56 



G. CARL HUBER 



such an early differentiation of ectoderm and entoderm as given 

 by Selenka, Duval, Christiani, and others. Cells of irregular 

 outline with tongue-like projections, such as figured by Selenka 

 and Duval I have not observed. The cells constituting the 

 floor or the thick part of the vesicle all present essentially the 

 same structure, while the segmentation cavity, as soon as it 

 presents appreciable size, shows a smooth and regular outline. 

 In figures 1 and 2, of Widakowich's communication, excellent 

 figures of early stages of blastodermic vesicles of the albino rat, 

 there is presented no evidence of a trophoblast layer nor a dif- 

 ferentiation of ectodermal and entodermal cells. My own 

 figures, 20 to 22, were drawn with the aid of camera lucida at a 

 magnification of 1000 diameters and with the use of an intense 

 Welsbach light. They are reduced five limes in reproduction. 

 With the exceptions of cell outlines, which as sketched do not 

 in the preparations fall in the same optical plane, and are sketched 

 more sharply than is perhaps warranted, the figures portray 

 quite accurately the structural appearances presented, so far 

 as may be with the use of a single color. 



BLASTODERMIC VESICLE, BLASTOCYST, OR GERMINAL VESICLE 

 The material on hand is listed in table 6. 



TABLE 6 



During the sixth day, the blastodermic vesicle of the albino rat 

 increases in size relatively rapidly. The greater portion of its wall 

 is, at this stage, composed of a single layer of flattened cells. The 

 vesicles are not as yet attached to the uterine wall, though theuter- 



