No. 1.] ORIGIN OF HUMAN MONSTERS. 107 
come more hyaline, the round cells having diminished in 
number. Most of the central nervous system is fully de- 
stroyed. There are traces left of some of the large blood- 
vessels, the Wolffian ducts and the chorda dorsalis. No. 244 
may be considered together with this specimen, for in it 
radical changes have also taken place. The central nervous 
system is still sharply defined, more so in the brain than in 
the spinal cord. The heart is represented as a mass of cells 
in front of the head. Below this there is an irregular body, 
probably the dissociated liver, composed of epithelial-like 
cells intermixed with some round cells. The rest of the tis- 
sties are of homogeneous structure, with an occasional necrotic 
mass. In the tail end of the embryo there are some blood 
spaces with blood corpuscles, some of which infiltrate the sur- 
rounding tissues. In many respects this specimen resembles 
No. 115, with the difference that it is larger and was prob- 
ably a little older when the pathological process began in it. 
PATHOLOGICAL EMBRYOS OF THE FouRTH WEEK. 
No doubt the reader has noticed that the embryos grow 
more and more resistant as they become older, and this condi- 
tion continues to a more marked degree in those of the 
fourth week. In embryos of the second week pathological 
changes in the chorion were followed by a partial or com- 
plete destruction of the amnion and embryo, while in those 
of the third week it is not always the same organ or tissue 
which resists the influence longest. However, the brain and 
heart are recognizable in most of the specimens. 
When we reach the fourth week we find that the main 
change in the normal embryo is due to the addition of the 
peripheral nervous system, which is associated with a sharper 
delineation of the organs; they begin to assume some of their 
adult characteristics. A normal type with which to compare 
these changes is seen in embryo No. 2, which has become a 
standard. In my description of pathological specimens of the 
fourth week I shall keep this embryo constantly in mind. 
