100 G. CARL HUBER 



Grosser has figured in his figures 68 and 114, an egg-cylinder 

 of the albino rat which measures nearly 2 mm. in length. The 

 age of this is given as 8| days. So far as may be determined from 

 his figures, the preparation is not described in his text, the age, 

 size, form, and structure of the egg cylinder shown in figure 29 

 and Grosser's figures 68 and 114, are very similar. In Grosser's 

 figures, I see no evidence of his having differentiated between 

 primary embryonic and extraembryonic ectoderm, while the 

 reference letters for ectoderm and entoderm are reversed. Selen- 

 ka's figure 31, plate 45, may be of a similar stage. This figure is, 

 however, too diagrammatic to admit of close study. No differ- 

 ence is shown in the shape and structure of the cells bounding 

 the two parts of the proamniotic cavity. Christiani's figure 

 39 may be of the same stage, but is too schematically drawn. 

 Figure 4 of the article of Widakowich is of a slightly older stage 

 and presents only a part of the egg-cylinder; it is recorded as 

 about 6f days old. The stage under consideration is not figured 

 by Widakowich, although his text description corresponds closely 

 with what has been here presented. 



The next stage and the one with which this communication 

 is to be completed is one of importance since it is characterized 

 by the anlage of the mesoderm. My own observations may be 

 introduced with the consideration of an egg-cylinder, a section 

 of which is presented in figure 31, rat No. 34, 8 days, 17 hours, 

 after insemination. This was cut in the sagittal plane and 

 measures 1.1 mm. by 0.2 mm., of which 0.4 mm. fall to the 

 ectoplacental cone. This egg-cylinder is almost an exact dupli- 

 cate, both in size and form, of that figured in figure 29 of the 

 same age. In the egg-cylinder shown in figure 31, however, 

 there may be observed, to one side, in the region of the junction 

 of the primary embryonic and extraembryonic ectoderm, and 

 between primary embryonic ectoderm and entoderm, a small 

 group of cells which lie in close relation to the ectoderm and 

 constitute early mesodermal cells. The sections of this series 

 pass not exactly parallel to the mid- sagittal plane throughout the 

 whole extent of the egg-cylinder; especially is this true of its an- 

 timesometrial portion, in the region of the primary embryonic 



