52 G. CARL HUBER 



passes through five sections of 10 n thickness, though one of the 

 end sections, the fifth section of the series, seems to have fallen 

 out during manipulations of staining and mounting, since the 

 preceding, or fourth section does not quite complete the series. 

 This vesicle lies free in the lumen of the uterus, and there is evi- 

 dent only a shallow pit in the mucosa juxtaposed. In this 

 vesicle the cells forming the roof of the segmentation cavity are 

 relatively numerous, and are not markedly flattened, and in one 

 an early mitotic phase is recognized. Here again cell prolifer- 

 ation appears to have accompanied increase in size of segmenta- 

 tion cavity. 



The vesicle shown in C of figure 22, measuring 130 n by 30 n 

 by approximately 40 n, lies free in a long, narrow fold of the 

 uterine mucosa, in close proximity to a shallow mucosal pit, 

 lined by cubic epithelium; the pit conforming in shape and 

 extent to the form of the side of the vesicle presented to it. 

 Therefore, it would seem that the form of the vesicle as seen in 

 sections of the fixed material is essentially the same as that 

 obtained in vivo. The two vesicles, typical sections of which 

 are shown in B and C of this figure, are almost in identically the 

 same phase of development, although their form as seen in sec- 

 tions differs markedly. The plasticity of the living blastodermic 

 vesicles is no doubt such that their form is in a great measure 

 dependent on the shape of the mucosal fold in which they are 

 lodged. In D of figure 22, there is reproduced a section of a 

 blastodermic vesicle which points to a stage of development 

 which is slightly more advanced than that shown in previous 

 figures. The vesicle measures 100 /x by 70 /x by approximately 

 50 fi. The roof enclosing the segmentation cavity is slightly 

 folded; a portion of its wall is thus cut tangentially, as shown 

 in the lower left of the figure. The segmentation cavity is 

 distinctly larger than that shown in the preceding figures, and 

 is bounded by a relatively large number of cells, fourteen in that 

 portion of the roof sketched in this figure, one of which is in a 

 mitotic phase. The mass of cells constituting the floor appears 

 as slightly compressed, in consequence of a slight intra vesicular 

 pressure which aided in the enlarging of the segmentation cavity. 



