478 HENRY F. OSBORN. 



the mouth was large, with a much-protruding tongue. The 

 tail was quite long. As a whole, the embryo in size and 

 appearance resembled closely that of the oppossum at birth, 

 except tliat tlie snout was shorter, suggesting that the embryo 

 belonged to one of the short-faced genera — Chironectis, 

 Petaurus, Phalangista, or Phascolarctos. 



Owing to the rupture of the subzonal membrane, as well as 

 the removal of a portion of the yolk-sac, the precise relations 

 of the membranes were difficult to determine. As far as they 

 could be made out the whole was surrounded by a subzonal 

 membrane, within which the yolk-sac was flattened out over a 

 larger area than in the case of the opossum, a fact which was 

 quite consistent with the advanced age of the embryo. The 

 missing portion of the yolk-sac was largely within the sinus 

 terminalis, so that the extent and character of the attachment 

 of the yolk-sac to the subzonal membrane could not be satis- 

 factorily ascertained. The latter was carefully examined, and 

 soon a number of low villi were discovered upon it 

 without the aid of the glass ; they were distributed over an 

 area to which a highly vascular portion of the yolk-sac was 

 adherent, which was, however, just without the limits of the 

 sinus terminalis; what their distribution was within the 

 limits circumscribed by the sinus terminalis could not be 

 be followed, owing to the removal of the latter. In fig. 5 their 

 position is indicated by a number of dots (v) ; as the figure repre- 

 sents the inner view of the yolk-sac, the villi were of course 

 upon the lower surface, their position being more plainly shown 

 in the woodcut (fig. 2, v). The villi are shown in fig. 6 as they 

 appeared in profile under a low objective. They were con- 

 siderably lower than the subzonal upgrowths of the opossum, 

 so that the term villus cannot be given them very accurately. 

 Upon separating the subzonal layer from the yolk-sac, the 

 former was seen to be composed of somewhat flattened cells, 

 which, over the summits of the villi (fig. 6, b), had a truly 

 squamous character, being quite transparent. The separation 

 of the subzonal membrane did not leave the surface of the 

 yolk-sac smooth as in the opossum, but covered with apparently 



