839.
 
Chelonia.
 
(164) L. Agassiz. Contributions to the Natural History of the United Slates,
Vol. u. 1857. Embryology of the Turtle.
 
(165) W. K. Parker. "On the development of the skull and nerves in the
green Turtle." Proc. of the Roy. Soc., Vol. xxvin. 1879. Vide also Nature,
April 14, 1879, and Challenger Reports, Vol. I. 1880.
 
(166) H. Rathke. Ueb. d. Entwicklung d. Schildkroten. Braunschweig, 1848.
 
Crocodilia.
 
(167) H. Rathke. Ueber die Entwicklung d. Krokodile. Braunschweig, 1866.
 
MAMMALIA.
 
(168) K. E. von Baer. Ueb. Entwicklungsgcschichte d. Jhiere. Konigsberg,
 
(169) Barry. "Researches on Embryology." First Series. Philosophical
Transactions, 1838, Part II. Second Series, Ibid. 1839, Part II. Third Series, Ibid.
1840.
 
(170) Ed. van Beneden. La maturation de Foeuf, la fecondation et les premieres
phases du developpement embryonaire d. Mammiferes. Bruxelles, 1875.
 
(171) Ed. van Beneden. " Recherches sur 1'embryologie des Mammiferes.
Archives de Biologic, Vol. I. 1880.
 
(172) Ed. v. Beneden and Ch. Julin. "Observations sur la maturation etc.
de 1'oeuf chez les Cheiropteres." Archives de Biologie, Vol. I. 1880.
 
(173) Th. L. W. Bischoff. Entivicklungsgeschichte d. Siiugethiere 11. des
Menschcn. Leipzig, 1842.
 
(174) Th. L. W. Bischoff. Entivicklungsgeschichte des Kanmcheneies. Braunschweig, 1842.
 
(175) Th. L. W. Bischoff. Entwicklungsgeschuhte des Hundeeies.
 
schweig, 1845.
 
(176) Th. L. W. Bischoff. Entivicklungsgesclnchte des Meerschivcinchens.
 
Giessen. 1852.
 
 
 
viii BIBLIOGRAPHY.
 
 
 
(177) Th. L. W. Bischoff. Entivicklungsgeschichte des Rehcs. Giesscn, 1854.
 
(178) Th. L. W. Bischoff. " Neue Beobachtungen z. Entwicklungsgesch. des
Meerschweinchens." Abh. d. bayr. Akad., Cl. n. Vol. X. 1866.
 
(179) Th. L. W. Bischoff. Historisch-kritische B enter kungen z. d. naicstcn
Alittheilungen iil>. d. erste Entwick. d. Siitigethiereier. Miinchen, 1877.
 
(180) M. Coste. Embryogenie comparee. Paris, 1837.
 
(181) E. Haeckel. Anthropogenie, Entwicklungsgeschichte des Menschen.
Lci])zig, 1874.
 
(182) V. Hensen. "Beobachtungen lib. d. Befrucht. u. Entwick. d. Kaninchens
u. Meerschweinchens." Zeit.f. Anat. u. Entwick., Vol. I. 1876.
 
(183) A. Kolliker. Entivicklungsgeschichte d. Menschen u. d. hb'hcren Thiere.
Leipzig, 1879.
 
(184) A. Kolliker. "Die Entwick. d. Keimblatter des Kaninchens." Zoologist her Anseiger, Nos. 61, 62, Vol. in. 1880.
 
(185) N. Lieberkiihn. Ueber d. Keimblatter d. Siiugethiere. Doctor- Jubelfeier
d. Herrn H. Nasse. Marburg, 1879.
 
(186) N. Lieberkiihn. "Z. Lehre von d. Keimblattern d. Saugethiere." Sitz.
d. Gesell. z. Beford. d. gesam. Natunviss. Marburg, No. 3. 1880.
 
(187) Rauber. "Die erste Entwicklung d. Kaninchens." Sitzungsber. d.
naturfor. Gesell. z. Leipzig. 1875.
 
(188) C. B. Reichert. " Entwicklung des Meerschweinchens." Abh. der.
Berl. Akad. 1862.
 
(189) E. A. S chafer. " Description of a Mammalian ovum in an early condition of development." Proc. Roy. Soc., No. 168. 1876.
 
(190) E. A. Schafer. "A contribution to the history of development of the
guinea-pig." Journal of Anal, and Phys. , Vol. x. and xi. 1876 and 1877.
 
Fcetal Membranes and Placenta of Mammalia.
 
(191) John Anderson. Anatomical and Zoological Researches in Western
Yunnan. London, 1878.
 
(192) K. E. von Baer. Untersuchungen iiber die Gef&ssverbindung zwischen
Mutter und Fruc/tf, 1828.
 
(193) C. G. Cams. Tabulae anatomiam comparali-vam illustrantes. 1831,
1840.
 
(194) H. C. Chapman. "The placenta and generative apparatus of the
Elephant." Journ. Acad. Nat. Sc., Philadelphia. Vol. viii. 1880.
 
(195) C. Creighton. " On the formation of the placenta in the guinea-pig."
Journal of Anat. and Phys., Vol. XII. 1878.
 
(196) Ecker. Icones Physiologicae. 1852-1859.
 
(197) G. B. Ercolani. 7'he utricular glands of the uterus, etc., translated from
the Italian under the direction of H. O. Marcy. Boston, 1880. Contains translations
of memoirs published in the Mem. deW Accad. d. Scienze d. Bologna, and additional
matter written specially for the translation.
 
(198) G. B. Ercolani. Nuove ricerche sulla placenta nei pesci cartilaginosi e
nei mammiferi. Bologna, 1 880.
 
(199) Eschricht. De organis quae respirationi et mttritioni fcetus Mammaliutn
inservinnt. Hafniae, 1837.
 
(200) A. H. Gar rod and W. Turner. "The gravid uterus and placenta of
Hyomoschus aquaticus." Proc. Zool. Soc., London, 1878.
 
(201) P. Hart ing. Het ei en de placenta van Halicore Dugong. Inaug. diss.
Utrecht. " On the ovum and placenta of the Dugong." Abstract by Prof. Turner.
Journal of Anat. and Phys., Vol. xin.
 
(202) Th. H. Huxley. The Elements of Comparative Anatomy. London,
1864.
 
(203) A. Kolliker. " Ueber die Placenta der Gattung Tragulus." Verh. der
Wiirzb. phys.-med. Gesellschaft, Bd. x.
 
(204) C. D. Meigs. "On the reproduction of the Opossum (Didelphis Virginiana)." Amer. Phil. Soc. Trans., Vol. x. 1853.
 
(205) H.Milne-Edwards. " Sur la Classification Naturelle." Ann. Sciences
Nat., Ser. 3, Vol. I. 1844.
 
 
 
BIBLIOGRAPHY.
 
 
 
IX
 
 
 
(206) Alf. Milne-Edwards. "Kecherches sur la famille dcs Chcvrutains.' 1
Ann. dcs Sciences Nat., Series V., Vol. II. 1864.
 
(207) Alf. Milne-Edwards. " Observations sur quelqucs points <le I'Kmbryologie des Lemuriens, etc." Ann. Sci. Nat., Ser. V., Vol. xv. 1872.
 
(208) Alf. Milne-Edwards. " Sur la conformation du placenta chcz le Tainandua." Ann. des Sci. Nat., xv. 1872.
 
(209) Alf. Milne-Edwards. " Kecherches s. 1. enveloppes fcetales du Tatou a
neuf bandes." Ann. Sci. Nat., Ser. vi., Vol. vill. 1878.
 
(210) R. Owen. "On the generation of Marsupial animals, with a description
of the impregnated uterus of the Kangaroo." Phil. Trans., 1834.
 
(211) R. Owen. "Description of the membranes of the uterine foetus of the
Kangaroo." Mag. Nat. Hist., Vol. I. 1837.
 
(212) R. Owen. "On the existence of an Allantois in a foetal Kangaroo
(Macropus major)." Zool. Soc. Proc., v. 1837.
 
(213) R. Owen. "Description of the foetal membranes and placenta of the
Elephant." Phil. Trans., 1857.
 
(214) R.Owen. On the Anatomy of Vertebrates, Vol. III. London, 1868.
 
(215) G. Rolleston. " Placental structure of the Tenrec, etc." Transactions
of the Zoological Society, Vol. V. 1866.
 
(216) W. Turner. "Observations on the structure of the human placenta."
Journal of Anat. and Phys., Vol. vn. 1868.
 
(217) W. Turner. "On the placentation of the Cetacea." Trans. Roy. Soc.
Edinb,, Vol. xxvi. 1872.
 
(218) W. Turner. "On the placentation of Sloths (Cholcepus Hoffrnanni)."
Trans, of R. Society of Edinburgh, Vol. xxvn. 1875.
 
(219) W. Turner. "On the placentation of Seals (Halichcerus gryphus)."
Trans, of R. Society of Edinburgh, Vol. xxvii. 1875.
 
(220) W.Turner. "On the placentation of the Cape Ant-eater (Orycteropus
capensis)." Journal of Anat. and Phys., Vol. X. 1876.
 
(221) W. Turner. Lectures on the Anatomy of the Placenta. First Series.
Edinburgh, 1876.
 
(222) W. Turner. "Some general observations on the placenta, with special
reference to the theory of Evolution." Journal of Anat. and Phys., Vol. XI. 1877.
 
(223) W.Turner. " On the placentation of the Lemurs." Phil. Trans., Vol.
166, p. 2. 1877.
 
(224) W.Turner. " On the placentation of Apes." Phil. Trans., 1878.
 
(225) W. Turner. "The cotyledonary and diffused placenta of the Mexican
deer (Cervus Americanus). " Journal of Anat. and Phys., Vol. xm. 1879.
 
 
 
Human Embryo.
 
(226) Fried. Ahlfeld. " Beschreibung eines sehr kleinen menschlichen Eies."
Archiv f. Gynaekologie, Bd. xm. 1878.
 
(227) Herm. Beigel und Ludwig Loewe. "Beschreibung eines menschlichen
Eichens aus der zweiten bis dritten Woche der Schwangerschaft." Archiv f. Gynaekologie, Bd. xn. 1877.
 
(228) K. Breus. " Ueber ein menschliches Ei aus der zweiten Woche der
Graviditat." Wiener medicinische Wochenschrift, 1877.
 
(229) M. Coste. Histoire generale et particuliere du developpement des corps organises, 1847-59.
 
(230) A. Ecker. Icones Physiologicae. Leipzig, 1851-1859.
 
(231) V. Hensen. " Beitrag z. Morphologic d. Korperform u. d. Gehirns d.
menschlichen Embryos." Archiv f. Anat. u. Phys., 1877.
 
(232) W. His. Anatomie menschlicher Etnbryonen, Part I. Embryonen d.
ersten Monats. Leipzig, 1880.
 
(233) J. Kollmann. " Die menschlichen Eier von 6 MM. Grosse." Archiv f.
 
 
 
Anat. und Phys., 1879.
 
(234) W. Krause.
Phys., 1875.
 
(235) W. Krause.
/. wiss. Zool., Vol. xxxv.
 
 
 
Ueber d. Allantois d. Menschen." Archiv f. Anat. und
 
 
 
' Ueber zwei friihzeitige menschliche Embryonen."
1880.
 
 
 
Zeit.
 
 
 
X BIBLIOGRAPHY.
 
 
 
(236) L. Loewe. "Im Sachen cler Eihaute jiingster menschlicher Eicr. "
Archiv fiir Gynaekologie, Bd. xiv. 1879.
 
(237) C. B. Reichert. " Beschreibung einer friihzeitigen menschlichcn Frucht
im blaschenformigen Bildungszustande (sackformiger Keim von Baer) nebst vergleichenden Untersuchungen iiber die blaschenformigen Friichte der Saugethiere und des
Menschen. " Abhandlungcn der konigl. Akad. d, Wiss, zu Berlin, 1873.
 
(238) Allen Thomson. "Contributions to the history of the structure of the
human ovum and embryo before the third week after conception ; with a description
of some early ova." Edinburgh Med. Siirg.Journal, Vol. LI I. 1839.
 
COMPARISON OF THE FORMATION OF THE GERMINAL LAYERS
IN THE VERTEBRATA.
 
(239) F. M. Balfour. "A comparison of the early stages in the development
of Vertebrates." Quart. J. of Micr. Science, Vol. xv. 1875.
 
(240) F. M. Balfour. "A monograph on the development of Elasmobranch
Fishes." London, 1878.
 
(241) F. M. Balfour. " On the early development of the Lacertilia together
with some observations, etc." Quart. J. of Micr. Science, Vol. xix. 1879.
 
(242) A. Gotte. Die Entwicklungsgeschichte d. Unke. Leipzig, 1875.
 
(243) W. His. "Ueb. d. Bildung d. Haifischembryonen." Zeit. f. Anal. it.
Entwick., Vol. II. 1877. Cf. also His' papers on Teleostei, Nos. 65 and 66.
 
(244) A. Kowalevsky. " Entwick. d. Amphioxus lanceolatus." Mem. Acad.
des Sciences St Petersbourg, Ser. vii. Tom. XI. 1867.
 
(245) A. Kowalevsky. " Weitere Studien lib. d. Entwick. d. Amphioxus lanceolatus." Archiv f. mikr. Anal., Vol. XIII. 1877.
 
(246) C. Kupffer. "Die Entstehung d. Allantois u. d. Gastrula d. Wirbelthiere." Zool. Anzeiger, Vol. II. 1879, PP- 5 2 ' 593' 61?.
 
(247) R. Remak. Untersuchungen iib. d. Entiuicklung d. Wirbelthiere, 1850
1858.
 
(248) A. Rauber. Primitivstreifen ti. Neurula d. Wirbelthiere, Leipzig,
1877.
 
PHYLOGENY OF THE CHORDATA.
 
(249) F. M. Balfour. A Monograph on the development of Elasmobranch Fishes,
London, 1878.
 
(250) A. Dohrn. Der Ursprung d. Wirbelthiere und d. Princip. d. Functionswechsel. Leipzig, 1875.
 
(251) E. Haeckel. Schb'pfungsgeschichte. Leipzig. Vide also Translation.
The History of Creation. King and Co. , London. 1876.
 
(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.
 
 
 
 
 
{{Footer}}
[[Category:Historic Embryology]][[Category:1800's]]

Latest revision as of 16:53, 27 February 2019

Embryology - 30 Apr 2024    Facebook link Pinterest link Twitter link  Expand to Translate  
Google Translate - select your language from the list shown below (this will open a new external page)

العربية | català | 中文 | 中國傳統的 | français | Deutsche | עִברִית | हिंदी | bahasa Indonesia | italiano | 日本語 | 한국어 | မြန်မာ | Pilipino | Polskie | português | ਪੰਜਾਬੀ ਦੇ | Română | русский | Español | Swahili | Svensk | ไทย | Türkçe | اردو | ייִדיש | Tiếng Việt    These external translations are automated and may not be accurate. (More? About Translations)

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
Online Editor 
Mark Hill.jpg
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.
Modern Notes:

Historic Disclaimer - information about historic embryology pages 
Mark Hill.jpg
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)


Draft Version - Notice removed when completed.

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

Chapter XXIII. Excretory Organs

Excretory organs consist of coiled or branched and often ciliated tubes, with an excretory pore opening on the outer surface of the body, and as a rule an internal ciliated orifice placed in the body-cavity. In forms provided with a true vascular system, there is a special development of capillaries around the glandular part of the excretory organs. In many instances the glandular cells of the organs are filled with concretions of uric acid or some similar product of nitrogenous waste.

There is a very great morphological and physiological similarity between almost all the forms of excretory organ found in the animal kingdom, but although there is not a little to be said for holding all these organs to be derived from some common prototype, the attempt to establish definite homologies between them is beset with very great difficulties.

