344 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 83 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 62 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 
