PATHOLOGIC OVA, ALBINO RAT 365 
(the pathologie and the adjacent normal one) would in all proba- 
bility have been enclosed within the same decidual crypt, a con- 
dition exceedingly rare, judging from the material at hand. 
Whether the very close proximity of these two ova bears causal 
relation to the death of one, by reason of the consequent lessen- 
ing of the available pabulum or embryotroph, can only be con- 
jectured. There is at this stage no question of faulty implanta- 
tion, the ova, though presumably permanently lodged, lie free 
in the lumen of the uterus. Whether on the other hand, the 
death of this ovum was the result of some inherent nutritional 
deficit must also remain unanswered. However, this prepara- 
tion may serve to show that ova of the albino rat, after reaching 
the uterine tube, and after apparently normal segmentation, 
may undergo death and dissolution, for reasons which are not 
structurally discernable. 
B of figure 2, rat No. 68, 4 days, 16 hours, after insemination, 
is from the uterus of a rat containing four ova in early stages of 
blastodermic vesicle formation, three of which were sketched 
under D and E of figure 20, and the series of figure 21, Part I. 
The preparation here described lies free in the lumen of the 
uterus, and appears to represent an uncompleted segmentation, 
with cells and nuclei showing cytolysis and chromatolysis. The 
mass is surrounded by a thin membrane regarded as an oolemma. 
_ Normally the oolemma of the segmenting ova of the albino rat is 
lost in the 4-cell stage, now and again in the 2-cell stage. Whether 
the retention of the oolemma may be brought in causal relation 
to the death and dissolution of the enclosed cells is problematic. 
That such causal relation may exist for the ova of the albino rat, 
appears to me as not impossible. This degenerated egg-mass 
presents the only instance of the late retention of the oolemma 
in the albino rat material at my disposal. 
INCOMPLETE OR RETARDED SEGMENTATION 
The blastodermic vesicles presented in figures 3 and 4 have 
been interpreted as showing incomplete or retarded division of 
certain of the cells of early stage morula masses. The probable 
fate of such blastodermic vesicles in further development cannot 