Platyelminthes. Throughout the whole of the Platyelminthes these organs are constructed on a well-defined type, and in the Rotifera excretory organs of a similar form to those of the Platyelminthes are also present.

These organs (Fraipont, No. 513) are more or less distinctly paired, and consist of a system of wide canals, often united into a network, which open on the one hand into a pair of large tubes leading to the exterior, and on the other into fine canals which terminate by ciliated openings, either in spaces between the connective-tissue cells (Platyelminthes), or in the body-cavity (Rotifera). The fine canals open directly into the larger ones, without first uniting into canals of an intermediate size.


EXCRETORY ORGANS.


68 1


The two large tubes open to the exterior, either by means of a median posteriorly placed contractile vesicle, or by a pair of vesicles, which have a ventral and anterior position. The former type is characteristic of the majority of the Trematoda, Cestoda. and Rotifera, and the latter of the Nemertea and some Trematoda. In the Turbellaria the position of the external openings of the system is variable, and in a few Cestoda (Wagner) there are lateral openings on each of the successive proglottides, in addition to the terminal openings. The mode of development of these organs is unfortunately not known.

Mollusca. In the Mollusca there are usually present two independent pairs of excretory organs one found in a certain number of forms during early larval life only 1 , and the other always present in the adult.

The larval excretory organ has been found in the pulmonate Gasteropoda (Gegenbaur, Fol 2 , Rabl), in Teredo (Hatschek), and possibly also in Paludina. It is placed in the anterior region of the body, and opens ventrally on each side, a short way behind the velum. It is purely a larval organ, disappearing before the close of the veliger stage. In the aquatic Pulmonata, where it is best developed, it consists on each side of a V-shaped tube, with a dorsally-placed apex, containing an enlargement of the lumen. There is a ciliated cephalic limb, lined by cells with concretions, and terminating by an internal opening near the eye, and a nonciliated pedal limb opening to the exterior 3 .

Two irreconcilable views are held as to the development of this system. Rabl (Vol. II. No. 268) and Hatschek hold that it is developed in the mesoblast ; and Rabl states that in Planorbis it is formed from the anterior mesoblast cells of the mesoblastic bands. A special mesoblast cell on each side elongates into two processes, the commencing limbs of the future organ. A lumen is developed in this cell, which is continued into each limb, while

1 I leave out of consideration an external renal organ found in many marine Gasteropod larvte, vide Vol. II. p. 280.

2 H. Fol, "Etudes sur le devel. d. Mollusques. " Mem. Hi. Archiv d. Zool. exfJr. et gener., Vol. VIII.

3 The careful observations of Fol seem to me nearly conclusive in favour of this limb having an external opening, and the statement to the reverse effect on p. 280 of Vol. ii. of this treatise, made on the authority of Rabl and Biitschli, must probably be corrected.


682 POLYZOA.

the continuations of the two limbs are formed by perforated mesoblast cells.

According to Fol these organs originate in aquatic Pulmonata as a pair of invaginations of the epiblast, slightly behind the mouth. Each invagination grows in a dorsal direction, and after a time suddenly bends on itself, and grows ventralwards and forwards. It thus acquires its V-shaped form.

In the terrestrial Pulmonata the provisional excretory organs are, according to Fol, formed as epiblastic invaginations, in the same way as those in the aquatic Pulmonata, but have the form of simple non-ciliated sacks, without internal openings.

The permanent renal organ of the Mollusca consists typically of a pair of tubes, although in the majority of the Gasteropoda one of the two tubes is not developed. It is placed considerably behind the provisional renal organ.

Each tube, in its most typical form, opens by a ciliated funnel into the pericardial cavity, and has its external opening at the side of the foot. The pericardial funnel leads into a glandular section of the organ, the lining cells of which are filled with concretions. This section is followed by a ciliated section, from which a narrow duct leads to the exterior.

As to the development of this organ the same divergence of opinion exists as in the case of the provisional renal organ.

Rabl's careful observations on Planorbis (Vol. II. No. 268) tend to shew that it is developed from a mass of mesoblast cells, near the end of the intestine. The mass becomes hollow, and, attaching itself to the epiblast on the left side of the anus, acquires an opening to the exterior. Its internal opening is not established till after the formation of the heart. Fol gives an equally precise account, but states that the first rudiment of the organ arises as a solid mass of epiblast cells. Lankester finds that this organ is developed as a paired invagination of the. epiblast in Pisidium, and Bobretzky also derives it from the epiblast in marine Prosobranchiata. In Cephalopoda on the other hand Bobretzky's observations (I conclude this from his figures) indicate that the excretory sacks of the renal organs are derived from the mesoblast.

Polyzoa. Simple excretory organs, consisting of a pair of ciliated canals, opening between the mouth and the anus, have


EXCRETORY ORGAN>.


68 3


been found by Hatschek and Joliet in the Entoproctous Polyzoa, and are developed, according to Hatschek, by whom they were first found in the larva, from the mesoblast

Brachiopoda. One or rarely two (Rhynchonella) pairs of canals, with both peritoneal and external openings, are found in the Brachiopoda. They undoubtedly serve as genital ducts, but from their structure are clearly of the same nature as the excretory organs of the Chaetopoda described below. Their development has not been worked out.

Chaetopoda. Two forms of excretory organ have been met with in the Chaetopoda. The one form is universally or nearly universally present in the adult, and typically consists of a pair of coiled tubes repeated in every segment. Each tube has an internal opening, placed as a rule in the segment in front of that in which the greater part of the organ and the external opening are situated.

There are great variations in the structure of these organs, which cannot be dealt with here. It may be noted however that the internal opening may be absent, and that there may be several internal openings for each organ (Polynoe). In the Capitellidae moreover several pairs of excretory tubes have been shewn by Eisig (No. 512) to be present in each of the posterior segments.

The second form of excretory organ has as yet only been found in the larva of Polygordius, and will be more conveniently dealt with in connection with the development of the excretory system of this form.

There is still considerable doubt as to the mode of formation of the excretory tubes of the Chaetopoda. Kowalevsky (No. 277), from his observations on the Oligochasta, holds that they develop as outgrowths of the epithelial layer covering the posterior side of the dissepiments, and secondarily become connected with the epidermis.

Hatschek finds that in Criodrilus they arise from a continuous linear thickening of the somatic mesoblast, immediately beneath the epidermis, and dorsal to the ventral band of longitudinal muscles. They break up into S-shaped cords, the anterior end of each of which is situated in front of a dissepiment, and is formed at first of a single large cell, while the posterior part is


684 CHvETOPODA.


continued into the segment behind. The cords are covered by a peritoneal lining, which still envelopes them, when in the succeeding stage they are carried into the body-cavity. They subsequently become hollow, and their hinder ends acquire openings to the exterior. The formation of their internal openings has not been followed.

Kleinenberg is inclined to believe that the excretory tubes take their origin from the epiblast, but states that he has not satisfactorily worked out their development.

The observations of Risig (No. 512) on the Capitellidae support Kowalevsky's view that the excretory tubes originate from the lining of the peritoneal cavity.

Hatschek (No. 514) has given a very interesting account of the development of the excretory system in Polygordius.

The excretory system begins to be formed, while the larva is still in the trochospere stage (fig. 383, npli), and consists of a provisional excretory organ, which is placed in front of the future segmented part of the body, and occupies a position very similar to that of the provisional excretory organ found in some Molluscan larvae (vide p. 68 1).

Hatschek, with some shew of reason, holds that the provisional excretory organs of Polygordius are homologous with those of the Mollusca.

In its earliest stage the provisional excretory organ of Polygordius consists of a pair of simple ciliated tubes, FIG. 383. POLYOORDIUS

, . , r 11-1 LARVA. (After Hatschek.)

each with an anterior funnel-like open- m _ moulh . ^ supraKBSO .

ing situated in the midst of the meSO- phageal ganglion ; nph. nephri11 11 . , dion ; ine.p. mesoblastic band;

blast cells, and a posterior external an _ anus 5 oL stomach . opening. The latter is placed immediately in front of what afterwards becomes the segmented region of the embryo. While the larva is still unsegmented, a second internal opening is formed for each tube (fig. 383, np/i) and the two openings so formed may eventually become divided into five (fig. 384 A), all communicating by a single pore with the exterior.

When the posterior region of the embryo becomes segmented,



EXCRETORY ORGANS.


685


paired excretory organs are formed in each of the posterior segments, but the account of their development, as given by Hatschek, is so remarkable that I do not think it can be definitely accepted without further confirmation.

From the point of junction of the two main branches of the larval kidney there grows backwards (fig. 384 B), to the hind end of the first segment, a very delicate tube, only indicated by its ciliated lumen, its walls not being differentiated. Near the front end of this tube a funnel, leading into the larval body cavity of the head, is formed, and subsequently the posterior end of the tube acquires an external opening, and the tube distinct walls. The communication with the provisional excretory organ is then lost, and thus the excretory tube of the first segment is established.

The excretory tubes in the second and succeeding segments are formed in the same way as in the first, i.e. by the continuation of the lumen of the hind end of the excretory tube from the preceding segment, and the subsequent separation of this part as a separate tube.

The tube may be continued with a sinuous course through



A A

A +

A.


Y

Y Y Y Y


J)


FIG. 384. DIAGRAM ILLUSTRATING THE DEVELOPMENT OF THE EXCRETORY SYSTEM OF POLYGORDIUS. (After Hatschek.)

several segments without a distinct wall. The external and internal openings of the permanent excretory tubes are thus secondarily acquired. The internal openings communicate with the permanent body-cavity. The development of the perma


686 GEPHYREA.


nent excretory tubes is diagrammatically represented in fig. 384 C and D.

The provisional excretory organ atrophies during larval life.

If Hatschek's account of the development of the excretory system of Polygordius is correct, it is clear that important secondary modifications must have taken place in it, because his description implies that there sprouts from the anterior excretory organ, while it has its own external opening, a posterior duct, which does not communicate either with the exterior or with the body-cavity! Such a duct could have no function. It is intelligible either (i) that the anterior excretory organ should lead into a longitudinal duct, opening posteriorly ; that then a series of secondary openings into the body-cavity should attach themselves to this, that for each internal opening an external should subsequently arise, and the whole break up into separate tubes ; or (2) that behind an anterior provisional excretory organ a series of secondary independent segmental tubes should be formed. But from Hatschek's account neither of these modes of evolution can be deduced.

Gephyrea. The Gephyrea may have three forms of excretory organs, two of which are found in the adult, and one, similar in position and sometimes also in structure, to the provisional excretory organ of Polygordius, has so far only been found in the larvae of Echiurus and Bonellia.

In all the Gephyrea the so-called 'brown tubes' are apparently homologous with the segmented excretory tubes of Chaetopods. Their main function appears to be the transportation of the generative products to the exterior. There is but a single highly modified tube in Bonellia, forming the oviduct and uterus ; a pair of tubes in the Gephyrea inermia, and two or three pairs in most Gephyrea armata, except Bonellia. Their development has not been studied.

In the Gephyrea armata there is always present a pair of posteriorly placed excretory organs, opening in the adult into the anal extremity of the alimentary tract, and provided with numerous ciliated peritoneal funnels. These organs were stated by Spengel to arise in Bonellia as outgrowths of the gut ; but in Echinrus Hatschek (No. 515) finds that they are developed from the somatic mesoblast of the terminal part of the trunk. They soon become hollow, and after attaching themselves to the epiblast on each side of the anus, acquire external openings. They are not at first provided with peritoneal funnels, but these parts of the organs become developed from a ring of cells at


EXCRETORY ORGANS.


687


their inner extremities ; and there is at first but a single funnel for each vesicle. The mode of increase of the funnels has not been observed, nor has it been made out how the organs themselves become attached to the hind-gut.

The provisional excretory organ of Echiurus is developed at an early larval stage, and is functional during the whole of larval life. It at first forms a ciliated tube on each side, placed in front of that part of the larva which becomes the trunk of the adult. It opens to the exterior by a fine pore on the ventral side, immediately in front of one of the mesoblastic bands, and appears to be formed of perforated cells. It terminates internally in a slight swelling, which represents the normal internal ciliated funnel. The primitively simple excretory organ becomes eventually highly complex by the formation of numerous branches, each ending in a slightly swollen extremity. These branches, in the later larval stages, actually form a network, and the inner end of each main branch divides into a bunch of fine tubes. The whole organ resembles in many respects the excretory organ of the Platyelminthes.

In the larva of Bonellia Spengel has described a pair of provisional excretory tubes, opening near the anterior end of the body, which are probably homologous with the provisional excretory organs of Echiurus (vide Vol. II., fig. 162 C, se).

Discophora. As in many of the types already spoken of, permanent and provisional excretory organs may be present in the Discophora. The former are usually segmentally arranged, and resemble in many respects the excretory tubes of the Chaetopoda. They may either be provided with a peritoneal funnel (Nephelis, Clepsine) or have no internal opening (Hirudo).

Bourne 1 has shewn that the cells surrounding the main duct in the medicinal Leech are perforated by a very remarkable network of ductules, and the structure of these organs in the Leech is so peculiar that it is permissible to state with due reserve their homology with the excretory organs of the Chaetopoda.

The excretory tubes of Clepsine are held by Whitman to be developed in the mesoblast.

1 "On the Structure of the Nephridia of the Medicinal Leech." Quart. J. of Micr. Science, Vol. XX. 1880.


688 ARTHROPODA.


There are found in the embryos of Nephelis and Hirudo certain remarkable provisional excretory organs the origin and history of which are not yet fully made out. In Nephelis they appear as one (according to Robin), or (according to Biitschli) as two successive pairs of convoluted tubes on the dorsal side of the embryo, which are stated by the latter author to develop from the scattered mesoblast cells underneath the skin. At their fullest development they extend, according to Robin, from close to the head to near the ventral sucker. Each of them is U-shaped, with the open end of the U forwards, each limb of the U being formed by two tubes united in front. No external opening has been clearly made out. Fiirbringer is inclined from his own researches to believe that they open laterally. They contain a clear fluid.

In Hirudo, Leuckart has described three similar pairs of organs, the structure of which he has fully elucidated. They are situated in the posterior part of the body, and each of them commences with an enlargement, from which a convoluted tube is continued for some distance backwards; the tube then turns forwards again, and after bending again upon itself opens to the exterior. The anterior part is broken up into a kind of labyrinthic network.

The provisional excretory organs of the Leeches cannot be identified with the anterior provisional organs of Polygordius and Echiurus.

Arthropoda. Amongst the Arthropoda Peripatus is the only form with excretory organs of the type of the segmental excretory organs of the Chsetopoda 1 .

These organs are placed at the bases of the feet, in the lateral divisions of the body-cavity, shut off from the main median division of the body-cavity by longitudinal septa of transverse muscles.

Each fully developed organ consists of three parts :

(i) A dilated vesicle opening externally at the base of a foot. (2) A coiled glandular tube connected with this, and subdivided again into several minor divisions. (3) A short terminal portion opening at one extremity into the coiled tube

1 Vide F. M. Balfour, " On some points in the Anatomy of Peripatus Capensis." Quart. J, of Micr. Science, Vol. XIX. 1879.


EXCRETORY ORGANS. 689


and at the other, as I believe, into the body cavity. This section becomes very conspicuous, in stained preparations, by the intensity with which the nuclei of its walls absorb the colouring matter.

In the majority of the Tracheata the excretory organs have the form of the so-called Malpighian tubes, which always (vide Vol. II.) originate as a pair of outgrowths of the epiblastic proctodaeum. From their mode of development they admit of comparison with the anal vesicles of the Gephyrea, though in the present state of our knowledge this comparison must be regarded as somewhat hypothetical.

