104 MALL. [Wor soles 
erate when they were 18 days old. A variety of changes 
are found in each specimen which are by no means of the 
same degree, thus permitting their discussion in regular order. 
It is probable that those with the least amount of change in 
them have been under pathological influences for less time 
than in those in which the tissue changes are more marked. 
There are practically no changes in embryo No. 209, and 
for this reason it may be classed with normal specimens. 
However, it appears as if the chorion were atrophic, being 
very thin immediately over the embryo, and the amount of 
magma reticulé within the cclom is greatly increased. 
There are some changes in the amnion, as it has become 
adherent to the embryo over its tail and back, and is wanting 
entirely over its head. There are numerous cells in the sur- 
rounding magma which may have migrated from the meso- 
derm. It is clear that in this specimen the primary trouble 
is in the chorion immediately over the embryo, which receives 
most of its blood-vessels at this stage. The amnion and ccelom 
were next affected, and had the abortion not followed the 
tissues and organs would soon have dissociated. 
' The dissociation of the tissues is well under way in embryo 
No. 246, the chorion of which is somewhat hyaline and the 
amnion greatly distended. Unfortunately, the embryo is 
broken. Enough of it remains, however, to show that the 
central nervous system is distended and partly filled with 
round cells, which seem to be derived from the dissociated 
neural tube. The heart and large blood-vessels are empty, 
and the liver and optic vesicles are wanting. 
The changes in this specimen can be ascribed to the hyaline 
chorion, but it is difficult to understand how this can cause dis- 
tention of the amnion and destruction of the umbilical cord. At 
any rate, the process of dissociation is well illustrated in this 
embryo. The sharp boundaries of the tissues and organs are 
obliterated and the cells which are liberated take on an indif- 
ferent form. With the dissociation of the walls of the blood- 
vessels the blood corpuscles wander out, to be added to the 
dissociated tissues, and convert the whole into an indifferent 
