No. 1.] ORIGIN OF HUMAN MONSTERS. 69 
The proper per cent of real monsters was obtained from 
the 4 per cent of normal embryos. The 14 per cent of mon- 
sters were obtained from the 4 per 100 of normal embryos 
in tubal pregnancy, the remaining 96 having become path- 
ological at a very early stage. This gives, as is shown in 
the table, .56 per cent of monsters for the full 100, which :s 
only a coincidence and an improper comparison. Three of 
the four embryos that remain, that is, those that produce 
normal foetuses, are by no means so according to Von 
Winckel. 
I have given the data obtained from tubal pregnancy at 
some length on account of their bearing upon the etiology 
of teratogenesis. No matter how these data are considered, 
they all point in one direction—the number of pathological 
embryos and monsters is greatly increased in tubal pregnancy. 
PARTIAL OR COMPLETE DESTRUCTION OF THE AMNION, 
LEAVING THE UMBILICAL VESICLE. 
One of the first changes seen in early human embryos is a 
destruction of this important organ, the amnion, which de- 
velops shortly after the umbilical vesicle is formed. We can 
now picture to ourselves pretty well the formation of the 
amnion from the epithelium of the chorion if we blend the 
observation of Selenka upon Hylobates with the very young 
human ovum described by Peters. About the time the ovum 
reaches the uterus, when it is less than 3 mm. in diameter, 
and after the ccelom begins to form there must be an invagi- 
nation of ectodermal cells into the stem of the vesicle within. * 
A portion of the cells of this sac gives rise to the ectoderm of 
the embryo and the rest becomes the epithelial lining of the 
“amnion. * 
It is easy to conceive that any change in the environment 
which influences the growth of the ovum would first make 
