FCETAL MEMBRANES OP OPOSSUM AND OTHER MARSUPIALS. 479 



solid papillge, derived from the yolk-sac epithelium. Each of 

 these was found to be provided with a single dilated capillary 

 vessel branching over its summit (fig. 6, a). These papillae, 

 therefore, with their subzonal caps, recalled at once the simplest 

 form of allantoic villi, which Professor Turner represents^ as 

 consisting of a vascular core raised upon the surface of the 

 allantois and covered with a layer of pavement epithelium de- 

 rived from the subzonal membrane. 



The allantois in Specimen 2 consisted of a highly vascular 

 sac, Avith quite a long narrow stalk, Avhich was attached to 

 the embryo just behind the umbilical stalk ; its distal surfiice 

 was covered with capillary vessels ramifying in all directions; the 

 number of main blood-vessels supplying the allantois was not 

 ascertained. This allantois was proportionately larger than in the 

 advanced kangaroo foetus described by Professor Owen; in other 

 respects it had the same appearance. A more important differ- 

 ence was seen in the fact that this sac had a disc-like area of 

 attachment to what was apparently a portionof thesubzonalmem- 

 brane composed of pavement cells. This feature, if confirmed 

 by later observations, is a highly important addition to our 

 knowledge of the foetal membrane of the Marsupials. Unfor- 

 tunately, owing to the torn condition of the subzonal mem- 

 brane, this point cannot be considered by any means certainly 

 established. 



The uncertainty which existed as to the generic and specific 

 character of Specimen 2, and the difficulty of a positive deter- 

 mination of the relation of its membranes, made an examination 

 of the kangaroo foetus very desirable. According to Professor 

 Chapman^s record, the mother was killed fourteen days after 

 impregnation. The embryo was, however, in an earlier stage 

 of development than that of the opossum ;" the visceral clefts 

 were still very distinct; the fore limb was elongated, but the 

 hind limb was a mere bud. The yolk sac, however, was spread 

 over the inner surface of the subzonal membrane very much as 



> ' Journal of Anatomy and Physiology,' vol. xi, p. 34. 



^ II. C. Cluiiimau, ' Proceedings of llie Philadclpliia Academy,' 1S81, part 

 iii, p. 400. 