The antennary and shell-glands of the Crustacea, and possibly also the so-called dorsal organ of various Crustacean larvae appear to be excretory, and the two former have been regarded by Claus and Grobben as belonging to the same system as the segmental excretory tubes of the Chaetopoda.

Nematoda. Paired excretory tubes, running for the whole length of the body in the so-called lateral line, and opening in front by a common ventral pore, are present in the Nematoda. They do not appear to communicate with the body cavity, and their development has not been studied.

Very little is known with reference either to the structure or development of excretory organs in the Echinodermata and the other Invertebrate types of which no mention has been so far made in this Chapter.

Excretory organs and generative ducts of the Craniata.

Although it would be convenient to separate, if possible, the history of the excretory organs from that of the generative ducts, yet these parts are so closely related in the Vertebrata, in some cases the same duct having at once a generative and a urinary function, that it is not possible to do so.

The excretory organs of the Vertebrata consist of three distinct glandular bodies and of their ducts. These are (i) a small glandular body, usually with one or more ciliated funnels opening into the body cavity, near the opening of which there projects into the body cavity a vascular glomerulus. It is situated very far forwards, and is usually known as the head 44


690 ELASMOBRANCHII.


kidney, though it may perhaps be more suitably called, adopting Lankester's nomenclature, the pronepliros. Its duct, which forms the basis for the generative and urinary ducts, will be called the segmented duct.

(2) The Wolffian body, which may be also called the mesonepJiros. It consists of a series of, at first, segmentally (with a few exceptions) arranged glandular canals (segmental tubes) primitively opening at one extremity by funnel-shaped apertures into the body cavity, and at the other into the segmental duct. This duct becomes in many forms divided longitudinally into two parts, one of which then remains attached to the segmental tubes and forms the Wolffian or mesonepJiric duct, while the other is known as the Milllerian dnct.

(3) The kidney proper or metanephros. This organ is only found in a completely differentiated form in the amniotic Vertebrata. Its duct is an outgrowth from the Wolrfian duct.

The above parts do not coexist in full activity in any living adult member of the Vertebrata, though all of them are found together in certain embryos. They are so intimately connected that they cannot be satisfactorily dealt with separately.

Elasmobranchii. The excretory system of the Elasmobranchii is by no means the most primitive known, but at the same time it forms a convenient starting point for studying the modifications of the system in other groups. The most remarkable peculiarity it presents is the absence of a pronephros. The development of the Elasmobranch excretory system has been mainly studied by Semper and myself.

The first trace of the system makes its appearance as a knob of mesoblast, springing from the intermediate cell-mass near the level of the hind end of the heart (fig. 385 K,pd). This knob is the rudiment of the abdominal opening of the segmental duct, and from it there grows backwards to the level of the anus a solid column of cells, which constitutes the rudiment of the segmental duct itself (fig. 385 B, pd). The knob projects towards the epiblast, and the column connected with it lies between the mesoblast and epiblast. The knob and column do not long remain solid, but the former acquires an opening into the body cavity (fig. 421, sd) continuous with a lumen, which


EXCRETORY ORGANS.


691


makes its appearance in the column (fig. 386, sd). The knob forms the only structure which can be regarded as a rudiment of the pronephros.


spn


spn



FlG. 385. TWO SECTIONS OF A PRISTIURUS EMBRYO WITH THREE VISCERAL

CLEFTS.

The sections illustrate the development of the segmental duct (pd) or primitive duct of the pronephros. In A (the anterior of the two sections) this appears as a solid knob (pd) projecting towards the epiblast. In B is seen a section of the column which has grown backwards from the knob in A.

spn. rudiment of a spinal nerve; me. medullary canal; ch. notochord; X. subnotochordal rod; mp. muscle-plate; mp' . specially developed portion of muscle-plate; ao. dorsal aorta ; pd. segmental duct ; so. somatopleure ; sp. splanchnopleure ; //. body cavity; ep. epiblast; al. alimentary canal.

While the lumen is gradually being formed, the segmental tubes of the mesonephros become established. They appear to arise as differentiations of the parts of the primitive lateral plates of mesoblast, placed between the dorsal end of the body cavity and the muscle-plate (fig. 386, st) 1 , which are usually known as the intermediate cell-masses.

The lumen of the segmental tubes, though at first very small, soon becomes of a considerable size. It appears to be established in the position of the section of the body cavity in the intermediate cell-mass, which at first unites the part of the body cavity in the muscle-plates with the permanent body cavity. The lumen of each tube opens at its lower end into the dorsal part of the body cavity (fig. 386, st}, and each tube curls obliquely

1 In my original account of the development I held these tubes to be invaginations of the peritoneal epithelium. Sedgwick (No. 549) was led to doubt the accuracy of my original statement from his investigations on the chick ; and from a re-examination of my specimens he arrived at the results stated above, and which I am now myself inclined to adopt.

442


692


ELASMOBRANCHII.


sp.c



backwards round the inner and dorsal side of the segmental duct, near which it at first ends blindly.

One segmental tube makes its appearance for each somite (fig. 265), commencing with that immediately behind the abdominal opening of the segmental duct, the last tube being situated a few segments behind the anus. Soon after their formation the blind ends of the segmental tubes come in contact with, and open into the segmental duct, and each of them becomes divided into four parts. These are (i) a section carrying the peritoneal opening, known as the peritoneal funnel, (2) a dilated vesicle into which this opens, (3) a coiled tubulus proceeding from (2), and terminating in (4) a wider portion opening into the segmental duct. At the same time, or shortly before this, each segmental duct unites with and opens into one of the horns of the cloaca, and also retires from its primitive position between the epiblast and mesoblast, and assumes a position close to the epithelium lining the body cavity (fig. 380, sd}. The general features of the excretory organs at this period are diagrammatically represented in the woodcut (fig. 387). In this fig. pd is the segmental duct and o its abdominal opening; s.t points to the segmental tubes, the finer details of whose structure are not represented in the diagram. The mesonephros thus forms at this period an elongated gland composed of a series of isolated coiled tubes, one extremity of each of which opens into the body cavity, and the other into the segmental duct, which forms the only duct of the system, and communicates at its front end with the body cavity, and behind with the cloaca.


FIG. 386. SECTION THROUGH THE TRUNK OF A SCYLLIUM EMBRYO SLIGHTLY YOUNGER THAN

28 F.

sp.c. spinal canal; W. white matter of spinal cord ; pr. posterior nerve-roots ; ch. notochord ; x. sub-notochordal rod ; ao. aorta ; nip, muscle-plate ; nip', 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 ; p.o. primitive generative cells.


EXCRETORY ORGANS. 693


The next important change concerns the segmental duct, which becomes longitudinally split into two complete ducts in the female, and one complete duct and parts of a second duct in the male. The manner in which this takes place is diagrammatically represented in fig. 387 by the clear line x, and in transverse section in figs. 388 and 389. The resulting ducts are (i) the Wolffian duct or mesonephric duct (wd\ dorsally, which remains continuous with the excretory tubules of the mesonephros, and ventrally (2) the oviduct or Miillerian duct in the female, and the rudiments of this duct in the male. In the



FIG. 387. DIAGRAM OF THE PRIMITIVE CONDITION OF THE KIDNEY IN AN

ELASMOBRANCH EMBRYO.

pd. segmental duct. It opens at o into the body cavity and at its other extremity into the cloaca; x. line along which the division appears which separates the segmental duct into the Wolffian duct above and the Miillerian duct below; s.t. segmental tubes. They open at one end into the body cavity, and at the other into the segmental duct.

female the formation of these ducts takes place (fig. 389) by a nearly solid rod of cells being gradually split off from the ventral side of all but the foremost part of the original segmental duct. This nearly solid cord is the Miillerian duct (pd}. A very small portion of the lumen of the original segmental duct is perhaps continued into it, but in any case it very soon acquires a wide lumen (fig. 389 A). The anterior part of the segmental duct is not divided, but remains continuous with the Mullerian duct, of which its anterior pore forms the permanent peritoneal opening 1 (fig. 387). The remainder of the segmental duct (after the loss of its anterior section, and the part split off from its ventral side) forms the Wolffian duct. The process of formation of these ducts in the male differs from that in the female chiefly

1 Five or six segmental tubes belong to the region of the undivided anterior part of the segmental duct, which forms the front end of the Mullerian duct ; but they appear to atrophy very early, without acquiring a definite attachment to the segmental duct.


694


ELASMOBRANCHIL


in the fact of the anterior undivided part of the segmental duct, which forms the front end of the Miillerian duct, being shorter,



trd/



FIG. 389. FOUR SECTIONS THROUGH THE ANTERIOR I'ART OF THE SEGMENTAL DUCT OF A FEMALE EMBRYO OF SCYLLIUM CANICULA.

The figure shews how the segmental duct becomes split into the Wolffian or mesonephric duct above, and Miillerian duct or oviduct below.

wd. Wolffian or mesonephric duct; od. Miillerian duct or oviduct ; sd. segmental duct.


FIG. 388. DIAGRAMMATIC REPRESENTATION OF A TRANSVERSE SECTION OF A

SCYLLIUM EMBRYO ILLUSTRATING THE FORMATION OF THE WOLFFIAN AND MlJLLERIAN DUCTS BY THE LONGITUDINAL SPLITTING OF THE SEGMENTAL DUCT.

me. medullary canal; mp. muscle-plate; ch. notochord; ao. aorta; cav. cardinal vein; st. segmental tube. On the left side the section passes through the opening of a segmental tube into the body cavity. On the right this opening is represented by dotted lines, and the opening of the segmental tube into the Wolffian duct has been cut through; iv.d. Wolffian duct; m.d. Miillerian duct. The section is taken through the point where the segmental duct and Wolffian duct have just become separate; gr. the germinal ridge with the thickened germinal epithelium ; /. liver ; i. intestine with spiral valve.

and in the column of cells with which it is continuous being from the first incomplete.

The segmental tubes of the mesonephros undergo further important changes. The vesicle at the termination of each peritoneal funnel sends a bud forwards towards the preceding tubulus, which joins the fourth section of it close to the opening


EXCRETORY ORGANS.


695



into the Wolffian duct (fig. 390, px). The remainder of the vesicle becomes converted into a Malpighian body (mg}.

By the first of these changes 10^-4 M @W>f a tube is established connecting each pair of segments of the mesonephros, and though this tube is in part aborted (or only represented by a fibrous band) in the anterior part of the excretory organs in the adult, and most probably in the hinder part, yet it seems almost certain that the secondary and tertiary Malpighian bodies of the majority of segments are developed from its persisting blind end. Each of these


FIG. 390. LONGITUDINAL VERTICAL SECTION THROUGH PART OF THE MESONEPHROS OF AN EMBRYO OF SCYLLIUM.

The figure contains two examples of the budding of the vesicle of a segmental tube (which forms a Malpighian body in its own segment) to unite with the tubulus in the preceding segment close to its opening into the Wolffian (mesonephric) duct.

ge. epithelium of body-cavity; st. peritoneal funnel of segmental tube with its peritoneal opening; mg. Malpighian body; px. bud from Malphigian body uniting with preceding segment.


secondary and tertiary Malpighian bodies is connected with a convoluted tubulus (fig. 391, a.mg), which is also developed from the tube connecting each pair of segmental tubes, and therefore falls into the primary tubulus close to its junction with the


st.c



w.d


FIG. 391. THREE SEGMENTS OF THE ANTERIOR PART OF THE MESONEPHROS OF A NEARLY RIPE EMBRYO OF SCYLLIUM CANICULA AS A TRANSPARENT OBJECT. The figure shews a fibrous band passing from the primary to the secondary Malpighian bodies in two segments, which is the remains of the outgrowth from the primary Malpighian body.

sf.o. peritoneal funnel; p. ing. primary Malpighian body; a.mg. accessory Malpighian body; w.d. mesonephric (Wolffian) duct.


696 ELASMOBRANCI1II.


segmental duct. Owing to the formation of the accessory tubuli the segments of the mesonephros acquire a compound character.

The third section of each tubulus becomes by continuous growth, especially in the hinder segments, very bulky and convoluted.

The general character of a slightly developed segment of the mesonephros at its full growth may be gathered from fig. 391. It commences with (i) a peritoneal opening, somewhat oval in form (st.d) and leading directly into (2) a narrow tube, the segmental tube, which takes a more or less oblique course backwards, and, passing superficially to the Wolffian duct (w.d}, opens into (3) a Malpighian body (p.mg) at the anterior extremity of an isolated coil of glandular tubuli. This coil forms the third section of each segment, and starts from the Malpighian body. It consists of a considerable number of rather definite convolutions, and after uniting with tubuli from one, two, or more (according to the size of the segment) accessory Malpighian bodies (a.mg) smaller than the one into which the segmental tube falls, eventually opens by (4) a narrowish collecting tube into the Wolffian duct at the posterior end of the segment. Each segment is probably completely isolated from the adjoining segments, and never has more than one peritoneal funnel and one communication with the Wolffian duct.

Up to this time there has been no distinction between the anterior and posterior tubuli of the mesonephros, which alike open into the Wolffian duct. The collecting tubes of a considerable number of the hindermost tubuli (ten or eleven in Scyllium canicula), either in some species elongate, overlap, while at the same time their openings travel backward so that they eventually open by apertures (not usually so numerous as the separate tubes), on nearly the same level, into the hindermost section of the Wolffian duct in the female, or into the urinogenital cloaca, formed by the coalesced terminal parts of the Wolffian ducts, in the male; or in other species become modified, by a peculiar process of splitting from the Wolnian duct, so as to pour their secretion into a single duct on each side, which opens in a position corresponding with the numerous ducts of the other species (fig. 392). In both cases the modified posterior kidney-segments are probably equivalent to the per


EXCRETORY ORGANS. 697


manent kidney or metanephros of the amniotic Vertebrates, and for this reason the numerous collecting tubes or single collecting tube, as the case may be, will be spoken of as ureters. The anterior tubuli of the primitive excretory organ retain their early relation to the Wolffian duct, and form the permanent Wolffian body or mesonephros.

The originally separate terminal extremities of the Wolffian ducts always coalesce, and form a urinal cloaca, opening by a single aperture, situated at the extremity of the median papilla behind the anus. Some of the peritoneal openings of the segmental tubes in Scyllium, or in other cases all the openings, become obliterated.

In the male the anterior segmental tubes undergo remarkable modifications, and become connected with the testes. Branches appear to grow from the first three or four or more of them (though probably not from their peritoneal openings), which pass to the base of the testis, and there uniting into a longitudinal canal, form a network, and receive the secretion of the testicular ampullae (fig. 393, nf). These ducts, the vasa efferent ia, carry the semen to the Wolffian body, but before opening into the tubuli of this body they unite into a canal known as the longitudinal canal of the Wolffian body (l.c\ from which pass off ducts equal in number to the vasa efferentia, each of which normally ends in a Malpighian corpuscle. From the Malpighian corpuscles so connected there spring the convoluted tubuli, forming the generative segments of the Wolffian body, along which the semen is conveyed to the Wolffian duct (v.d). The Wolffian duct itself becomes much contorted and acts as vas deferens.

Figs. 392 and 393 are diagrammatic representations of the chief constituents of the adult urinogenital organs in the two sexes. In the adult female (fig. 392), there are present the following parts :

(1) The oviduct or Mullerian duct (m.d) split off from the segmental duct of the kidneys. Each oviduct opens at its anterior extremity into the body cavity, and behind the two oviducts have independent communications with the general cloaca.

(2) The mesonephric ducts (w.d), the other product of the


698


ELASMOBRANCHII.


segmental ducts of the kidneys. They end in front by becoming continuous with the tubulus of the anterior persisting segment of the mesonephros on each side, and unite behind to



FIG. 392. DIAGRAM OF THE ARRANGEMENT OF THE URINOGENITAL ORGANS

IN AN ADULT FEMALE ELASMOBRANCH.

m.d. Miillerian duct; w.d. Wolffian duct; s.t. segmental tubes; five of them are represented with openings into the body cavity, the posterior segmental tubes form the mesonephros ; ov. ovary.

open by a common papilla into the cloaca. The mesonephric duct receives the secretion of the anterior tubuli of the primitive mesonephros.

