368 G. CARL HUBER 
seen to the lower left of the figure passes through the series of 
four 10 » sections including this ovum, and in part separates a 
portion composed of relatively small cells from a larger portion 
composed of larger cells. The rate of segmentation of certain 
of the cells composing the upper larger portion of this cell mass 
appears to have been retarded, thus retarding the development 
of the whole mass. This pathologic ovum rests normally in a 
shallow pit of the mucosa, very similar in form and structure to 
the shallow pit lodging the five normal vesicles found in this 
uterus. 
The ovum shown in B of figure 4 was obtained from the uterus 
of rat No. 68, 4 days, 16 hours, after insemination. with four 
normal vesicles showing early stages of blastodermic vesicle for- 
mation. From this uterus was also taken the completely de- 
generated cell mass with persistent oolemma shown in B of figure 
2. This vesicle on superficial observation does not appear to 
depart markedly from the normal appearance for this-:stage. In 
form and size it corresponds closely to the normal ova taken 
from this uterus. The segmentation cavity seems to have de- 
veloped normally. The slight folding of the roof seen to the left 
of the figure is accidental, due to fixation shrinkage, and is 
very similar to folding of the roof to be observed in many of the 
normal preparations of the series. In the floor of the vesicle 
there may be observed three relatively large cells, partly enclosed 
by smaller ce]ls of a size comparable to that of the cells forming 
the floor of the normal blastodermie vesicles of this stage of de- 
velopment. The three relatively large cells, clearly distinguished 
in the figure, are interpreted as showing a retarded segmenta- 
tion. So far as may be determined, their protoplasm and nuclei 
present normal structure, the lowest of the three cells showing 
an early mitotic phase. I am inclined to the opinion that this 
ovum would have continued in development, perhaps in later 
stages showing distinct arrest in development. This hypothesis 
seems warranted on the basis of the study of a vesicle shown in 
C of figure 4, taken from rat No. 54, 6 days, 16 hours, after in- 
semination. Normal stages for the albino rat, taken about the 
middle of the seventh day after insemination, are shown in figure 
