82 MALL. [VoL. XIX. 
numerous blood-vessels filled with blood. ‘There are also 
blood-vessels in the chorion in the immediate neighborhood 
of the vesicle, showing that the two were connected at an 
earlier period in their development. 
No doubt this vesicle has gradually degenerated, but has 
hved so long because the blood cells are more resistant than 
any of the other tissues of the embryo, and, therefore, could 
hold the yolk sac intact, more or less. However, it is clear 
that of the structures of the embryo the yolk sac is the last to 
disintegrate when the chorion is affected. 
Ova IN WHICH THE EmMBRYO AND AMNION HAvE BEEN 
DESTROYED, INCLUDING CERTAIN MOLES. 
Under the previous heading those specimens were discussed 
in which most or all of the embryo and amnion had been 
destroyed, leaving only the umbilical vesicle. Various stages. 
of destruction of the umbilical vesicle were also considered. 
Altogether there were 19 specimens which came under this 
heading. Now we have a second group of 29 specimens in 
which the whole embryo, amnion, belly stalk and yolk sac 
are missing, leaving only the main wall of the chorion and 
its villi. 
In the first group a number of the specimens showed fibrous 
changes in the mesoderm of the chorion with more or less 
destruction of the villi with other changes, such as leucocytic 
infiltration or mechanical injury, indicating that the primary 
cause for these changes is located in the environment of the 
ovum rather than within it. 
In the second group, where the change in the embryo mass 
is more radical, greater changes should be found in the 
chorion, and, in fact, this is the case, as a glance at Table III 
will show. The first eight specimens of the group, from Nos. 
298 to 204, inclusive, may be considered together, for in 
many. respects they are alike. They belong to the first weeks 
of pregnancy. 
