50 G. CARL HUBER 



of the two cross diameters. This may be seen from the series of 

 drawings made of a blastodermic vesicle cut cross-wise, taken 

 from the uterus of rat Xo. 68, from which were also taken the 

 two vesicles shown in D and E of figure 20. This series of figures 

 is shown in figure 21, in which are reproduced in serial order 

 the seven successive cross sections into which the vesicle was 

 cut. It measures 65 n by 38 /x by approximately 70 ,u, and is 

 found at the bottom of a mucosal fold, found at the mesometrial 

 border, and is resting with one side on the epithelial lining of 

 a shallow pit, the other wall of this mucosal fold, also showing 

 a shallow pit, is slightly retracted. From a study of this series 



Fig. 21 A complete scries of cross-sections of an early stage of blastodermic 

 vesicle of the albino rat. X 200. Ral No. 68, 4 days and 16 hours. A to C, 

 sections through roof of vesicle, showing segmentation cavity; D to G, sections 

 through floor of vesicle. 



of sections, I feel certain that the plane of section is cross and not 

 oblique to the long axis of the vesicle. The roof of this vesicle 

 passes through three sections, A, B and C. The segmentation 

 cavity has thus a depth of less than 30 p. The overlapping of 

 the cells surrounding the segmentation cavity is to be noted, 

 especially as seen in B of this figure. This arrangement of the 

 cells may explain how the cavity may be enlarged without a 

 material increase in the number of the enclosing cells — in part, 

 by a flattening out of the cells, in part by a rearrangement of the 

 relations of the cells. In the figures of the sections passing 

 through the floor of this vesicle, D to G, attention is drawn to 

 the size, form and relations of the cells and to the fact that there 

 is no distinct covering layer. In this series of sections, there are 



