PATHOLOGIC OVA, ALBINO RAT 383 
adjustment was found necessary, none of the right wall of the 
larger egg-cylinder, and only very slightly so of its left wall. 
The slight deviation from the longitudinal axis of the larger egg- 
cylinder made the procedure desirable. It is thought that the 
figure as presented gives correctly the size of the respective egg- 
cylinders, and in all essentials, their relations; the greater part 
of the figure having been drawn from one section. Both of the 
egg-cylinders reveal normal structure for the stages of develop- 
ment attained. The larger one is cut in the coronal plane, as is 
readily determined by the distribution of the mesoderm, one side 
representing a mirror picture of the other. The direction of sec- 
tion in the smaller egg-cylinder, except that it is longitudinal, 
is not to be determined, since before the anlage of the mesoderm, 
a bilateral symmetry cannot be recognized in sections. Since 
these two egg-cylinders are in all essentials of normal form and 
structure, and since their structure is clearly brought out in the 
figure, an extended description of them at this place seems un- 
called for. For respective stages the reader is referred to Part I. 
Attention may be drawn, however, to the fact that the visceral 
entoderm on the contiguous surfaces of the two egg-cylinders is 
less fully differentiated, and shows less absorption of the ma- 
ternal hemogiobin than is seen on the exposed or free surfaces, 
this, no doubt, for mechanical reasons. Further, that in the 
region where the two egg-cylinders are in contact, the parietal 
ectoderm of each can be traced as a distinct layer to the bases 
of the respective ectoplacental cones, showing that each developed 
from a separate ovum. The ectoplacental cones are for a short 
distance distinct. In tracing the sections through the series the 
impression is gained that the ectoplacental cone of one of the egg- 
cylinders overlaps that of the other in such a way that in the 
plane of the sections obtained, one seems continuous with the 
other, as represented in the figure. The boundary between the 
two is not distinct, and it would seem that as a result of pres- 
sure, partial fusion of the two had taken place. The presence 
of two egg-cylinders, enclosed within a single decidual crypt, as 
shown in this figure, with one of them having much smaller size 
and representing a younger stage of development, I believe is 
