HISTORICAL.* 
The changes found in the pathological embryos to be 
described in this memoir are so radical in nearly all specimens 
that it is almost useless to speculate regarding the fate of the 
embryos had they continued to grow to the end of a normal 
pregnancy. Could the circulation be maintained these specimens 
‘might have developed into amorphous monsters, a condition 
which is probable only when there is a normal twin foetus to 
supply the nutrition. In only one of my specimens (No. 87) 
are the possibilities for such a termination present. Here on 
one side of the chorion there is a normal embryo of the third 
week and on the other side a highly developed umbilical 
vesicle with but a rudimentary amnion, but no real body of 
an embryo. In all of the other twin specimens the changes 
in both embryos are radical and identical, so that we could not 
hope to have had the one embryo dependent upon the other 
for its circulation and nutrition. 
In general then the changes in the embryo and its mem- 
brane, due to the inflammatory action in the uterus, are so 
great that if the ovum is not aborted at an early date (as it 
usually is) it is converted into a solid mole which in the 
course of time is likewise expelled. A few specimens, how- 
ever, are but slightly changed, and these would probably have 
grown into some sort of merosomatous monsters had they 
been retained in the uterus. From my experience I am con- 
vinced that in the study of specimens like these we have the 
key by which we can unlock many of the mysteries of 
teratology. 
In my first two communications I carefully avoided 
all speculations on this subject, for I was well aware of the 
sad state this subject is in, and mere speculations would not 
*The data here recorded are taken largely from Ballantyne’s Ante- 
natal Pathology. 
9 
