20 JAS. p. HILL. 



The vitelline veins (Plate 2, fig. 9, vit. v.) shovsr the usual 

 relations, and include between them a very large ai-ea of 

 yolk-sac splauchnopleure altogether devoid of vessels. The 

 anterior vein is formed by the union in the yolk splauchno- 

 pleure of a larger anterior and a smaller posterior factor, 

 which pass over from the vascular area. There each is 

 formed by the union of lesser factors coming from the capil- 

 lary net of the same. Similarly, the posterior vein is formed 

 by the union of two factors, a smaller anterior and a much 

 larger posterior factor, returning the blood from the poste- 

 rior portion of the vascular area. The anterior vein passes 

 back in the splauchnopleure ovei* the head of the embryo 

 behind the eye, while the posterior one passes in transversely 

 on a level with the snout. The two unite at the yolk-stalk 

 to form the single vitelline vein. 



The allantois is a small, globular, thin-walled vesicle pro- 

 vided with a very short stalk, and measuring in diameter 5'5 

 mm. It is situated mainly on the embryo's right side, lying 

 between the snout and the rounded hinder end of the body. 

 In the figure (Plate 2, fig. 9, all.) it is seen through the 

 yolk splauchnopleure, in contact with which it lies. Its 

 vessels are poorly developed. As Owen long ago pointed 

 out for M. major, and as Semon has recently described for 

 ^pyprymnus, so here the allantois is a quite rudimentary 

 structure which lies remote from the chorionic area, and 

 never comes into contact, much less fusion, with the same. 

 Such a specialised condition of the allantois is probably 

 general for the entire family of the Macropodidse. That it 

 also exists outside the limits of that family we know from 

 the observations of Osborn (10) and Selenka (3) on Didelphys, 

 and probably the condition is also general for the family 

 Phalangeridae — it certainly holds for Petaurus sciurens 

 according to Semon, and from my own observations I can add 

 for Trichosurus vulpecula. But whether the condition 

 may turn out to be the general one for Marsupials or not, it 

 is admitted on all hands to be an essentially modified one, 



Univeksity of Sydney, N.S.W. ; 

 March 16th, 1899. 



