350 MR. OWEN ON THE GENERATION OF THE MARSUPIAL ANIMALS. 



or nearly so, on both sides. But although a considerable uniformity of structure is found 

 to prevail in this system throughout the different orders of the class, the widest dif- 

 ference obtains both in the place of development of the ovum and the condition in 

 which it quits the 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 difference existed in the structure and development of the ovum, much less 

 that the former were ovoviviparous but the latter oviparous ; or, from a comparison 

 of the same organs in Lacerta crocea and Lacerta agilis, that a like difference should 

 exist in the generative economy of species so nearly allied as for a long time to have 

 been confounded together by naturalists. Yet Von Baer has observed that the young 

 of Lacerta crocea are completely developed in the oviduct, and come forth active well- 

 formed lizards. 



These and similar examples from other cold-blooded Ovipara have led him to the 

 conclusion, that the period of intra-uterine existence and the extent of intra-uterine 

 development depend rather upon the original constitution of the ovum than upon 

 the structure of the generative organs ; and they show at least of how little value 

 that opinion of the mode of generation of an animal must be which is founded ex- 

 clusively upon the structure of the efferent portion of the generative apparatus. 



In Mammalia, however, in most of the orders of which the connexion of the ovum 

 to 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 foetal coverings and appendages 

 results from the original constitution and properties of the ovum, yet the variations 

 of the uterus have evidently in this class a relation to those differences. 



In tracing the female generative apparatus from the human subject through the 

 different orders of Mammalia, we find that it approximates to the oviparous type of 

 structure in two ways, viz. by an obliteration of the os tincae, which is the charac- 

 teristic separation of the uterus from 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. Both these modes of deviation combine in the 

 Edentate Marsupiata to give to their generative apparatus its peculiar resemblance 

 to that of the Reptilia. But, for the reasons above mentioned, it would be unwari'ant- 

 able to conclude from the female organs alone of the Ornithorhynchus that its ovum 

 is excluded, as in Birds, with a hard shell, and a corresponding absence of foetal 

 development. 



In no mammiferous genus do the female organs present that character of unity or 

 concentration, 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 Simice. In the Lemures the angles of the uterus begin to elongate 