(3) The ureter which carries off the secretion of the kidney proper or metanephros. It is represented in my diagram in its most rare and differentiated condition as a single duct connected with the posterior segmental tubes.

(4) The segmental tubes (.$-./) some of which retain their


-S.t:



FIG. 393. DIAGRAM OF THE ARRANGEMENT OF THE URINOGENITAL ORGANS

IN AN ADULT MALE ELASMOBRANCH.

m.d. rudiment of Miillerian duct; w.d. Wolffian duct, marked vd in front and serving as vas deferens; s.t. segmental tubes; two of them are represented with openings into the body cavity; d. ureter; /. testis; nt. canal at the base of the testis; VE, vasa efferentia; Ic. longitudinal canal of the Wolffian body.


EXCRETORY ORGANS. 699


original openings into the body cavity, and others are without them. They are divided into two groups, an anterior forming the mesonephros or Wolffian body, which pours its secretion into the Wolffian duct ; and a posterior group forming a gland which is probably equivalent to the kidney proper of amniotic Craniata, and is connected with the ureter.

In the male the following parts are present (fig. 393):

(1) The Mlillerian duct (m.d], consisting of a small rudiment attached to the liver, representing the foremost end of the oviduct of the female.

(2) The mesonephric duct (w.d] which precisely corresponds to the mesonephric duct of the female, but, in addition to serving as the duct of the Wolffian body, also acts as a vas deferens (vd}. In the adult male its foremost part has a very tortuous course.

(3) The ureter (d\ which has the same fundamental constitution as in the female.

(4) The segmental tubes (s.t). The posterior tubes have the same arrangement in both sexes, but in the male modifications take place in connection with the anterior tubes to fit them to act as transporters of the semen.

Connected with the anterior tubes there are present (i) the vasa efferentia (VE], united on the one hand with (2) the central canal in the base of the testis (/), and on the other with the longitudinal canal of the Wolffian body (/<?). From the latter are seen passing off the successive tubuli of the anterior segments of the Wolffian body, in connection with which Malpighian bodies are typically present, though not represented in my diagram.

Apart from the absence of the pronephros the points which deserve notice in the Elasmobranch excretory system are (i) The splitting of the segmental duct into Wolffian (mesonephric) and Mullerian ducts. (2) The connection of the former with the mesonephros, and of the latter with the abdominal opening of the segmental duct which represents the pronephros of other types. (3) The fact that the Mullerian duct serves as oviduct, and the Wolffian duct as vas deferens. (4) The differentiation of a posterior section of the mesonephros into a special gland foreshadowing the metanephros of the Amniota.


/OO CYCLOSTOMATA.


Cyclostomata. The development of the excretory system amongst the Cyclostomata has only been studied in Petromyzon (Miiller, Furbringer, and Scott).

The first part of the system developed is the segmental duct. It appears in the embryo of about 14 days (Scott) as a solid cord of cells, differentiated from the somatic mesoblast near the dorsal end of the body cavity. This cord is at first placed immediately below the epiblast, and grows backwards by a continuous process of differentiation of fresh mesoblast cells. It soon acquires a lumen, and joins the cloacal section of the alimentary tract before the close of foetal life. Before this communication is established, the front end of the duct sends a process towards the body cavity, the blind end of which acquires a ciliated opening into the latter. A series of about four or five successively formed outgrowths from the duct, one behind the other, give rise to as many ciliated funnels opening into the body cavity, and each communicating by a more or less elongated tube with the segmental duct. These funnels, which have a metameric arrangement, constitute the pronephros, the whole of which is situated in the pericardial region of the body cavity.

On the inner side of the peritoneal openings of each pronephros there is formed a vascular glomerulus, projecting into the body cavity, and covered by peritoneal epithelium. For a considerable period the pronephros constitutes the sole functional part of the excretory system.

A mesonephros is formed (Furbringer) relatively late in larval life, as a segmentally arranged series of solid cords, derived from the peritoneal epithelium. These cords constitute the rudiments of the segmental tubes. They are present for a considerable portion of the body cavity, extending backwards from a point shortly behind the pronephros. They soon separate from the peritoneal epithelium, become hollowed out into canals, and join the segmental duct. At their blind extremity (that originally connected with the peritoneal epithelium) a Malpighian body is formed.

The pronephros is only a provisional excretory organ, the atrophy of which commences during larval life, and is nearly completed when the Ammoccete has reached 180 mm. in length.


EXCRETORY ORGANS. 70 1

Further changes take place in connection with the excretory system on the conversion of the Ammoccete into the adult.

The segmental ducts in the adult fall into a common urinogenital cloaca, which opens on a papilla behind the anus. This cloaca also communicates by two apertures (abdominal pores) with the body cavity. The generative products are carried into the cloaca by these pores ; so that their transportation outwards is not performed by any part of the primitive urinary system. The urinogenital cloaca is formed by the separation of the portion of the primitive cloaca containing the openings of the segmental ducts from that connected with the alimentary tract.

The mesonephros of the Ammoccete undergoes at the metamorphosis complete atrophy, and is physiologically replaced by a posterior series of segmental tubes, opening into the hindermost portion of the segmental duct (Schneider).

In Myxine the excretory system consists (i) of a highly developed pronephros with a bunch of ciliated peritoneal funnels opening into the pericardial section of the body cavity. The coiled and branched tubes of which the pronephros is composed open on the ventral side of the anterior portion of the segmental duct, which in old individuals is cut off from the posterior section of the duct. On the dorsal side of the portion of the segmental duct belonging to the pronephros there are present a small number of diverticula, terminating in glomeruli : they are probably to be regarded as anterior segmental tubes. (2) Of a mesonephros, which commences a considerable distance behind the pronephros, and is formed of straight extremely simple segmental tubes opening into the segmental duct (fig. 385).

The excretory system of Myxine clearly retains the characters of the system as it exists in the larva of Petromyzon.

Teleostei. In most Teleostei the pronephros and mesonephros coexist through life, and their products are carried off by a duct, the nature of which is somewhat doubtful, but which is probably homologous with the mesonephric duct of other types.

The system commences in the embryo (Rosenberg, Oellacher, Gotte, Furbringer) with the formation of a groove-like fold of the somatic layer of peritoneal epithelium, which becomes gradually constricted into a canal; the process of constriction commencing in the middle and extending in both directions. The canal does not however close anteriorly, but remains open to the body cavity, thus giving rise to a funnel equivalent to the pronephric funnels of Petromyzon and Myxine. On the inner side of this


702


TELEOSTEI.


funnel there is formed a glomerulus, projecting into the body

cavity ; and at the same time that

this is being formed the anterior end

of the canal becomes elongated and

convoluted. The above structures

constitute a pronephros, while the

posterior part of the primitive canal

forms the segmental duct.

The portion of the body cavity with the glomerulus and peritoneal funnel of the pronephros (fig. 395, po) soon becomes completely isolated from the remainder, so as to form a closed cavity (gl). The development of the mesonephros does not take place till long after that of the pronephros. The segmental tubes which form it are stated by Fiirbringer to arise from solid ingrowths of peritoneal epithelium, developed successively from before backwards, but Sedgwick informs me that they arise as differentiations of the mesoblastic cells near the peritoneal epithelium. They soon become hollow, and unite with the segmental duct. Malpighian bodies are developed on their median portions. They grow very greatly in length, and become much convoluted, but the details of this process have not been followed out.

The foremost segmental tubes are situated close behind the pronephros, while the hindermost are in many cases developed in the post-anal continuations of the body cavity. The pronephros appears to form the swollen cephalic portion of the kidney of the adult, and the mesonephros the remainder ; the so-called caudal portion, where present, being derived (?) from the postanal segmental tubes.

In some cases the cephalic portion of the kidneys is absent



FIG. 394. PORTIONS OF THE MESONEPHROS OF MYXINE. (From Gegenbaur; after J. Miiller.)

a. segmental duct ; b. segmental tube; c. glomerulus ; d. afferent, e. efferent artery.

B represents a portion of A highly magnified.


EXCRETORY ORGANS. 703


in the adult, which probably implies the atrophy of the pronephros ; in other instances the cephalic portion of the kidneys is the only part developed. Its relation to the embryonic proncphros requires however further elucidation.

In the adult the ducts in the lower part of the kidneys lie as a rule on their outer borders, and almost invariably open into a



pr


FIG. 395. SECTION THROUGH THE PRONEPHROS OF A TROUT AND ADJACENT PARTS TEN DAYS BEFORE HATCHING.

pr.n. pronephros ; po. opening of pronephros into the isolated portion of the body cavity containing the glomerulus ; gl. glomerulus ; ao. aorta ; ch. notochord ; x. subnotochordal rod ; al. alimentary tract.

urinary bladder, which usually opens in its turn on the urinogenital papilla immediately behind the genital pore, but in a few instances there is a common urinogenital pore.

In most Osseous Fish there are true generative ducts continuous with the investment of the generative organs. It appears to me most probable, from the analogy of Lepidostcus, to be described in the next section, that these ducts are split off from the primitive segmental duct, and correspond with the Miillerian ducts of Elasmobranchii, etc. ; though on this point we have at present no positive embryological evidence (vide general considerations at the end of the Chapter). In the female Salmon and the male and female Eel the generative products are carried to the exterior by abdominal pores. It is possible that this may represent a primitive condition, though it


704


GANOIDEI.


is more probably a case of degeneration, as is indicated by the presence of ducts in the male Salmon and in forms nearly allied to the Salmonidae.

The coexistence of abdominal pores and generative ducts in Mormyrus appears to me to demonstrate that the generative ducts in Teleostei cannot be derived from the coalescence of the investment of the generative organs with the abdominal pores.

Ganoidei. The true excretory gland of the adult Ganoidei resembles on the whole that of Teleostei, consisting of an elongated band on each side the mesonephros an anterior dilatation of which probably represents the pronephros.

There is in both sexes a Mullerian duct, provided, except in Lepidosteus, with an abdominal funnel, which is however situated relatively very far back in the abdominal cavity. The Mullerian ducts appear to serve as generative canals in both sexes. In Lepidosteus they are continuous with the investment of the generative glands, and thus a relation between the generative ducts and glands, very similar to that in Teleostei, is brought about.

Posteriorly the Mullerian ducts and the ducts of the mesonephros remain united. The common duct so formed on each side is clearly the primitive segmental duct. It receives the secretion of a certain number of the posterior mesonephric tubules, and usually unites with its fellow to form a kind of bladder, opening by a single pore into the cloaca, behind the anus. The duct which receives the secretion of the anterior mesonephric tubules is the true mesonephric or Wolffian duct.

The development of the excretory system, which has been partially worked out in Acipenscr and Lepidosteus 1 , is on the whole very similar to that in the Teleostei. The first portion of the system to



FIG. 396. SECTION THROUGH THE TRUNK OF A LEPIDOSTEUS EMBRYO ON THE SIXTH DAY AFTER IMPREGNATION.

me. medullary cord ; ms. mesoblast ; sg. segmental duct ; ch. notochord ; .r. subnotochordal rod; hy. hypoblast.


1 Acipenser has been investigated by Fiirbringer, Salensky, Sedgwick, and also by myself, and Lepidosteus by W. N. Parker and myself.


EXCRETORY ORGANS.


705


be formed is the segmental duct. In Lepidosteus this duct is formed as a groove-like invagination of the somatic peritoneal epithelium, precisely as in Teleostei, and shortly afterwards forms a duct lying between the mesoblast and the epiblast (fig. 396, sg}. In Acipenser (Salensky) however it is formed as



FIG. 397. TRANSVERSE SECTION THROUGH THE ANTERIOR PART OF AN ACIPENSER

EMBRYO. (After Salensky.)

Rf. medullary groove ; Alp. medullary plate ; Wg. segmental duct ; Ch. notochord ; En. hypoblast ; Sgp. mesoblastic somite ; Sp. parietal part of mesoblastic plate.

a solid ridge of the somatic mesoblast, as in Petromyzon and Elasmobranchii (fig. 397, Wg).

In both forms the ducts unite behind with the cloaca, and a pronephros of the Teleostean type appears to be developed. This gland is provided with but one 1 peritoneal opening, which together with the glomerulus belonging to it becomes encapsuled in a special section of the body cavity. The opening of the pronephros of Acipenser into this cavity is shewn in fig. ^<^>,pr.n. At this early stage of Acipenser (larva of 5 mm.) I could find no glomerulus.

The mesonephros is formed some distance behind, and some time after the pronephros, both in Acipenser and Lepidosteus, so that in the larvae of both these genera the pronephros is for a considerable period the only excretory organ. In Lepidosteus especially the development of the mesonephros occurs very late.

The development of the mesonephros has not been worked out in Lepidosteus, but in Acipenser the anterior segmental tubes become first established as (I believe) solid cords of cells, attached at one extremity to the peritoneal epithelium on each

1 I have not fully proved this point, but have never found more than one opening.


B. III.


45


GANOIDEI.


side of the insertion of the mesentery, and extending upwards and outwards round the segmental duct 1 . The posterior segmental tubes arise later than the anterior, and (as far as can be determined from the sections in my possession) they are formed independently of the peritoneal epithelium, on the dorsal side of the segmental duct.

In later stages (larvae of 7 10 mm.) the anterior segmental tubes gradually lose their attachment to the peritoneal epithelium. The extremity near the peritoneal epithelium forms a Malpighian body, and the other end unites with the segmental duct. At a still later stage wide peritoneal funnels are es


sjy.c


mjo


pr.n



FIG. 398. TRANSVERSE SECTION THROUGH THE REGION OF THE STOMACH OF A

LARVA OF ACIPENSER 5 MM. IN LENGTH.

st. epithelium of stomach ; yk. yolk ; ch. notochord, below which is a subnotochordal rod; pr.n. pronephros ; ao. aorta; mf. muscle-plate formed of large cells, the outer parts of which are differentiated into contractile fibres ; sp.c. spinal cord ; b.c. body cavity.

tablished, for at any rate a considerable number of the tubes, leading from the body cavity to the Malpighian bodies. These

1 Whether the segmental tubes are formed as ingrowths of the peritoneal epithelium, or in situ, could not be determined.


EXCRETORY ORGANS. 707

funnels have been noticed by Furbringer, Salensky and myself, but their mode of development has not, so far as I know, been made out. The funnels appear to be no longer present in the adult. The development of the Mullerian ducts has not been worked out.

Dipnoi. The excretory system of the Dipnoi is only known in the adult, but though in some respects intermediate in character between that of the Ganoidei and Amphibia, it resembles that of the Ganoidei in the important feature of the Mullerian ducts serving as genital ducts in both sexes.

Amphibia. In Amphibia (Gotte, Furbringer) the development of the excretory system commences, as in Teleostei, by the formation of the segmental duct from a groove formed by a fold of the somatic layer of the peritoneal epithelium, near the dorsal border of the body cavity (fig. 399, u). The anterior end of the groove is placed immediately behind the branchial region. Its posterior part soon becomes converted into a canal by a constriction which commences a short way from the front end of the groove, and thence extends backwards. This canal at first ends blindly close to the cloaca, into which however it soon opens.

The anterior open part of the groove in front of the constriction (fig. 399, n] becomes differentiated into a longitudinal duct, which remains in open communication with the body cavity by two (many Urodela) three (many Anura) or four (Cceciliidae) canals. This constitutes the dorsal part of the pronephros. The ventral part of the gland is formed from the section of the duct immediately behind the longitudinal canal. This part grows in length, and, assuming an S-shaped curvature, becomes placed on the ventral side of the first formed part of the pronephros. By continuous growth in a limited space the convolutions of the canal of the pronephros become more numerous, and the complexity of the gland is further increased by the outgrowth of blindly ending diverticula.

