PATHOLOGIC OVA, ALBINO RAT 373 
sections of the series which includes this vesicle, which is cut 
in very favorable longitudinal direction, and is thus readily ori- 
ented with reference to mesometrial and antimesometrial por- 
tion, is there seen any thickening of the outer layer of cells, to 
form the part known as the floor of the vesicle, which at this stage 
of development is uniformly directed toward the mesometrial 
border. In A and B of figure 23, Part I, are shown vesicles with 
which the ovum here discussed may be compared. In the 
preparation under discussion, the yolk and parietal entoderm 
form almost a continuous layer, one of the detached cells show- 
ing a mitotic phase. In the normal vesicles of this stage of de- 
velopment the parietal entoderm is represented by a few scat- 
tered cells, as may be observed by a study of the figures to which 
reference is above made. Whether this vesicle is to be regarded 
as showing a later stage of an ovum in which there was irregu- 
larity in the formation of the segmentation cavity, I must for the 
present, leave as problematic. It has occurred to me that by 
enlargement of the segmentation cavity of an ovum such as 
shown in figure 5, with centrally placed segmentation cavity, 
there might result in further development the formation of a 
vesicle such as shown in B of figure 6. 
It is freely admitted that the deductions here made, relative 
to irregularity in the formation of segmentation cavity, are not 
supported by conclusive evidence. It has seemed to me, however, 
that the interpretations given to the appearances presented are 
less open to criticism than others that might be suggested. These 
abnormal ova also suggest an inherent defect in the ova, leading 
to abnormal development, rather than abnormal development 
resulting from defective environment. 
DEGENERATION OF OVA AS RESULT OF PATHOLOGIC 
UTERINE MUCOSA 
In figure 7 are reproduced two ova which seem to me to show 
the primary stages of degeneration owing to pathologic condition 
of the uterine mucosa. Vesicle A was taken from the uterus of 
rat No. 91, 5 days, 16 hours, after insemination. In the uterus 
of this rat there were found only two ova. Vesicle B was taken 
