1881.] NATURAL SCIENCES OF PHILADELPHIA. 469 



transparent cliorion. The chorion, which was thickened in places, 

 insinuated itself between folds, into which the lining membrane 

 of the uterus was thrown. The chorion was, however, entirely free 

 from villi or villous processes of any kind, and was perfectly 

 separable in its entire extent from the uterine surface. Indeed 

 it was readily turned out of the uterus intact. On opening the 

 chorion, the embr3'0 Kangaroo was seen inclosed in a very delicate 

 amnion, which was easily lacerated. What at once struck me, on 

 opening the chorion, was the large size of the umbilical vesicle 

 and the undeveloped condition of the allantois, which, though 

 small, was undoubtedly present, consisting of a pear-shaped 

 vesicle or diverticulum from the posterior part of the intestine. 

 The umbilical vesicle adhered to the chorion by that part of its 

 surface most remote from the umbilicus. The line of demarkation 

 between chorion and umbilical vesicle being indicated by a circular 

 blood-vessel. When in the fresh condition, the umbilical vesicle 

 was seen to be highly vascular. The blood-vessels that ramified 

 over its surface consisted of two veins and an artery. The veins 

 began as one vessel from the under surface of the liver, which 

 diverged at the umbilicus and united again on the vimbilical 

 vesicle as a terminal or marginal vein, i. e., the circular vein just 

 referred to, and which indicated the line of contact of the umbilical 

 vesicle with the chorion. The third vessel was an artery, and 

 through the mesenteric could be traced to the aorta. These 

 vessels evidently correspond to the omphalo-mesenteric or vitelHiie 

 veins and arteries of other vertebrate embr^^os as seen, for 

 example, in the embryo chick. The disposition of the umbilical 

 vesicle, with reference to the chorion (its large size and vascularity), 

 reminded me also very much of the rabbit or rodent type of 

 development. While, as we have just seen, the umbilical vesicle 

 was in contact with the chorion, the rudimentary allantois, on the 

 contrar}^ hung freely by its pedicle or urachus in the space 

 between the amnion, the stem of the umbilical vesicle, and the 

 chorion. 



When the allantois was first examined, there could be 

 distinctly seen three very fine vessels, two of which appeared to 

 come from the aorta and corresponded therefore to the umbilical 

 or hypogastric arteries of the placental mammals, while the 

 remaining vessel I considered to represent the umbilical vein of 

 the same. The small size of the allantois and the rudimentary 



