76 FEMALE UROGENITAL OKGANS OF PERAMliLES, 



tion by the genital organs as a whole of a persistently embryonic 



condition; while the specialised Macropods have gone on to 



exhaust the possibilities implied in the possession of a median 



vaginal apparatus and have evolved a direct median passage, 



eventually epithelially lined throughout its entire extent. 



Conscious as I am that the last word has not yet been said on 



the evolution of the median passage in Marsupials, and that many 



points still stand in need of explanation, I put forward these few 



remarks and' suggestions on the parturition phenomena in general 



and on the origin of the direct passage, in no dogmatic spirit, but 



in the hope that they may be the means of eventually leading us 



to a better understanding of this, certainly one of the most 



I'emarkable of all the adaptive modifications exhibited by the 



Marsupialia. 



Concluding Remarks. 



At the conclusion of the present series of papers, I hope, with 

 a more complete knowledge of the development of the genital 

 organs in Fei-a7neles, Macropus, and IVichos^irus, to be in a posi- 

 tion to enter into a more extended discussion of the morphology 

 of the genital oi'gans of Peramehs than is possible in the present 

 communication. It will here suffice to bi'iefly direct attention to 

 the more noteworthy features in which the organs of Perameles 

 depart from the more usual Marsupial condition, and thereafter 

 to shortly inquire what light the study of their development 

 throws on the question of the primitiveness or otherwise of the 

 urogenital organs in this genus of Marsupials. 



If we contrast the urogenital oi'gans of Perameles with those of 

 other Marsupials, e.g., JJacropiis, the following features stand out 

 as worthy of remark : — 



(1.) The absence of any sharply mai'ked separation between 

 the uterine and vaginal segments of the organs, the uterus being 

 directly continued into the median vaginal cul-de-sac and its os 

 being extremely ill-defined. 



(2.) The small size and distinctness in the virgin, of the median 

 vaginal cul-de-sacs, their termination at a relatively great distance 

 from the urogenital sinus and their complete investment by the 

 connective tissue of the urogenital strand. 



