BY JAS. P. HILL. 69 



passage in the Wallaroo (J/, rohiistus), by way of which, as 

 Stirling (10) has shown, the young Wallaroo reaches the exterior. 

 In that comparison, misled by my misinterpretation of the median 

 vaginjie as posterior prolongations of the uteri, J stated that the 

 former passage had " no connection whatever " with the lateral 

 vaginal canals, an erroneous statement which I trust the present 

 paper sufficiently corrects. For it has been demonstrated that 

 the median pseudo-vaginal passage is directly continuous at, and 

 for some time after, parturition with the lumen of the median 

 vagina, and that the latter is formed by the union posteriorly of 

 the two median vaginal canals, which themselves arise develop- 

 mentally as posteriorly directed csecal diverticula, one from each 

 Miillerian duct at the junction of its uterine and vaginal segments. 



Now in young foetal Macropods and other Marsupials, the 

 median vaginal apparatus consists, as in virgin females of 

 Perameles, of two separate cul-de-sacs lying imbedded in the tissue 

 of the genital cord. But whereas in Macropods the two cul-de- 

 sacs extend back in the tissue of the genital cord up to within a 

 comparatively short distance from the anterior end of the sinus uro- 

 genitalis, and eventually coalesce to form a single blindly ending 

 median vagina whose posterior end alone remains imbedded in 

 the tissue of the genital cord; in Perameles, the vaginal cul-de-sacs 

 remain relatively extremely small, do not undergo fusion until the 

 first parturition, and even then the fusion is only partial, are 

 entirely imbedded in the tissue of the genital cord and terminate 

 far remote from the urogenital sinus. 



In virgin females of Macropus, then, the median vaginal 

 apparatus consists of a single long tube, which ends blindly in 

 the tissue l^etween the posterior ends of the lateral vaginal canals; 

 while in virgins of Perameles the homologous apparatus consists 

 of two separate cul-de-sacs, which end blindly in the tissue 

 between the anterior portions of the lateral canals. 



It is thus evident that the median vaginal apparatus remains, 

 as compared with that of Macropods, in an extremely primitive 

 condition, at a stage of development which is early passed through 

 in the foetal Macropod. 



