374 



OSBORAT. 



[Vol. I. 



attached to the yolk-sac is at this period elevated into numerous 

 hollow villi. ^ Later, I procured for comparison embryos of 

 Hahnaturics and of another undetermined species, possibly 

 Phascolarctos, and observed that the subzonal membrane at- 

 tached to the vascular portion of the yolk-sac was in each case 

 covered with rudimentary villi, and in the specimen last named 

 these villi covered vascular papillae. The membranes were in 

 such a torn condition that the relations could not be pre- 



y-^-~\m 



Figure i. — Didelphys Virginiana. 

 Relations of the foetal membranes 

 at the mid-period of development. 



Figure 2. — Australian Marsupial, undeter- 

 mined. Collection, Cornell University. Mem- 

 branes at a later period. The relations are 

 somewhat conjectural. 



Abbreviations for all the text woodcuts : Al, cavity of allantois. ys, cavity of yolk- 

 sac, am, amnion, ma, my, mesoblast of allantois and yolk-sac. h, hypoblast, yv, 

 low temporary villi of the subzonal membrane, sz, subzonal membrane, sz' , amoeboid 

 area of subzonal membrane, st, sinus terminalis. az',/ermanent allantoic villi. 



cisely determined. In the supposed Phascolarctos embryo (loc. 

 cit, Fig. 2, text, and Fig. 5, Plate XXXIII.) the allantois was, 

 however, seen to be attached to the smooth subzonal membrane. 

 "A number of low villi were discovered upon it {i.e., the sub- 

 zonal membrane) without the aid of a glass ; they were dis- 

 tributed over an area to which a highly vascular portion of the 

 yolk-sac was adherent, which was, however, just without the 



* Iladdon, in his Introduction to the Study of Embryology, p. 89, has slightly mis- 

 understood my account of the Didelphys membranes, when he speaks of " vascular 

 villi " covering the yolk-sac. I intended to make it clear that vascular villi had not 

 been observed in Didelphys, but conjectured that they would be found at a later 

 period. 



