MARSUPIALIA. 
berculate, is again. manifested in this part of 
its structure. The expanded orifices of the 
fallopian tubes present a greater development 
than in the Kangaroo, and are still more re- 
markable for the number, size, and variety of 
the fimbriated processes and folds which aug- 
ment the internal vascular surface of the pavi- 
lion. In both the Wombat and Kangaroo the 
lining membrane of the contracted portion of 
the oviduct is similarly complicated by minute 
and delicate reticular plications and processes. 
The oviducts are shorter and less sinuous in 
their course in the uniparous Kangaroo, fig. 
138, b, than in the multiparous Opossums (6, 
Sig. 139). 
In the above described essential parts of the 
female generative apparatus the mammalian 
type of structure is closely adhered to; the de- 
viations most characteristic of the implacental 
group begin to manifest themselves in the re- 
maining parts, and here under so irregular and 
complicated a form as to require a brief review 
of the analogous structures in other groups of 
animals for their intelligibility. 
The variations of structure which the female 
generative organs present in the oviparous 
classes of Vertebrata are fewer and of less de- 
gree than those observable in the different orders 
and genera of the Mammalia. The most pre- 
vailing characteristic of the oviparous type of 
the female generative organs is the absence of 
union in the mesial plane of the lateral efferent 
tubes, which consequently continue separate to 
their terminations in the excretory outlet. 
In Birds the genital apparatus is characterised 
by the higher, and, in the female, as far as 
function is concerned, exclusive development 
of the left moiety ; and the uniformity in the 
condition of the excluded ovum in this class 
corresponds with the sameness which po 
in the structure of the organs concerned in its 
production. 
In Reptiles the ovaries and efferent parts of 
the genital system are equally developed, or 
nearly so, on both sides. But although a con- 
siderable uniformity of structure is found to pre- 
vail in this system throughout the different 
orders of the class, the widest difference obtains 
both in the place of development of the ovum 
and the condition in which it quits its mother. 
No one, e. g., could have predicated from a 
comparison of the structure of the ovaries and 
oviducts in P ssaapcapet and innocuous Serpents 
that any difference existed in the structure and 
development of the ovum, much less that the for- 
mer were ovo-viviparous but the latter oviparous; 
or, froma comparison of the same organs in 
Lacerta crocea and Lacerta agilis, that a like 
difference should exist in the generative eco- 
nomy of species so nearly allied as for a long 
time to have been confounded together by 
naturalists. 
In Mammalia, however, in most of the orders 
of which the connexion of the ovum with the 
uterus is so much more intimate than in the 
preceding classes, the variations in the structure 
of the female sexual organs are more numerous 
and remarkable; and though it be admitted 
that the nature of the fetal coverings and ap- 
315 
pendages results from the original constitution 
and properties of the ovum, yet the modifica- 
tions of the uterus have evidently, in this class, 
a subordinate relation to those differences. 
In tracing the female generative apparatus 
from the human subject through the different 
orders of Mammalia, we find that it approxi- 
mates to the oviparous type of structure in two 
ways, viz., by an obliteration of the os tince, 
which is the characteristic limit between the 
uterus and the vagina in this class; and bya 
gradually increasing division of the uterus and 
vagina until they become two separate tubes 
throughout their entire extent. 
In no mammiferous genus do the female 
organs present that character of unity or con- 
centration, with distinction of parts, which is 
found in the human subject ; for in the lower 
orders, besides the more essential differences 
above-mentioned, there is always an elongation 
of the uterus, with a thinning of its parietes, and 
in general a blending together of the urethral 
and sexual passages. This latter deviation com- 
mences in the Simie, and in the Lemures the 
angles of the uterus begin to elongate and to 
assume the form of cornua. The mesial cleft 
increases, and the cornua preponderate in the 
Carnivora, the Cetacea, the Ruminantia, and 
the Pachydermata; but it is in the Rodentia, 
which present affinities to Birds in other 
parts of their structure, that the uterus is first 
found completely divided into two lateral halves. 
This structure is not, indeed, uniformly met 
with in all the genera of the order; but besides 
the Hare and Rabbit, in which the double 
uterus is allowed to exist by De Graaf and 
Cuvier, a similarly complete division of the 
organ obtains in the genera Sciurus, Arctomys, 
Spalax, Bathyergus, Echimys, Eretizon, (F. 
Cuvier) and Hydrocherus ; while in the genera 
Mus, Cavia, Caelogenys, and Dasyprocta, a 
portion of the true uterus still remains undi- 
vided ; though this part, to which alone the term 
‘ corpus uteri’ can be properly applied, is ex- 
tremely small or rudimental. Nevertheless, 
although the corpus uteri exists in these genera, 
the true vagina is as remarkable for its length 
and capacity as in those in which the corpus 
uteri has ceased to exist. 
Hitherto the vagina has presented itself un- 
der the form of a simple undivided canal, 
communicating with the urethro-sexual passage, 
at least after impregnation by a single aperture. 
But it is a remarkable and interesting fact that in 
the Sloth, in the Mare and Ass, in the Pig, and 
in the Cow, the vagina in the virgin state com- 
municates with the urethro-sexual passage by 
a double aperture, in consequence of being 
traversed by a narrow vertical septum or chord. 
This septum has been described by veterinary 
authors as a hymen in the Mare; the analo- 
gous part in the human subjectalso occasionally 
presents the same structure, and has even been 
observed in some cases to extend as a mesial 
partition inwards towards the uterus. j 
Inthe Marsupialia, where from the small size 
of the foetus at birth a similar conformation is 
permitted to remain as a permanent structure, 
the vagina is in some genera wholly, and in 
