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separating the yolk-sac cavities. This fusion aflfects only the non- 

 vascular bilaminar portion of the omphalopleure. 



The chorion, it may here be mentioned, is over a greater or 

 lesser portion of its extent usually closely applied to the uterine 

 epithelium. 



Allantois: The allantois (all.) is in many respects peculiar 

 and differs considerably from that of any other described Marsupial. 

 In shape it is long and band-like, its length several times exceed- 

 ing its breadth. It is usually compressed and wrinkled; and, owing to 

 the thickness of its mesodermal walls, it presents a dense, solid looking 

 appearance. The organ leaves the navel without separation from the 

 amnion and is destitute of any differentiated stalk. It possesses a 

 well developed cavity lined by a moderately thick layer of entoderm. 



In its proportions, the allantois of Dasyur us may be described 

 as well developed, but with regard to its vascularity it certainly 

 exhibits the most degenerate condition hitherto found amongst the 

 Marsupialia. In my two earliest foetal stages the allantois appears 

 as a small thick-walled vesicular organ. In the first it is distinctly 

 vascular but already in the second the vascular supply is found to 

 be reduced. In the next stage, separated by a gap from the pre- 

 ceding, the allantois has increased very considerably in size and 

 assumed its characteristic band-like shape. It now extends through 

 the splanchnocoele and has spread out beneath the chorion, and, in- 

 deed, over small portions of its extent is in such close apposition 

 with the same as to suggest that actual fusion has occurred between 

 the two. Notwithstanding this early attempt at union, the allantois is 

 in the very remarkable condition of being over by far the greater 

 portion of its extent, absolutely devoid of vessels. Foetal blood- 

 corpuscles occur here and there free in the mesoderm of the wall, 

 while close to the navel a quite short and small trunk, the only one 

 recognisable, extends a little way into the organ but is without any 

 very definite central connection. In the embryo even, definite allantoic 

 vessels are hardly recognisable. 



In latter stages, degeneration of the vessels is found to be 

 absolutely complete and the organ is no longer even in contact, much 

 less fusion with the chorion. The allantois of Dasyurus thus comes 

 to lie free in the splanchnocoele as a histologically degenerate, non- 

 vascular, and quite vestigial structure. 



As facts of very special interest I would therefore emphasize 

 1) the abortive attempt of the allantois to unite with the chorion 

 and 2) the rapid complete degeneration of the allantoic vessels. 



