72 FEMALE UROGENITAL ORGANS OF PERAMELES, 



solely the median vaginal apparatus and the connective tissue tract 

 leading backwards therefrom, the completion of the passage by a 

 definite independent involution of the urogenital sinus appears to 

 me inexplicable. However, leaving this point aside, since it is 

 only offered by Fletcher as a tentative suggestion based on appear- 

 ances seen in only two specimens, we come to his important 

 conclusion, founded on the examination of the genital organs of 

 eighty females, that the direct opening in Macropods is " more 

 usually . . . formed late in life, probably during pregnancy 

 or at parturition," a conclusion identical Avith that arrived at, in 

 my previous paper (3), for PerameJes. In the present paper I have 

 expressed the opinion that the pseudo-vaginal passage in Peravieles 

 is actually formed at the time of parturition, and I think that the 

 facts herein set forth justify us in concluding that, as in Peramele& 

 so also in Macropods, the median passage is completed during 

 parturition by actual rupture by the embryo of the tissue inter- 

 vening between the posterior end of the median vagina and the 

 sinus urogenitalis. But in those Macropods with a direct opening, 

 owing to the close approximation of the median vagina to the 

 urogenital sinus, the cleft in the connective tissue or pseudo- 

 vaginal passage is either extremely short or, indeed, hardly present 

 where the two cavities are only separated in the virgin by a thin 

 septum. The consequence of this is that the ruptured epithelium 

 of the median vagina and that of the urogenital sinus are able, 

 in the healing process, to extend completely along the very short 

 pseudo- vaginal passage and to become directly continuous with each 

 other. Once formed, the opening of the median vagina into the 

 sinus, in these Macropods, thus becomes a permanent one, while in 

 Peraineles, as has already been pointed out, owing to the great 

 length of the pseudo-vaginal passage, the edges of the opening 

 into the sinus can only unite with each other, and as a consequence 

 the opening is obliterated and has to be temporarily reformed at 

 each succeeding act of parturition. 



Now there are forms even amongst Macropods, e.g., M. major, 

 in which, as Fletcher points out (13, Part ii. p. 10), " unless very 

 exceptionally there is no direct communication even after young 



