BY JAS. P. HILL. 



73 



have been produced," in spite of the fact that the median vagina 

 is well developed and extends down to within a short distance 

 from the sinus. The distance, however, between the posterior end 

 of the median vaginal cul-de-sac and the sinus urogenitalis, appears 

 to be greater in virgins of M. major than in the virgins of species 

 which later possess the direct post-partum communication. 

 Fletcher says in his description of %'ii'ginal genital organs of M. 

 major, " from three specimens sections which were cut differ from 

 those considered above, chiefly in the fact that the cul-de-sac came 

 to an end sooner, and always before the urogenital canal aj^peared 

 in section" (13, Part ii. p. 9). If, then, a pseudo- vaginal passage 

 were developed in M. major during parturition, it would be of 

 greater length than in those forms with a persistent direct opening, 

 and the question thus arises whether, in view of the closure of 

 the direct opening in Perameles after each parturition in association 

 with a long pseudo- vaginal passage, a similar explanation may not 

 account for the apparently anomalous condition in M. major and 

 other forms in which the direct opening appears to be absent 1 



At all events the fact of the closure of the direct opening into 

 the urogenital sinus in Perameles shows us that the mere absence 

 of such is no certain and sufficient criterion on which to decide 

 whether or not the young are born by a direct median passage. 



Finally, as regards parturition, it seems to me that the fore- 

 going discussion sufliciently upholds the conclusion that Perameles, 

 in respect to the phenomena connected with that process, in no 

 way stands alone amongst Marsupials as an aberrant and special- 

 ised type, but quite on the contrary, exhibits more primitive 

 features in the mode of birth of the young than are shown by 

 any other Marsupial hitherto described as possessing a direct 

 median passage. That the direct passage in Perameles is in a 

 much more primitive condition than that of Macropods, will, I 

 think, be admitted without question. Indeed, the condition of 

 the passage in Perameles can only, in my opinion, be regarded as 

 the precursor of the Macropine one and as showing us in use 

 to-day the earliest stage in the evolution of that direct median 

 passage which reaches its highest development in the specialised 