At the root of the mesentery, opposite the peritoneal openings of the pronephros, a longitudinal fold, lined by peritoneal epithelium, and attached by a narrow band of tissue, makes its appearance. It soon becomes highly vascular, and constitutes a glomerulus homologous with that in Petromyzon and Teleostei.

452


AMPHIBIA.


a*'


The section of the body cavity which contains the openings of the pronephros and the glomerulus, becomes dilated, and then temporarily shut off from the remainder. At a later period it forms a special though not completely isolated compartment. For a long time the pronephros and its duct form the only excretory organs of larval Amphibia. Eventually however the formation of the mesonephros commences, and is followed by the atrophy of the pronephros. The mesonephros is composed, as in other types, of a series of segmental tubes, but these, except in Cceciliidae, no longer correspond in number with the myotomes, but are in all instances more numerous. Moreover, in the posterior part of the mesonephros in the Urodeles, and through the whole length of the gland in other types, secondary and tertiary segmental tubes are formed in addition to the primary tubes.



FIG. 399. TRANSVERSE SECTION THROUGH A VERY YOUNG TADPOLE OF BOMBINATOR AT THE LEVEL OF THE ANTERIOR END OF THE YOLK-SACK. (After

Gotte.)

a. fold of epiblast continuous with the dorsal fin; is", neural cord; m. lateral muscle; as 1 . outer layer of muscle-plate; s. lateral plate of mesoblast ; b. mesentery ; u. open end of the segmental duct, which forms the pronephros ; f. alimentary tract ; f. ventral diverticulum which becomes the liver; e. junction of yolk cells and hypoblast cells ; d. yolk cells.


The development of the mesonephros commences in Salamandra (Fiirbringer) with the formation of a series of solid cords, which in the anterior myotomes spring from the peritoneal epithelium on the inner side of the segmental duct, but posteriorly arise independently of this epithelium in the adjoining mesoblast. Sedgwick informs me that in the

Frog the segmental tubes are throughout developed in the mesoblast, independently of the peritoneal epithelium. These cords next become detached from the peritoneal epithelium (in so far as they are primitively united to it), and after first assuming a vesicular form, grow out into coiled tubes, with a median limb the blind end of which assists in forming a Malpighian body, and a lateral limb which comes in contact with and opens into the segmental duct, and an intermediate portion connecting the two. At the junction of the median with the intermediate portion, and therefore at the neck of the Malpighian body, a canal grows out in a ventral direction, which meets the


EXCRETORY ORGANS. 709

peritoneal epithelium, and then develops a funnel-shaped opening into the body cavity, which subsequently becomes ciliated. In this way the peritoneal funnels which are present in the adult are established.

The median and lateral sections of the segmental tubes become highly convoluted, and the separate tubes soon come into such close proximity that their primitive distinctness is lost.

The first fully developed segmental tube is formed in Salamandra maculata in about the sixth myotome behind the pronephros. But in the region between the two structures rudimentary segmental tubes are developed.

The number of primary segmental tubes in the separate myotomes of Salamandra is as follows :

In the 6th myotome (i.e. the first with a true

segmental tube) 12 segmental tubes

yth roth myotome 23

IIth ... 34

I2th 3 4 or 4 5

I3th y> 45

1 3th i6th 56

It thus appears that the segmental tubes are not only more numerous than the myotomes, but that the number in each myotome increases from before backwards. In the case of Salamandra there are formed in the region of the posterior (10 16) myotomes secondary, tertiary, etc. segmental tubes out of independent solid cords, which arise in the mesoblast dorsally to the tubes already established.

The secondary segmental tubes appear to develop out of these cords exactly in the same way as the primary ones, except that they do not join the segmental duct directly, but unite with the primary segmental tubes shortly before the junction of the latter with the segmental duct. In this way compound segmental tubes are established with a common collecting tube, but with numerous Malpighian bodies and ciliated peritoneal openings. The difference in the mode of origin of these compound tubes and of those in Elasmobranchii is very striking.

The later stages in the development of the segmental tubes have not been studied in the other Amphibian types.

In Cceciliidas the earliest stages are not known, but the tubes present in the adult (Spengel) a truly segmental arrangement, and in the young each of them is single, and provided with only a single peritoneal funnel. In the adult however many of the segmental organs become compound, and may have as many as twenty funnels, etc. Both simple and compound segmental tubes occur in all parts of the mesonephros, and are arranged in no definite order.

In the Anura (Spengel) all the segmental tubes are compound, and an enormous number of peritoneal funnels are present on the ventral surface, but it has not yet been definitely determined into what part of the segmental tubes they open.


710 AMPHIBIA.


Before dealing with the further changes of the Wolffian body it is necessary to return to the segmental duct, which, at the time when the pronephros is undergoing atrophy, becomes split into a dorsal Wolffian and ventral Mullerian duct. The process in Salamandra (Fiirbringer) has much the same character as in Elasmobranchii, the Mullerian duct being formed by the gradual separation, from before backwards, of a solid row of cells from the ventral side of the segmental duct, the remainder of the duct constituting the Wolffian duct. During the formation of the Mullerian duct its anterior part becomes hollow, and attaching itself in front to the peritoneal epithelium acquires an opening into the body cavity. The process of hollowing is continued backwards pari passu with the splitting of the segmental duct. In the female the process is continued till the Mullerian duct opens, close to the Wolffian duct, into the cloaca. In the male the duct usually ends blindly. It is important to notice that the abdominal opening of the Mullerian duct in the Amphibia (Salamandra) is a formation independent of the pronephros, and placed slightly behind it ; and that the undivided anterior part of the segmental duct (with the pronephros) is not, as in Elasmobranchii, united with the Mullerian duct, but remains connected with the Wolffian duct.

The development of the Mullerian duct has not been satisfactorily studied in other forms besides Salamandra. In Cceciliidae its abdominal opening is on a level with the anterior end of the Wolffian body. In other forms it is usually placed very far forwards, close to the root of the lungs (except in Proteus and Batrachoseps, where it is placed somewhat further back), and some distance in front of the Wolffian body.

The Mullerian duct is always well developed in the female, and serves as oviduct. In the male it does not (except possibly in Alytes) assist in the transportation of the genital products, and is always more or less rudimentary, and in Anura may be completely absent.

After the formation of the Mullerian duct, the Wolffian duct remains as the excretory channel for the Wolffian body, and, till the atrophy of the pronephros, for this gland also. Its anterior section, in front of the Wolffian body, undergoes a more or less complete atrophy.

The further changes of the excretory system concern (i) the junction in the male of the anterior part of the Wolffian body with the testis ; (2) certain changes in the collecting tubes of the


EXCRETORY ORGANS.


711


posterior part of the mesonephros. The first of these processes results in the division of the Wolffian body into a sexual and a non-sexual part, and in Salamandra and other Urodeles the division corresponds with the distribution of the simple and compound segmental tubes.

Since the development of the canals connecting the testes with the sexual part of the Wolffian body has not been in all points satisfactorily elucidated, it will be convenient to commence with a description of the adult arrangement of the parts (fig. 400 B). In most instances a non-segmental system of canals the vasa effcrentia (ve) coming from the testis, fall into a canal known as the longitudinal canal of the Wolffian body, from which there pass off transverse canals, which fall into, and are equal in number to, the primary Malpighian bodies of the sexual part of the gland. The spermatozoa, brought to the Malpighian bodies, are thence transported along the segmental tubes to the Wolffian duct, and so to the exterior. The system of canals connecting the testis with the Malpighian bodies is known as the testicular network. The number of segmental tubes connected with the testis varies very greatly. In Siredon there are as many as from 30 32 (Spengel).

The longitudinal canal of the Wolffian body is in rare instances (Spelerpes, etc.) absent, where the sexual part of the Wolffian body is slightly developed. In the Urodela the testes are united with the anterior part of the Wolffian body. In the Cceciliidas the junction takes place in an homologous part of the Wolffian body, but, owing to the development of the anterior segmental tubes, which are rudimentary in the Urodela, it is situated some way behind the front end. Amongst the Anura the connection of the testis with the tubules of the Wolffian body is subject to considerable variations. In Bufo cinereus the normal Urodele type is preserved, and in Bombinator the same arrangement is found in a rudimentary condition, in that there are transverse trunks from the longitudinal canal of the Wolffian body, which end blindly, while the semen is carried into the Wolffian duct by canals in front of the Wolffian body. In Alytes and Discoglossus the semen is carried away by a similar direct continuation of the longitudinal canal in front of the Wolffian body, but there are no rudimentary transverse canals passing into the Wolffian body, as in Bombinator. In Rana the transverse ducts which pass off from the longitudinal canal of the Wolffian body, after dilating to form (?) rudimentary Malpighian bodies, enter directly into the collecting tubes near their opening into the Wolffian duct.


712 AMPHIBIA.


In most Urodeles the peritoneal openings connected with the primary generative Malpighian bodies atrophy, but in Spelerpes they persist. In the Cceciliidie they also remain in the adult state.

With reference to the development of these parts little is known except that the testicular network grows out from the primary Malpighian bodies, and becomes united with the testis. Embryological evidence, as well as the fact of the persistence of the peritoneal funnels of the generative region in the adults of some forms, proves that the testicular network is not developed from the peritoneal funnels.

Rudiments of the testicular network are found in the female Cceciliidae and in the females of many Urodela (Salamandra, Triton). These rudiments may in their fullest development consist of a longitudinal canal and of transverse canals passing from this to the Malpighian bodies, together with some branches passing into the mesovarium.

Amongst the Urodela the collecting tubes of the hinder non-sexual part of the Wolffian body, which probably represents a rudimentary metanephros, undergo in the male sex a change similar to that which they usually undergo in Elasmobranchii. Their points of junction with the Wolffian duct are carried back to the hindermost end of the duct (fig. 400 B), and the collecting tubes themselves unite together into one or more short ducts (ureters) before joining the Wolffian duct.

In Batrachoseps only the first collecting tube becomes split off in this way ; and it forms a single elongated ureter which receives all the collecting tubes of the posterior segmental tubes. In the female and in the male of Proteus, Menobranchus, and Siren the collecting tubes retain their primitive transverse course and open laterally into the Wolffian duct. In rare cases (Ellipsoglossus, Spengel} the ureters open directly into the cloaca.

The urinary bladder of the Amphibia is an outgrowth of the ventral wall of the cloacal section of the alimentary tract, and is homologous with the allantois of the amniotic Vertebrata.

The subjoined diagram (fig. 400) of the urogenital system of Triton illustrates the more important points of the preceding description.

In the female (A) the following parts are present :

(1) The Mullerian duct or oviduct (od) derived from the splitting of the segmental duct.

(2) The Wolffian duct (sug) constituting the portion of the segmental duct left after the formation of the Mullerian duct.

(3) The mesonephros (r), divided into an anterior sexual part


EXCRETORY ORGANS.


7'3


connected with a rudimentary testicular network, and a posterior part. The collecting tubes from both parts fall transversely into the Wolffian duct.

(4) The ovary (ov).

(5) The rudimentary testicular network.

In the male (B) the following parts are present :

(1) The functionless though fairly developed Miillerian duct (;).

(2) The Wolffian duct (sug).

(3) The mesonephros (r) divided into a true sexual part, through the segmental tubes of which the semen passes, and a non-sexual part. The collecting tubes of the latter do not enter the Wolffian duct directly, but bend obliquely backwards and only fall into it close to its cloacal aperture, after uniting to form one or two primary tubes (ureters).

(4) The testicular network (ve) consisting of (i) transverse ducts from the testes, falling into (2) the longitudinal canal of the Wolffian body, from which (3) transverse canals are again given off to the Malpighian bodies.

Amniota. The amniotic Vertebrata agree, so far as is known, very closely amongst themselves in the formation of the urinogenital system.

The most characteristic feature of the system is the full development of a metanephros, which constitutes the functional kidney on the atrophy of the mesonephros or Wolffian body, which is a purely embryonic organ. The first part of the system to develop is a duct, which is usually spoken of as the Wolffian duct, but which is really the homologue of the seg


FIG. 400. DIAGRAM OF THE URINOGENITAL SYSTEM OF TRITON. (From Gegenbaur ; after Spengel.)

A. Female. B. Male. r. mesonephros, on the surface of which numerous peritoneal funnels are visible ; sug. mesonephric or Wolffian duct; od. oviduct (Miillerian duct); in. Miillerian duct of male ; ve. vasa efferentia of testis ; t. testis ; ov. ovary ; up. urinogenital pore.


714 AMNIOTA.


mental duct. It apparently develops in all the Amniota nearly on the Elasmobranch type, as a solid rod, primarily derived from the somatic mesoblast of the intermediate cell mass (fig. 401 W.d}\

The first trace of it is visible in an embryo Chick with eight somites, as a ridge projecting from the intermediate cell mass towards the epiblast in the region of the seventh somite. In the course of further development it continues to constitute such a ridge as far as the eleventh somite (Sedgwick), but from this point it grows backwards in the space between the epiblast and mesoblast In an embryo with fourteen somites a small lumen has appeared in its middle part and in front it is connected with rudimentary Wolffian tubules, which develop in continuity with it (Sedgwick). In the succeeding stages the lumen of the duct gradually extends backwards and forwards, and the duct itself also passes inwards relatively to the epiblast (fig. 402). Its hindend elongates till it comes into connection with, and opens into, the cloacal section of the hind-gut' 2 .

It might have been anticipated that, as in the lower types, the anterior end of the segmental duct would either open into the body cavity, or come into connection with a pronephros. Neither of these occurrences takes place, though in some types (the Fowl) a structure, which is probably the rudiment of a pronephros, is developed ; it does not however appear till a later stage, and is then unconnected with the segmental duct. The next part of the system to appear is the mesonephros or Wolffian body.

This is formed in all Amniota as a series of segmental tubes, which in Lacertilia (Braun) correspond with the myotomes, but in Birds and Mammalia are more numerous.

In Reptilia (Braun, No. 542), the mesonephric tubes develop as segmentally-arranged masses on the inner side of the Wolffian duct, and appear to be at first united with the peritoneal epithelium. Each mass soon becomes an oval vesicle, probably opening for a very short period into the

1 Dansky and Kostenitsch (No. 543) describe the Wolffian duct in the Chick as developing from a groove opening to the peritoneal cavity, which subsequently becomes constricted into a duct. I have never met with specimens such as those figured by these authors.

2 The foremost extremity of the segmental duct presents, according to Gasser, curious irregularities and an anterior completely isolated portion is often present.


EXCRETORY ORGANS.


715


peritoneal cavity by a peritoneal funnel. The vesicles become very early detached from the peritoneal epithelium, and lateral outgrowths from them give rise to the main parts of the segmental tubes, which soon unite with the segmental duct.

In Birds the development of the segmental tubes is more complicated 1 .

The tubules of the Wolffian body are derived from the intermediate cell mass, shewn in fig. 401, between the upper end of the body cavity and the


g.o.



FIG. 401. TRANSVERSE SECTION THROUGH THE DORSAL REGION OF AN

EMBRYO CHICK OF 45 HOURS.

M.c. medullary canal ; P.v. mesoblastic somite ; W.d. Wolffian duct which is in contact with the intermediate cell mass ; So. somatopleure ; S.p. splanchnopleure ; p.p. pleuroperitoneal cavity ; ch. notochord ; op. boundary of area opaca; v. bloodvessel.

muscle-plate. In the Chick the mode of development of this mass into the segmental tubules is different in the regions in front of and behind about the sixteenth segment. In front of about the sixteenth segment the intermediate cell mass becomes detached from the peritoneal epithelium at certain points, remaining attached to it at other points, there being several such to each segment. The parts of the intermediate cell mass attached to the peritoneal epithelium become converted into S-shaped cords (fig. 402, st] which soon unite with the segmental duct (wd}. Into the commencement of each of these cords the lumen of the body cavity is for a short distance prolonged, so that this part constitutes a rudimentary peritoneal funnel.

