58 



G. CARL HUBER 



In figure 23, there are reproduced representative sections of 

 five blastodermic vesicles falling to the end of the sixth day after 

 insemination. None of these five vesicles can be regarded as 

 well fixed. All show a certain amount of distortion, much more 

 evident were the entire series of each of the respective vesicles 

 shown. The form of the blastodermic vesicle of the albino 

 rat at this stage of development, as indicated by the molding 

 of the uterine mucosa, is ellipsoid. Their size as in vivo, when 

 distended and of regular outline, again as indicated by the 

 molding of the uterine mucosa, is slightly larger than would be 



_p. ect p ecL- 



Fig. 23 Sections of blastodermic vesicles or blastocysts of the albino rat. 

 X 200. A and C, rat No. 99, 6 days; B, D, E, rat No. 100, 6 days, y.ent., yolk 

 entoderm; p.enl., parietal layer of entoderm; p. ect., parietal or transitory 

 ectoderm. 



supposed from the drawings presented. By reason of this dis- 

 tortion, exact measurements of size cannot be given. 



In A of figure 23, there is reproduced that portion of one of the 

 sections of a blastocyst (rat No. 99, 6 days) which passes through 

 its floor; the thin roof of this vesicle was so folded that its inclu- 

 sion in the drawing was deemed undesirable. However, its 

 floor or the germinal disc, seems to have retained its normal 

 form and structure, presenting when traced through the series 

 a regular concavo-convex, discoidal form. It consists in the 

 main of three layers of cells of polyhedral type; toward the 

 border of the disc, of two layers of somewhat flattened cells, the 

 peripheral layer being continuous with the single layer of cells 



