124 G. CARL HUBER 



seen to the lower left of the figure passes through the series of 

 four 10 M 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 cells of a size comparable to that of the cells forming 

 the floor of the normal blastodermic 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 



