78 MALL. [Vou. XIX. 
The amnion is partly within and partly upon the stem of 
the yolk sac in specimen No. 58. In it the mesoderm of the 
chorion, villi, pedicle and sac is fibrous and abnormal in ap- 
pearance. It may be that in this case a portion of the amnion 
broke out of the stem and the portion that remained devel- 
oped into a small vesicle filled with beautiful epithelial cells. 
There are some blood islands within the stem of the vesicle. 
The ccelom is filled with jelly-like magma and the vesicle has 
a granular deposit within it. 
The last specimen of the group is No. 87. Here the yolk 
sac is imbedded in reticular magma and is not connected with 
the chorion. It is covered with a layer of epithelium, which 
at one point is invaginated. Below this layer there is a thick 
mesoderm, in which there are numerous blood islands. The 
chorion is normal. On the opposite side of the ccelom there 
is a normal embryo of the third week with its own umbilical 
vesicle and cord. In this specimen we have twins, one of 
which is normal and the other has undergone this remarkable 
change, found beginning in specimen No. It. 
Multiple amnions.—The last two embryos discussed may 
also be classed under this head, and they therefore represent 
intermediate stages between the two groups. By multiple 
amnions I mean two or more vesicles which arose from the 
original amnion located in the stem of the yolk sac. : 
In these three specimens, Nos. 24, 78 and 247, nothing 
marked is found in the chorion, excepting that of No. 78, in 
which it is atrophic. In this specimen the coelom was found 
filled with fluid; in No. 24 it was filled with a moderate 
amount of reticular magma, and in No. 247 with granular 
magma. 
In No. 24 the stem of the vesicle is broad and contains 
blood-vessels. The endoderm of the yolk sac is well marked 
and from it the allantois arises and branches as it spreads, 
thus forming a multiple allantois. Within the stem there are 
also a number of sharply-defined vesicles, some of which com- 
municate with its epithelial covering. Each vesicle appears 
