MARSUPIALIA. 



315 



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, Jig. 

 138, b, than in the multiparous Opossums ( b } 

 Jig. 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 Vertebruta 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 prevails 

 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 poisonous and innocuous Serpents 

 that any diflerence existed in the structure and 

 development of the ovum, much less that the for- 

 merwere ovo-viviparous but the latter oviparous; 

 or, from a comparison of the same organs in 

 Lacerta crociu and Lacerta agitis, 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 fcetal coverings and ap- 



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 tines, 

 which is the characteristic limit between the 

 uterus and the vagina in this class ; and by a 

 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 Simiee, and in the Lemures the 

 angles of the uterus begin to elongate and to 

 assume the form of ccrnua. 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, 

 SpalaXf Bathyergus, Echimys, Eretizon, (F. 

 Cuvier) and Hydrochterus ; while in the genera 

 MRS, Cuv'iUj Calogem/s, 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 7 

 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 subjectalsooccasionally 

 presents the same structure, and has even been 

 observed in some cases to extend as a mesial 

 partition inwards towards the uterus. 



In the 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 



