428 JAS. P. HILL. 



Osborn (11, p. 377) records finding in Didelphys Virgi- 

 nian a '^ the fcEtal membranes . . . crowded into the uterine 

 orifices of the vaginae, which indicates that they had been 

 detached from the embryo in the uterus itself;" (3) Stirling 

 (17) furnishes a valuable account of the parturition in Ma- 

 cropus robustus [Osphranter erubescens]. He has 

 shown that in this form the young one passes out through the 

 median vaginal canal ; and that while the ventral portion of 

 the yolk-sac remains in the uterus, interdigitating with the 

 folds of the mucosa, its dorsal portion, remaining attached to 

 the foetus, becomes, as the latter passes down the median 

 vaginal canal, drawn out into a long stalk carrying the three 

 vitelline vessels. The two forms, wallaroo and bandicoot, 

 thus agree in giving birth to the young through a median 

 channel; but the median canal of the one with its definite 

 walls is by no means homologous with the median cleft-like 

 passage of the other ; for while the former is morphologically 

 continuous with the lateral vaginal canals, and is a true epi- 

 theliallv lined tube, the latter has no connection what- 

 ever with the lateral canals, at no time possesses an 

 epithelial lining, and in fact is non-existent prior to 

 the first parturition. 



It may further be pointed out that in the behaviour of their 

 foetal membranes at parturition the two forms exhibit an 

 interesting parallel and contrast. In the wallaroo, while the 

 extra-embryonic allantois has disappeared at birth, the yolk-sac 

 remains persistent in the uterus, and is drawn out into a long 

 cord, which remains connected with the embryo in its passage 

 outwards. In the bandicoot, on the other hand, it is the 

 allantois which similarly remains attached to the embryo by 

 its stalk during its course down the median passage, and 

 which persists in the uterus, while the yolk-sac has entirely 

 disappeared. This parallel behaviour of non-homologous 

 structures, by means of which nutriment is conveyed to the 

 foetus, tends to suggest that the passage of the young outwards 

 is a quite gradual one. 



The discovery of this unique mode of parturition in Pera- 