1 Correct figures of the early stages of these structures were first given by Kolliker, but the correct interpretation of them and the first satisfactory account of the development of the excretory organs of Birds was given by Sedgwick (No. 549).


716


AMNIOTA.


In the Duck the attachment of the intermediate cell mass to the peritoneal epithelium is prolonged further back than in the Chick.

In the foremost segmental tubes, which never reach a very complete development, the peritoneal funnels widen considerably, while at the same time they acquire a distinct lumen. The section of the tube adjoining the wide peritoneal funnel becomes partially invaginated by the formation of a glomerulus, and this glomerulus soon grows to such an extent as to project through the peritoneal funnel, the neck of which it completely fills, into the body cavity (fig. 403, gl). There is thus formed a series of free peritoneal glomeruli belonging to the anterior Wolfnan tubuli 1 . These tubuli become however early aborted.

In the case of the remaining tubules developed from the S-shaped cords the attachment to the peritoneal epithelium is very soon lost. The cords acquire a lumen, and open into the segmental duct. Their blind extremities constitute the rudiments of Malpighian bodies.


am



FIG. 402. TRANSVERSE SECTION THROUGH THE TRUNK OF A DUCK EMBRYO WITH

ABOUT TWENTY-FOUR MESOBLASTIC SOMITES.

am. amnion ; so. somatopleure ; sp. splanchnopleure ; ivd. Wolffian duct ; st. segmental tube; ca.v. cardinal vein; m.s. muscle-plate; sp.g. spinal ganglion; sp.c. spinal cord ; ch. notochord ; ao. aorta ; hy. hypoblast.

1 These external glomeruli were originally mistaken by me (No. 539) for the glomeralus of the pronephros, from their resemblance to the glomerulus of the Amphibian pronephros. Their true meaning was made out by Sedgwick (No. 550).


EXCRETORY ORGANS.


717


In the posterior part of the Wolffian body of the Chick the intermediate cell mass becomes very early detached from the peritoneal epithelium, and at a considerably later period breaks up into oval vesicles similar to those of the Reptilia, which form the rudiments of the segmental tubes.

Secondary and tertiary segmental tubules are formed in the Chick, on the dorsal side of the primary tubules, as direct differentiations of the mesoblast. They open independently into the Wolffian duct.

In Mammalia the segmental tubules (Egli) are formed as solid masses in the same situation as in Birds and Reptiles. It is not known whether they are united with the peritoneal epithelium. They soon become oval vesicles, which develop into complete tubules in the manner already indicated.



After the establishment of the Wolffian body there is formed in both sexes in all the Amniota a duct, which in the female becomes the oviduct, but which is functionless and disappears more or less completely in the male. This duct, in spite of certain peculiarities in its development, is without doubt homologous with the Mullerian duct of


FIG. 403. SECTION THROUGH THE EXTERNAL GLOMERULUS OF ONE OF THE ANTERIOR SEGMENTAL TUBES OF AN EMBRYO CHICK OF ABOUT IOO H.

gl. glomerulus ; ge. peritoneal epithelium ; Wd. Wolffian duct ; ao. aorta ; me. mesentery. The segmental tube, and the connection between the external and internal parts of the glomerulus are not shewn in this figure.



FIG. 404. SECTIONS SHEWING TWO OF THE PERITONEAL INVAGINATIONS WHICH GIVE RISE TO THE ANTERIOR PART OF THE MULLERIAN DUCT (PRONEPHROS). (After Balfour and Sedgwick. )

A is the nth section of the series. B i 5th

C i8th ,, ,,

gri. second groove ; gr$. third groove ; ri. second ridge ; wit. Wolffian duct.


7 i8


AMNIOTA.


the Ichthyopsida. In connection with its anterior extremity certain structures have been found in the Fowl, which are probably, on grounds to be hereafter stated, homologous with the pronephros (Balfour and Sedgwick).

The pronephros, as I shall call it, consists of a slightly convoluted longitudinal canal with three or more peritoneal openings. In the earliest condition, it consists of three successive open involutions of the peritoneal epithelium, connected together by more or less well-defined ridge-like thickenings of the epithelium. It takes its origin from the layer of thickened peritoneal epithelium situated near the dorsal angle of the body cavity, and is situated some considerable distance behind the front end of the Wolfifian duct.

In a slightly later stage the ridges connecting the grooves become partially constricted off from the peritoneal epithelium,



FIG. 405. SECTION OF THE WOLFFIAN BODY DEVELOPING PRONEPHROS AND GENITAL GLAND OF THE FOURTH DAY. (After Waldeyer.) Magnified 160 times. m. mesentery; Z. somatopleure ; a', portion of the germinal epithelium from which the involution (2) to form the pronephros (anterior part of Miillerian duct) takes place; a. thickened portion of the germinal epithelium in which the primitive germinal cells C and o are lying ; E. modified mesoblast which will form the stroma of the ovary ; WK. Wolffian body ; y. Wolffian duct.


EXCRETORY ORGANS. 719

and develop a lumen. The condition of the structure at this stage is illustrated by fig. 404, representing three transverse sections through two grooves, and through the ridge connecting them.

The pronephros may in fact now be described as a slightly convoluted duct, opening into the body cavity by three groovelike apertures, and continuous behind with the rudiment of the true Miillerian duct.

The stage just described is that of the fullest development of the pronephros. In it, as in all the previous stages, there appear to be only three main openings into the body cavity ; but in some sections there are indications of the possible presence of one or two additional rudimentary grooves.

In an embryo not very much older than the one last described the pronephros atrophies as such, its two posterior openings vanishing, and its anterior opening remaining as the permanent opening of the Miillerian duct.

The pronephros is an extremely transitory structure, and its development and atrophy are completed between the QOth and i2Oth hours of incubation.

The position of the pronephros in relation to the Wolffian body is shewn in fig. 405, which probably passes through a region between two of the peritoneal openings. As long as the pronephros persists, the Mullerian duct consists merely of a very



FlG. 406. TWO SECTIONS SHEWING THE JUNCTION OF THE TERMINAL SOLID PORTION OF THE MtJLLERIAN DUCT WITH THE WOLFFIAN DUCT. (After Balfour

and Sedgwick.)

In A the terminal portion of the duct is quite distinct ; in B it has united with the walls of the Wolffian duct.

md. Mullerian duct ; Wd. Wolffian duct.


72O AMNIOTA.


small rudiment, continuous with the hindermost of the three peritoneal openings, and its solid extremity appears to unite with the walls of the Wolffian duct.

After the atrophy of the pronephros, the Miillerian duct commences to grow rapidly, and for the first part of its course it appears to be split off as a solid rod from the outer or ventral wall of the Wolffian duct (fig. 406). Into this rod the lumen, present in its front part, subsequently extends. Its mode of development in front is thus precisely similar to that of the Miillerian duct in Elasmobranchii and Amphibia.

This mode of development only occurs however in the anterior part of the duct. In the posterior part of its course its growing point lies in a bay formed by the outer walls of the Wolffian duct, but does not become definitely attached to that duct. It seems however possible that, although not actually split off from the walls of the Wolrfian duct, it may grow backwards from cells derived from that duct.

The Miillerian duct finally reaches the cloaca though it does not in the female for a long time open into it, and in the male never does so.

The mode of growth of the Miillerian duct in the posterior part of its course will best be understood from the following description quoted from the paper by Sedgwick and myself.

"A few sections before its termination the Miillerian duct appears as a well-defined oval duct lying in contact with the wall of the Wolffian duct on the one hand and the germinal epithelium on the other. Gradually, however, as we pass backwards, the Miillerian duct dilates ; the external wall of the Wolffian duct adjoining it becomes greatly thickened and pushed in in its middle part, so as almost to touch the opposite wall of the duct, and so form a bay in which the Miillerian duct lies. As soon as the Miillerian duct has come to lie in this bay its walls lose their previous distinctness of outline, and the cells composing them assume a curious vacuolated appearance. No well-defined line of separation can any longer be traced between the walls of the Wolffian duct and those of the Miillerian, but between the two is a narrow clear space traversed by an irregular network of fibres, in some of the meshes of which nuclei are present.

The Miillerian duct may be traced in this condition for a considerable number of sections, the peculiar features above described becoming more and more marked as its termination is approached. It continues to dilate and attains a maximum size in the section or so before it disappears. A lumen may be observed in it up to its very end, but is usually irregular in outline and frequently traversed by strands of protoplasm. The Miillerian


EXCRETORY ORGANS. 721

duct finally terminates quite suddenly, and in the section immediately behind its termination the Wolffian duct assumes its normal appearance, and the part of its outer wall on the level of the Miillerian duct conies into contact with the germinal epithelium."

Before describing the development of the Mullerian duct in other Amniotic types it will be well to say a few words as to the identifications above adopted. The identification of the duct, usually called the Wolffian duct, with the segmental duct (exclusive of the pronephros) appears to be morphologically justified for the following reasons : (i) that it gives rise to part of the Mullerian duct as well as to the duct of the Wolffian body ; behaving in this respect precisely as does the segmental duct of Elasmobranchii and Amphibia. (2) That it serves as the duct for the Wolffian body, before the Mullerian duct originates from it. (3) That it develops in a manner strikingly similar to that of the segmental duct of various lower forms.

With reference to the pronephros it is obvious that the organ identified as such is in many respects similar to the pronephros of the Amphibia. Both consist of a somewhat convoluted longitudinal canal, with a certain number of peritoneal openings ;

The main difficulties in the homology are :

(1) the fact that the pronephros in the Bird is not united with the segmental duct ;

(2) the fact that it is situated behind the front end of the Wolffian body. It is to be remembered in connection with the first of these difficulties

that in the formation of the Mullerian duct in Elasmobranchii the anterior undivided extremity of the primitive segmental duct, with the peritoneal opening, which probably represents the pronephros, is attached to the Mullerian duct, and not to the Wolffian duct ; though in Amphibia the reverse is the case. To explain the discontinuity of the pronephros with the segmental duct it is only necessary to suppose that the segmental duct and pronephros, which in the Ichthyopsida develop as a single formation, develop in the Bird as two independent structures a far from extravagant supposition, considering that the pronephros in the Bird is undoubtedly quite functionless.

With reference to the posterior position of the pronephros it is only necessary to remark that a change in position might easily take place after the acquirement of an independent development, and that the shifting is probably correlated with a shifting of the abdominal opening of the Mullerian duct.

The pronephros has only been observed in Birds, and is very possibly not developed in other Amniota. The Mullerian duct is also usually stated to develop as a groove of the peritoneal epithelium, shewn in the Lizard in fig. 354, md., which is continued backward as a primitively solid rod in the space between B. ill. 46


722


AM N IOTA.


the Wolffian duct and peritoneal epithelium, without becoming attached to the Wolffian duct.

On the formation of the Miillerian duct, the duct of the mesonephros becomes the true mesonephric or Wolffian duct.

After these changes have taken place a new organ of great importance makes its appearance. This organ is the permanent kidney, or metanephros.

Metanephros. The mode of development of the metanephros has as yet only been satisfactorily elucidated in the Chick (Sedgwick, No. 549). The ureter and the collecting tubes of the kidney are developed from a dorsal outgrowth of the hinder part of the Wolffian duct. The outgrowth from the Wolffian duct grows forwards, and extends along the outer side of a mass of mesoblastic tissue which lies mainly behind, but somewhat overlaps the dorsal aspect of the Wolffian body.

This mass of mesoblastic cells may be called the metanephric blastema. Sedgwick, of the accuracy of whose account I have satisfied myself, has shewn that in the Chick it is derived from the intermediate cell mass of the region of about the thirty-first to the thirty-fourth somite. It is at first continuous with, and indistinguishable in structure from, the portion of the intermediate cell mass of the region immediately in front of it, which breaks up into Wolffian tubules. The metanephric blastema remains however quite passive during the formation of the Wolffian tubules in the adjoining blastema ; and on the formation of the ureter breaks off from the Wolffian body in front, and, growing forwards and dorsalwards, places itself on the inner side of the ureter in the position just described.

In the subsequent development of the kidney collecting tubes grow out from the ureter, and become continuous with masses of cells of the metanephric blastema, which then differentiate themselves into the kidney tubules.

The process just described appears to me to prove that the kidney of the A mniota is a specially differentiated posterior section of the primitive mesonephros.

According to the view of Remak and Kolliker the outgrowths from the ureter give rise to the whole of the tubuli uriniferi and the capsules of the Malpighian bodies, the mesoblast around them forming blood-vessels, etc. On the other hand some observers (Kupffer, Bornhaupt, Braun) maintain, in


EXCRETORY ORGANS. 723


accordance with the account given above, that the outgrowths of the ureter form only the collecting tubes, and that the secreting tubuli, etc. are formed in situ in the adjacent mesoblast.

Braun (No. 542) has arrived at the conclusion that in the Lacertilia the tissue, out of which the tubuli of the metanephros are formed, is derived from irregular solid ingrowths of the peritoneal epithelium, in a region behind the Wolffian body, but in a position corresponding to that in which the segmental tubes take their origin. These ingrowths, after separating from the peritoneal epithelium, unite together to form a cord into which the ureter sends the lateral outgrowths already described. These outgrowths unite with secreting tubuli and Malpighian bodies, formed in situ. In Lacertilia the blastema of the kidney extends into a postanal region. Braun's account of the origin of the metanephric blastema does not appear to me to be satisfactorily demonstrated.

The ureter does not long remain attached to the Wolffian duct, but its opening is gradually carried back, till (in the Chick between the 6th and 8th day) it opens independently into the cloaca.

Of the further changes in the excretory system the most important is the atrophy of the greater part of the Wolffian body, and the conversion of the Wolffian duct in the male sex into the vas deferens, as in Amphibia and the Elasmobranchii.

The mode of connection of the testis with the Wolffian duct is very remarkable, but may be derived from the primitive arrangement characteristic of Elasmobranchii and Amphibia.

In the structures connecting the testis with the Wolffian body two parts have to be distinguished, (i) that equivalent to the testicular network of the lower types, (2) that derived from the segmental tubes. The former is probably to be found in peculiar outgrowths from the Malpighian bodies at the base of the testes.

These were first discovered by Braun in Reptilia, and consist in this group of a series of outgrowths from the primary (?) Malpighian bodies along the base of the testis : they unite to form an interrupted cord in the substance of the testis, from which the testicular tubuli (with the exception of the seminiferous cells) are subsequently differentiated. These outgrowths, with the exception of the first two or three, become detached from the Malpighian bodies. Outgrowths similar to those in the male are found in the female, but subsequently atrophy.

Outgrowths homologous with those found by Braun have

46 2


724 AMNIOTA.


been detected by myself (No. 555) in Mammals. It is not certain to what parts of the testicular tubuli they give rise, but they probably form at any rate the vasa recta and rete vasculosum.

In Mammals they also occur in the female, and give rise to cords of tissue in the ovary, which may persist through life.

The comparison of the tubuli, formed out of these structures, with the Elasmobranch and Amphibian testicular network is justified in that both originate as outgrowths from the primary Malpighian bodies, and thence extend into the testis, and come into connection with the true seminiferous stroma.

