No. 1.] ORIGIN OF HUMAN MONSTERS. 75 
addition, the changes in the decidua which caused the diffi- 
culty. The equilibrium between the chorion and embryo was 
overthrown at about the same time as in No. 13 and the 
magma became more pronounced than normal. The tissues 
then became dissociated, and on account of lack of nutrition 
they began to disintegrate. 
The next specimen (No. 158) which belongs to this group 
is of about the same age, judging by the size of the chorion. 
It is from a tubal pregnancy and is interesting because there 
are no villi upon the chorion. The main wall of the chorion 
is somewhat fibrous and there are but few epithelium cells 
upon it; these come in direct contact with the lining epithe- 
lium of the tube. The nodule within is as a double sac, partly 
joined by a clump of cells, which runs out into a long process 
containing a blood-vessel (?), but does not join with the 
chorion. The whole mass appears necrotic, at least it does 
not stain well, and probably represents the amnion and yolk 
sac, which come to a sudden end due to the radical changes 
in the chorion. 
The fourth specimen (No. 143) which may be included 
with this group is unique, for within a normal chorion there 
is a double vesicle much larger than the umbilical vesicle ever 
becomes during development. However, the specimen had 
been in alcohol for a long time and the cells are mostly de- 
stroyed, due to bad preservation. The two sacs, which do not 
communicate with each other, are of the same structure as the 
mesoderm of the chorion, to which they are bound by a strong 
pedicle. 
Amnion partly formed.—The five specimens in this group, 
Nos. 11, 396, 134, 58 and 87, are most interesting, and have 
caused me much trouble. Four of them were considered in 
the first communication and need only be reviewed in this place 
in order to make the chain of events complete. 
No. 11 was first described as a normal embryo because its 
chorion and apparently all of its tissues were normal. The 
embryonic mass, however, communicated freely through a 
rounded and natural opening with the ccelom. Furthermore, I 
