74 G. CARL HUBER 



half of the ninth day, contained stages which are younger than 

 nearly all of those obtained the latter half of the eighth day. 

 I am unable to state whether this is owing to a retardation in 

 the rate of development of the ova in rats Nos. 17 and 35, or 

 due to an error of record. The record gives date and hour of 

 insemination and of killing, and I have no reason to doubt its 

 accuracy. However, the two rats in question give the only 

 instances of marked deviation from what appears as a normal 

 rate of development as presented by the bulk of my material. 

 Sobotta ('11) has called attention to the difficulty of obtaining 

 successively staged material in the mouse, and cites Kolster as 

 contending: "Man konne auf die Altersbestimmung gar nichts 

 geben." During this stage of development the decidual crypts 

 lodging the ova are deeper than in the preceding stage, their 

 mesometrial portion being narrower, though they are not as 

 yet separated from the uterine lumen. The orientation of 

 the decidual crypts and the contained egg-cylinders is perhaps 

 more readily made than in slightly younger stages, though not 

 definitely enough to insure the cutting of sections in a given 

 plane. Sections of the egg-cylinder cut in the longitudinal 

 plane may be obtained by cutting parallel to the plane of the 

 mesometrium or at right angles to the same. However, it is 

 still largely a matter of chance as to whether the sections ob- 

 tained pass through the midplane or at an angle thereto. 



In figure 25, there are reproduced representative sections of 

 three germinal vesicles taken from the same uterus (rat No. 35, 

 8 days, 18 hours) which show three closely approximated early 

 stages in the development of the egg-cylinder. None of these three 

 vesicles is cut in exactly the mid-longitudinal plane; especially is 

 this true of the ends of the vesicles. Furthermore, the antimes- 

 ometrial portion of each, lower part of the figure, composed of 

 the thin-walled parietal ectoderm, shows a certain amount of 

 folding, so that a portion of each wall is cut en face instead of 

 en profile. The appearances here presented by the antimesome- 

 trial portion of these vesicles is not to be confused with a 'giant 

 cell' formation of this portion of the roof of the vesicle, described 

 by Sobotta in his earlier publications, but corrected and retracted 