As in the lower types the semen is transported from the testicular network to the Wolffian duct by parts of the glandular tubes of the Wolffian body. In the case of Reptilia the anterior two or three segmental tubes in the region of the testis probably have this function. In the case of Mammalia the vasa efferentia, i.e. the coni vasculosi, appear, according to the usually accepted view, to be of this nature, though Banks and other investigators believe that they are independently developed structures. Further investigations on this point are required. In Birds a connection between the Wolffian body and the testis appears to be established as in the other types. The Wolffian duct itself becomes, in the males of all Amniota, the vas deferens and the convoluted canal of the epididymis the latter structure (except the head) being entirely derived from the Wolffian duct.

In the female the Wolffian duct atrophies more or less completely.

In Snakes (Braun) the posterior part remains as a functionless canal, commencing at the ovary, and opening into the cloaca. In the Gecko (Braun) it remains as a small canal joining the ureter ; in Blindworms a considerable part of the canal is left, and in Lacerta (Braun) only interrupted portions.

In Mammalia the middle part of the duct, known as Gaertner's canal, persists in the females of some monkeys, of the pig and of many ruminants.

The Wolffian body atrophies nearly completely in both sexes ; though, as described above, part of it opposite the testis persists as the head of the epididymis. The posterior part of the gland from the level of the testis may be called the sexual part of the gland, the anterior part forming the non-sexual part.


EXCRETORY ORGANS. 725

The latter, i.e. the anterior part, is first absorbed ; and in some Reptilia the posterior part, extending from the region of the genital glands to the permanent kidney, persists till into the second year.

Various remnants of the Wolffian body are found in the adults of both sexes in different types. The most constant of them is perhaps the part in the female equivalent to the head of the epididymis and to parts also of the coiled tube of the epididymis, which may be called, with Waldeyer, the epoophoron 1 . This is found in Reptiles, Birds and Mammals ; though in a very rudimentary form in the first-named group. Remnants of the anterior non-sexual part of the Wolffian bodies have been called by Waldeyer parepididymis in the male, and paroophoron in the female. Such remnants are not (Braun) found in Reptilia, but are stated to be found in both male and female Birds, as a small organ consisting of blindly ending tubes with yellow pigment. In some male Mammals (including Man) a parepididymis is found on the upper side of the testis. It is usually known as the organ of Giraldes.

The Mlillerian duct forms, as has been stated, the oviduct in the female. The two ducts originally open independently into the cloaca, but in the Mammalia a subsequent modification of this arrangement occurs, which is dealt with in a separate section. In Birds the right oviduct atrophies, a vestige being sometimes left. In the male the Miillerian ducts atrophy more or less completely.

In most Reptiles and in Birds the atrophy of the Miillerian ducts is complete in the male, but in Lacerta and Anguis a rudiment of the anterior part has been detected by Leydig as a convoluted canal. In the Rabbit (Kolliker) 2 and probably other Mammals the whole of the ducts probably disappears, but in some Mammals, e.g. Man, the lower fused ends of the Miillerian ducts give rise to a pocket opening into the urethra, known as the uterus masculinus ; and in other cases, e.g. the Beaver and the Ass, the rudiments are more considerable, and may be continued into horns homologous with the horns of the uterus (Weber).

The hydatid of Morgani in the male is supposed (Waldeyer) to represent the abdominal opening of the Fallopian tube in the female, and therefore to be a remnant of the Miillerian duct.

Changes in the lower parts of the urinogenital ducts in the Amniota.

The genital cord. In the Monodelphia the lower part of the Wolffian ducts becomes enveloped in both sexes in a special

1 This is also called parovarium (His), and Rosenmiiller's organ.

2 Weber (No. 553) states that a uterus masculinus is present in the Rabbit, but his account is by no means satisfactory, and its presence is distinctly denied by Kolliker.


726


AMNIOTA.


cord of tissue, known as -the genital cord (fig. 407, gc), within the lower part of which the MUllerian ducts are also enclosed. In the male the MUllerian ducts in this cord atrophy, except at their distal end where they unite to form the uterus masculinus. The Wolffian ducts, after becoming the vasa deferentia, remain for some time enclosed in the common cord, but afterwards separate from each other. The seminal vesicles are outgrowths of the vasa deferentia.

In the female the Wolffian ducts within the genital cord atrophy, though rudiments of them are for a long time visible or even permanently persistent. The lower parts of the MUllerian ducts unite to form the vagina and body of the uterus. The junction commences in the middle and extends forwards and backwards ; the stage with a median junction being retained permanently in Marsupials.

The urinogenital sinus and external generative organs. In all the Amniota, there open at first into the common cloaca the alimentary canal dorsally, the allantois ventrally, and the Wolffian and MUllerian ducts and ureters laterally. In Reptilia and Aves the embryonic condition is retained. In both groups the allantois serves as an embryonic urinary bladder, but while it atrophies in Aves, its stalk dilates to form a permanent urinary bladder in Reptilia. In Mammalia the dorsal part of the cloaca with the alimentary tract becomes first of all partially constricted off from the ventral, which then forms a urinogenital sinus (fig. 407, ug). In the course of development the urinogenital sinus becomes, in all Mammalia but the Ornithodelphia, completely separated from the intestinal cloaca, and the two parts obtain separate external openings. The ureters (fig. 407, 3) open higher up than the other ducts into the stalk of the allantois which dilates to form the bladder (4). The stalk connecting the bladder with the ventral wall of the body constitutes the urachus, and loses its lumen before the close of embryonic life. The part of the stalk of the allantois below the openings of the ureters narrows to form the urethra, which opens together with the Wolffian and MUllerian ducts into the urinogenital cloaca.

In front of the urinogenital cloaca there is formed a genital prominence (fig. 407, cp), with a groove continued from the


EXCRETORY ORGANS. 727

urinogenital opening ; and on each side a genital fold (&). In the male the sides of the groove on the prominence coalesce together, embracing between them the opening of the urinogenital cloaca ; and the prominence itself gives rise to the penis,



FIG. 407. DIAGRAM OF THE URINOGENITAL ORGANS OF A MAMMAL AT AN EARLY STAGE. (After Allen Thomson ; from Quain's Anatomy.)

The parts are seen chiefly in profile, but the Miillerian and Wolffian ducts are seen from the front.

3. ureter; 4. urinary bladder ; 5. urachus; of. genital ridge (ovary or testis) ; W. left Wolffian body ; x. part at apex from which coni vasculosi are afterwards developed ; w. Wolffian duct ; m. Miillerian duct ; gc. genital cord consisting of Wolffian and Mullerian ducts bound up in a common sheath ; i. rectum ; ug. urinogenital sinus ; cp. elevation which becomes the clitoris or penis ; Is. ridge from which the labia majora or scrotum are developed.

along which the common urinogenital passage is continued. The two genital folds unite from behind forwards to form the scrotum.

In the female the groove on the genital prominence gradually disappears, and the prominence remains as the clitoris, which is therefore the homologue of the penis : the two genital folds form the labia majora. The urethra and vagina open independently into the common urinogenital sinus.


728 GENERAL CONCLUSIONS.

General conclusions and Summary.

Pronephros. Sedgwick has pointed out that the pronephros is always present in types with a larval development, and either absent or imperfectly developed in those types which undergo the greater part of their development within the egg. Thus it is practically absent in the embryos of Elasmobranchii and the Amniota, but present in the larvae of all other forms.

This coincidence, on the principles already laid down in a previous chapter on larval forms, affords a strong presumption that the pronephros is an ancestral organ ; and, coupled with the fact that it is the first part of the excretory system to be developed, and often the sole excretory organ for a considerable period, points to the conclusion that the pronephros and its duct the segmental duct are the most primitive parts of the Vertebrate excretory system. This conclusion coincides with that arrived at by Gegenbaur and Fiirbringer.

The duct of the pronephros is always developed prior to the gland, and there are two types according to which its development may take place. It may either be formed by the closing in of a continuous groove of the somatic peritoneal epithelium (Amphibia, Teleostei, Lepidosteus), or as a solid knob or rod of cells derived from the somatic mesoblast, which grows backwards between the epiblast and the mesoblast (Petromyzon, Elasmobranchii, and the Amniota).

It is quite certain that the second of these processes is not a true record of the evolution of 'the duct, and though it is more possible that the process observable in Amphibia and the Teleostei may afford some indications of the manner in which the duct was established, this cannot be regarded as by any means certain.

The mode of development of the pronephros itself is apparently partly dependent on that of its duct. In Petromyzon, where the duct does not at first communicate with the body cavity, the pronephros is formed as a series of outgrowths from the duct, which meet the peritoneal epithelium and open into the body cavity ; but in other instances it is derived from the anterior open end of the groove which gives rise to the segmental duct. The open end of this groove may either remain single


EXCRETORY ORGANS. 729

(Teleostci, Ganoidei) or be divided into two, three or more apertures (Amphibia). The main part of the gland in either case is formed by convolutions of the tube connected with the peritoneal funnel or funnels. The peritoneal funnels of the pronephros appear to be segmentally arranged.

The pronephros is distinguished from the mesonephros by developmental as well as structural features. The most important of the former is the fact that the glandular tubules of which it is formed are always outgrowths of the segmental duct ; while in the mesonephros they are always or almost always 1 formed independently of the duct.

The chief structural peculiarity of the pronephros is the absence from it of Malpighian bodies with the same relations as those in the meso- and metanephros; unless the structures found in Myxine are to be regarded as such. Functionally the place of such Malpighian bodies is taken by the vascular peritoneal ridge spoken of in the previous pages as the glomerulus.

That this body is really related functionally to the pronephros appears to be indicated (i) by its constant occurrence with the pronephros and its position opposite the peritoneal openings of this body ; (2) by its atrophy at the same time as the pronephros ; (3) by its enclosure together with the pronephridian stoma in a special compartment of the body-cavity in Teleostei and Ganoids, and its partial enclosure in such a compartment in Amphibia.

The pronephros atrophies more or less completely in most types, though it probably persists for life in the Teleostei and Ganoids, and in some members of the former group it perhaps forms the sole adult organ of excretion.

The cause of its atrophy may perhaps be related to the fact that it is situated in the pericardial region of the body-cavity, the dorsal part of which is aborted on the formation of a closed pericardium ; and its preservation in Teleostei and Ganoids may on this view be due to the fact that in these types its peritoneal funnel and its glomerulus are early isolated in a special cavity.

Mesonephros. The mesonephros is in all instances composed of a series of tubules (segmental tubes) which are developed independently of the segmental duct. Each tubule is

1 According t.o Sedgwick some of the anterior segmental tubes of Aves form an exception to the general rule that there is no outgrowth from the segmental or metanephric duct to meet the segmental tubes.


730 GENERAL CONCLUSIONS.

typically formed of (i) a peritoneal funnel opening into (2) a Malpighian body, from which there proceeds (3) a coiled glandular tube, finally opening by (4) a collecting tube into the segmental duct, which constitutes the primitive duct for the mesonephros as well as for the pronephros.

The development of the mesonephridian tubules is subject to considerable variations.

(1) They may be formed as differentiations of the intermediate cell mass, and be from the first provided with a lumen, opening into the body-cavity, and directly derived from the section of the body-cavity present in the intermediate cell mass; the peritoneal funnels often persisting for life (Elasmobranchii).

(2) They may be formed as solid cords either attached to or independent of the peritoneal epithelium, which after first becoming independent of the peritoneal epithelium subsequently send downwards a process, which unites with it and forms a peritoneal funnel, which may or may not persist (Acipenser, Amphibia).

(3) They may be formed as in the last case, but acquire no secondary connection with the peritoneal epithelium (Teleostei, Amniota). In connection with the original attachment to the peritoneal epithelium, a true peritoneal funnel may however be developed (Aves, Lacertilia).

Physiological considerations appear to shew that of these three methods of development the first is the most primitive. The development of the tubes as solid cords can hardly be primary.

A question which has to be answered in reference to the segmental tubes is that of the homology of the secondarily developed peritoneal openings of Amphibia, with the primary openings of the Elasmobranchii. It is on the one hand difficult to understand why, if the openings are homologous in the two types, the original peritoneal attachment should be obliterated in Amphibia, only to be shortly afterwards reacquired. On the other hand it is still more difficult to understand what physiological gain there could be, on the assumption of the non-homology of the openings, in the replacement of the primary opening by a secondary opening exactly similar to it. Considering the great variations in development which occur in undoubtedly homologous parts I incline to the view that the openings in the two types are homologous.


EXCRETORY ORGANS.


731


In the majority of the lower Vertebrata the mesonephric tubes have at first a segmental arrangement, and this is no doubt the primitive condition. The coexistence of two, three, or more of them in a single segment in Amphibia, Aves and Mammalia has recently been shewn, by an interesting discovery of Eisig, to have a parallel amongst Chaetopods, in the coexistence of several segmental organs in a single segment in some of the Capitellidae.

In connection with the segmental features of the mesonephros it is perhaps worth recalling the fact that in Elasmobranchii as well as other types there are traces of segmental tubes in some of the postanal segments. In the case of all the segmental tubes a Malpighian body becomes established close to the extremity of the tube adjoining the peritoneal opening, or in an homologous position in tubes without such an opening. The opposite extremity of the tube always becomes attached to the segmental duct.

In many of the segments of the mesonephros, especially in the hinder ones, secondary and tertiary tubes become developed in certain types, which join the collecting canals of the primary tubes, and are provided, like the primary tubes, with Malpighian bodies at their blind extremities.

There can it appears to me be little or no doubt that the secondary tubes in the different types are homodynamous if not homologous. Under these circumstances it is surprising to find in what different ways they take their origin. In Elasmobranchii a bud sprouts out from the Malpighian body of one segment, and joins the collecting tube of the preceding segment, and subsequently, becoming detached from the Malpighian body from which it sprouted, forms a fresh secondary Malpighian body at its blind extremity. Thus the secondary tubes of one segment are formed as buds from the segment behind. In Amphibia (Salamandra) and Aves the secondary tubes develop independently in the mesoblast. These great differences in development are important in reference to the homology of the metanephros or permanent kidney, which is discussed below.

Before leaving the mesonephros it may be worth while putting forward some hypothetical suggestions as to its origin and relation to the pro


732 GENERAL CONCLUSIONS.

nephros, leaving however the difficult questions as to the homology of the segmental tubes with the segmental organs of Chastopods for subsequent discussion.

It is a peculiarity in the development of the segmental tubes that they at first end blindly, though they subsequently grow till they meet the segmental duct with which they unite directly, without the latter sending out any offshoot to meet them 1 . It is difficult to believe that peritoneal infundibula ending blindly and unprovided with some external orifice can have had an excretory function, and we are therefore rather driven to suppose that the peritoneal infundibula which become the segmental tubes were either from the first provided each with an orifice opening to the exterior, or were united with the segmental duct. If they were from the first provided with external openings we may suppose that they became secondarily attached to the duct of the pronephros (segmental duct), and then lost their external openings, no trace of these structures being left, even in the ontogeny of the system. It would appear to me more probable that the pronephros, with its duct opening into the cloaca, was the only excretory organ of the unsegmented ancestors of the Chordata, and that, on the elongation of the trunk and its subsequent segmentation, a series of metameric segmental tubes became evolved opening into the segmental duct, each tube being in a sort of way serially homologous with the primitive pronephros. With the segmentation of the trunk the latter structure itself may have acquired the more or less definite metameric arrangement of its parts.

Another possible view is that the segmental tubes may be modified derivatives of posterior lateral branches of the pronephros, which may at first have extended for the whole length of the body-cavity. If there is any truth in this hypothesis it is necessary to suppose that, when the unsegmented ancestor of the Chordata became segmented, the posterior branches of the primitive excretory organ became segmentally arranged, and that, in accordance with the change thus gradually introduced in them, the time of their development became deferred, so as to accord to a certain extent with the time of formation of the segments to which they belonged. The change in their mode of development which would be thereby introduced is certainly not greater than that which has taken place in the case of segmental tubes, which, having originally developed on the Elasmobranch type, have come to develop as they do in the posterior part of the mesonephros of Salamandra, Birds, etc.

