68 G. CARL HUBER 



Vesicle C of figure 24 (rat No. 54, 6 days, 16 hours) presents a 

 stage which is almost identical in development with that shown 

 in B of this figure, though in shape these two vesicles, as seen in 

 sections, appear quite different. The vesicle shown in C is less 

 compressed than the one shown in B, and probably presents more 

 correctly the form of the blastodermic vesicle or blastocyst of 

 the albino rat at this stage of development. The ectoplacental 

 cone presents a cylindrical outline and contains two cells showing 

 mitotic phases, both included in the section figured. Its cells, 

 more particularly the ones bordering the periphery, present a 

 vacuolated protoplasm, the vacuoles containing lightly colored 

 globules which from reaction to the stain are to be regarded as 

 blood cells or fragments of such, which blood cells are regarded 

 as of maternal origin. In this preparation, the decidual crypt 

 contains a small amount of extravasated maternal blood, found 

 in part surrounding the ectoplacental cone ; also in the antimes- 

 ometrial portion of the crypt in relation with the roof of this 

 vesicle. These findings will receive further consideration in the 

 succeeding pages. The cell mass projecting into the cavity of 

 the vesicle, consisting of the ectodermal node and the layer of 

 visceral entoderm is slightly larger than in the preceding stage 

 but presents no special features deserving discussion. The vesi- 

 cle in the section sketched presents very few cells of the parietal 

 entoderm. The parietal ectoderm forming the roof of this 

 vesicle consists of a single layer of flattened cells in the proto- 

 plasm of certain of which vacuolization is evident. Certain of 

 the cells show inclusions of lightly staining globules of a color 

 similar to those found in the cells of the ectoplacenta, particularly 

 evident in the lower right of the figure in which they are repre- 

 sented as uncolored circumscribed areas. The color reaction 

 of these globules is like that of the maternal blood cells and frag- 

 ments of blood cells found in the decidual crypt in the immediate 

 vicinity of the vesicle, and they are regarded as blood cells or 

 fragments of such, taken up by the cells of the parietal ectoderm 

 at this stage in the development of the vesicle. 



The blastodermic vesicles or blastocysts figured in figure 24, 

 represent an important stage in the development of the albino 