Genital ducts. So far the origin and development of the excretory organs have been considered without reference to the modifications introduced by the excretory passages coming to serve as generative ducts. Such an unmodified state of the

1 As mentioned in the note on p. 729 Sedgwick maintains that the anterior segmental tubes of the Chick form an exception to this general statement.


EXCRETORY ORGANS. 733


excretory organs is perhaps found permanently in Cyclostomata 1 and transitorily in the embryos of most forms.

At first the generative products seem to have been discharged freely into the body-cavity, and transported to the exterior by the abdominal pores (vide p. 626).

The secondary relations of the excretory ducts to the generative organs seem to have been introduced by an opening connected with the pronephridian extremity of the segmental duct having acquired the function of admitting the generative products into it, and of carrying them outwards ; so that primitively the segmental duct must have served as efferent duct both for the generative products and the pronepJiric secretion (just as the Wolffian duct still does for the testicular products and secretion of the Wolffian body in Elasmobranchii and Amphibia).

The opening by which the generative products entered the segmental duct can hardly have been specially developed for this purpose, but must almost certainly have been one of the peritoneal openings of the pronephros. As a consequence (by a process of natural selection) of the segmental duct having both a generative and a urinary function, a further differentiation took place, by which that duct became split into two a ventral Mullerian duct and a dorsal Wolffian duct.

The Mullerian duct was probably continuous with one or more of the abdominal openings of the pronephros which served as generative pores. At first the segmental duct was probably split longitudinally into two equal portions, and this mode of splitting is exceptionally retained in some Elasmobranchii ; but the generative function of the Mullerian duct gradually impressed itself more and more upon the embryonic development, so that, in the course of time, the Mullerian duct developed less and less at the expense of the Wolffian duct. This process appears partly to have taken place in Elasmobranchii, and still more in Amphibia, the Amphibia offering in this respect a less primitive condition than the Elasmobranchii ; while in Aves it has been carried even further, and it seems possible that in some Amniota the Mullerian and segmental

1 It is by no means certain that the transportation outwards of the genital products by the abdominal pores in the Cyclostomata may not be the result of degeneration.


734 GENERAL CONCLUSIONS.

ducts may actually develop independently, as they do exceptionally in individual specimens of Salamandra (Fiirbringer). The abdominal opening no doubt also became specialised. At first it is quite possible that more than one pronephric abdominal funnel may have served for the entrance of the generative products ; this function being, no doubt, eventually restricted to one of them.

Three different types of development of the abdominal opening of the Mullerian duct have been observed.

In Amphibia (Salamandra) the permanent opening of the Mullerian duct is formed independently, some way behind the pronephros.

In Elasmobranchii the original opening of the segmental duct forms the permanent opening of the Mullerian duct, and no true pronephros appears to be formed.

In Birds the anterior of the three openings of the rudimentary pronephros remains as the permanent opening of the Mullerian duct.

These three modes of development very probably represent specialisations of the primitive state along three different lines. In Amphibia the specialisation of the opening appears to have gone so far that it no longer has any relation to the pronephros. It was probably originally one of the posterior openings of this gland.

In Elasmobranchii, on the other hand, the functional opening is formed at a period when we should expect the pronephros to develop. This state is very possibly the result of a differentiation by which the pronephros gradually ceased to become developed, but one of its peritoneal openings remained as the abdominal aperture of the Mullerian duct. Aves, finally, appear to have become differentiated along a third line ; since in their ancestors the anterior (?) pore of the head-kidney appears to have become specialised as the permanent opening of the Mullerian duct.

The Mullerian duct is usually formed in a more or less complete manner in both sexes. In Ganoids, where the separation between it and the Wolffian duct is not completed to the cloaca, and in the Dipnoi, it probably serves to carry off the generative products of both sexes. In other cases however only the female


EXCRETORY ORGANS.


735


products pass out by it, and the partial or complete formation of the Mullerian duct in the male in these cases needs to be explained. This may be done either by supposing the Ganoid arrangement to have been the primitive one in the ancestors of the other forms, or, by supposing characters acquired primitively by the female to have become inherited by both sexes.

It is a question whether the nature of the generative ducts of Teleostei can be explained by comparison with those of Ganoids. The fact that the Mullerian ducts of the Teleostean Ganoid Lepidosteus attach themselves to the generative organs, and thus acquire a resemblance to the generative ducts of Teleostei, affords a powerful argument in favour of the view that the generative ducts of both sexes in the Teleostei are modified Mullerian ducts. Embryology can however alone definitely settle this question.

In the Elasmobranchii, Amphibia, and Amniota the male products are carried off by the Wolffian duct, and they are transported to this duct, not by open peritoneal funnels of the mesonephros, but by a network of ducts which sprout either from a certain number of the Malpighian bodies opposite the testis (Amphibia, Amniota), or from the stalks connecting the Malpighian bodies with the open funnels (Elasmobranchii). After traversing this network the semen passes (except in certain Anura) through a variable number of the segmental tubes directly to the Wolffian duct. The extent of the connection of the testis with the Wolffian body is subject to great variations, but it is usually more or less in the anterior region. Rudiments of the testicular network have in many cases become inherited by the female.

The origin of the connection between the testis and Wolffian body is still very obscure. It would be easy to understand how the testicular products, after falling into the body-cavity, might be taken up by the open extremities of some of the peritoneal funnels, and how such open funnels might have groove-like prolongations along the mesorchium, which might eventually be converted into ducts. Ontogeny does not however altogether favour this view of the origin of the testicular network. It seems to me nevertheless the most probable view which has yet been put forward.

The mode of transportation of the semen by means of the mesonephric tubules is so peculiar as to render it highly improbable that it was twice acquired, it becomes therefore necessary to suppose that the Amphibia and


736 GENERAL CONCLUSIONS.

Amniota inherited this mode of transportation of the semen from the same ancestors as the Elasmobranchii. It is remarkable therefore that in the Ganoidei and Dipnoi this arrangement is not found.

Either (i) the arrangement (found in the Ganoidei and Dipnoi) of the Miillerian duct serving for both sexes is the primitive arrangement, and the Elasmobranch is secondary, or (2) the Ganoid arrangement is a secondary condition, which has originated at a stage in the evolution of the Vertebrata when some of the segmental tubes had begun to serve as the efferent ducts of the testis, and has resulted in consequence of a degeneration of the latter structures. Although the second alternative is the more easy to reconcile with the affinities of the Ganoid and Elasmobranch types, as indicated by the other features of their organization, I am still inclined to accept the former ; and consider that the incomplete splitting of the segmental duct in Ganoidei is a strong argument in favour of this view.

Metanephros. With the employment of the Wolffian duct to transport the semen there seems to be correlated (i) a tendency of the posterior segmental tubes to have a duct of their own, in which the seminal and urinary fluids cannot become mixed, and (2) a tendency on the part of the anterior segmental tubes to lose their excretory function. The posterior segmental tubes, when connected in this way with a more or less specialised duct, have been regarded in the preceding pages as constituting a metanephros.

This differentiation is hardly marked in the Anura, but is well developed in the Urodela and in the Elasmobranchii ; and in the latter group has become inherited by both sexes. In the Amniota it culminates, according to the view independently arrived at by Semper and myself, (i) in the formation of a completely distinct metanephros in both sexes, formed however, as shewn by Sedgwick, from the same blastema as the Wolffian body, and (2) in the atrophy in the adult of the whole Wolffian body, except the part uniting the testis and the Wolffian duct.

The homology between the posterior metanephridian section of the Wolffian body, in Elasmobranchii and Urodela, and the kidney of the Amniota, is only in my opinion a general one, i.e. in both cases a common cause, viz. the Wolffian duct acting as vas deferens, has resulted in a more or less similar differentiation of parts.

Fiirbringer has urged against Semper's and my view that no satisfactory proof of it has yet been offered. This proof has however, since Fiirbringer wrote his paper, been supplied by Sedgwick's observations. The development of the kidney in the Amniota is no doubt a direct as opposed to a phylogenetic development ; and the substitution of a direct for


EXCRETORY ORGANS. 737


a phylogenetic development has most probably been rendered possible by the fact that the anterior part of the mesonephros continued all the while to be unaffected and to remain as the main excretory organ during foetal life.

The most serious difficulty urged by Fiirbringer against the homology is the fact that the ureter of the metanephros develops on a type of its own, which is quite distinct from the mode of development of the ureters of the metanephros of the Ichthyopsidan forms. It is however quite possible, though far from certain, that the ureter of Amniota may be a special formation confined to that group, and this fact would in no wise militate against the homology I have been attempting to establish.

Comparison of the Excretory organs of the Chordata and Invertebrata.

The structural characters and development of the various forms of excretory organs described in the preceding pages do not appear to me to be sufficiently distinctive to render it possible to establish homologies between these organs on a satisfactory basis, except in closely related groups.

The excretory organs of the Platyelminthes are in many respects similar to the provisional excretory organ of the trochosphere of Polygordius and the Gephyrea on the one hand, and to the Vertebrate pronephros on the other ; and the Platyelminth excretory organ with an anterior opening might be regarded as having given origin to the trochosphere organ, while that with a posterior opening may have done so for the Vertebrate pronephros 1 .

Hatschek has compared the provisional trochosphere excretory organ of Polygordius to the Vertebrate pronephros, and the posterior Chastopod segmental tubes to the mesonephric tubes ; the latter homology having been already suggested independently by both Semper and myself. With reference to the comparison of the pronephros with the provisional excretory organ of Polygordius there are two serious difficulties :

(1) The pronephric (segmental) duct opens directly into the cloaca, while the duct of the provisional trochosphere excretory organ opens anteriorly, and directly to the exterior.

(2) The pronephros is situated within the segmented region of the trunk, and has a more or less distinct metameric arrangement of its parts ; while the provisional trochosphere organ is placed in front of the segmented region of the trunk, and is in no way segmented.

The comparison of the mesonephric tubules with the segmental excretory organs of the Chaetopoda, though not impossible, cannot be satisfactorily admitted till some light has been thrown upon the loss of the supposed external openings of the tubes, and the origin of their secondary connection with the segmental duct.

1 This suggestion has I believe been made by Fiirbringer. B. III. 47


738 BIBLIOGRAPHY.


Confining our attention to the Invertebrata it appears to me fairly clear that Hatschek is justified in holding the provisional trochosphere excretory organs of Polygordius, Echiurus and the Mollusca to be homologous. The atrophy of all these larval organs may perhaps be due to the presence of a well-developed trunk region in the adult (absent in the larva), in which excretory organs, probably serially homologous with those present in the anterior part of the larva, became developed. The excretory organs in the trunk were probably more conveniently situated than those in the head, and the atrophy of the latter in the adult state was therefore brought about, while the trunk organs became sufficiently enlarged to serve as the sole excretory organs.

BIBLIOGRAPHY OF THE EXCRETORY ORGANS. Invertebrata.

(512) H. Eisig. " Die Segmentalorgane d. Capitelliden." Mitth. a. d. zool. Stat. z. Neapel, Vol. I. 1879.

(513) J. Fraipont. " Recherches s. 1'appareil excreteur des Trematodes et d. Cesto'ides." Archives de Biologic, Vol. I. 1880.

(514) B. Hatschek. "Studien lib. Entwick. d. Anneliden." Arbeit, a. d. zool. Instit. Wien, Vol. I. 1878.

(515) B. Hatschek. "Ueber Entwick. von Echiurus," etc. Arbeit, a. d. zool. Instit. Wien, Vol. in. 1880.

EXCRETORY ORGANS OF VERTEBRATA. General.

(516) F. M. Balfour. "On the origin and history of the urinogenital organs of Vertebrates." yournal of Anat. and Phys., Vol. X. 1876.

(517) Max. Furbringer 1 . "Zur vergleichenden Anat. u. Entwick. d. Excretionsorgane d. Vertebraten." Morphol. Jahrbuch, Vol. IV. 1878.

(518) H. Meek el. Zur Morphol. d. Hani- u. Geschlechtnverkz.d. Wirbelthiere, etc. Halle, 1848.

(519) Joh. Miiller. Bildungsgeschichte d. Genitalien, etc. Diisseldorf, 1830.

(520) H. Rathke. " Beobachtungen u. Betrachtungen u. 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. iibrigen Wirbelthiere." Arb. a. d. zool.-zoot. Instit. Wurzburg, Vol. II. 1875 (522) W. Waldeyer 1 . Eierstock u. Ei. Leipzig, 1870.


1 The papers of Furbringer, Semper and Waldeyer contain full references to the literature of the Vertebrate excretory organs.


BIBLIOGRAPHY. 739


ElasmobrancJdi.

(523) A. Schultz. "Zur Entwick. d. Selachiereies." Archiv f. mikr. Anat., Vol. XI. 1875.

Vide also Semper (No. 521) and Balfour (No. 292).

Cyclostomata.

(524) J. Miiller. " Untersuchungen ii. d. Eingeweide d. Fische." Abh. d. k. Ak. Wiss. Berlin, 1845.

(525) W. Miiller. "Ueber d. Persistenz d. Urniere b. Myxine glutinosa." Jenaische Zeitschrift, Vol. VII. 1873.

(526) W. Miiller. "Ueber d. Urogenitalsystem d. Amphioxus u. d. Cyclostomen." Jenaische Zeitschri/t, 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. n. 1850.

(530) A. Rosenberg. Untersuchungen iib. die Entivicklung d. Teleostierniere. Dorpat, 1867.

Vide also Oellacher (No. 72).

Amphibia.

(531) F. H. Bidder. Vergleichend-anatomische u. histologische Untersitchungen ii. die mdnnlichen Geschleehts- und Harnwerkzeuge 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. Leydig. Anatomie d. Amphibien u. Reptilien. Berlin, 1853.

(535) F. Leydig. Lehrbuch d. Hisiologie. 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. III. 1876.

(538) VonWittich. "Harn- u. Geschlechtswerkzeuge d. Amphibien." Zeit. f. wiss. Zool., Vol. IV.

Vide also Gotte (No. 296).

Amniota.

(539) F. M. Balfour and A. Sedgwick. "On the existence of a head -kidney in the embryo Chick," etc. Quart. J. of Micr. Science, Vol. xix. 1878.

(540 ) Banks. On the Wolffian bodies of the fatus and their remains in the adult. Edinburgh, 1864.

472


74O BIBLIOGRAPHY.


(541) Th. Bornhaupt. Untersuchungen 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 Hiihnerei." Mini. Acad. Imp. Petersbourg, vn. Series, Vol. xxvil. 1880.

(544) Th. Egli. Beitrage zur Anat. und Entwick. d. Geschlechtsorgane. Inaug. Diss. Zurich, 1876.

(545) E. Gasser. Beitrage zur Entwicklungsgeschichte d. Allantois, der Milllcr'schen Gange u. des Afters. Frankfurt, 1874.

(546) E. Gasser. "Beob. iib. d. Entstehung d. Wolff schen Ganges bei Embryonen von Hiihnern u. Gansen." Arch, fiir mikr. Anat., Vol. xiv. 1877.

(547) E. Gasser. "Beitrage z. Entwicklung d. Urogenitalsystems d. Hiihnerembryonen." Sitz. d. GeseU. zur Befdrderung d. gesam. Naturwiss. Marburg, 1879.

(548) C. Kupffer. " Untersuchting iiber 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 Baue u. d. Verrichtungen d. Geschlechtsorgane. Leipzig, 1846.

Vide also Remak (No. 302), Foster and Balfour (No. 295), His (No. 297), Kolliker (No. 298).

Retrieved from ‘https://embryology.med.unsw.edu.au/embryology/index.php?title=The_Works_of_Francis_Balfour_3-23&oldid=372193’
Powered by MediaWiki