320 G. CARL HUBER 
rows of cells than in the one figured; the section figured not pass- 
ing through the center of this structure. In vesicle A, the ecto- 
dermal node, which is distinctly.demarked, no longer rests against 
the base of the ectoplacental cone, as in C of figure 24, but has 
been forced farther into the cavity of the vesicle by reason of 
proliferation of the cells at the base of the ectoplacental cone, 
resulting in the formation of a nearly cylindrically formed column 
of compactly arranged, polyhedral-shaped cells interposed be- 
tween the ectodermal node and the base of the ectoplacental 
cone, but merging into the latter without sharp demarcation. 
To this mass of cells the name of extraembryonic ectoderm has 
been given by Widakowich. However, under this term this 
author includes also the cells of the ectoplacental cone. The 
ectodermal node is of larger size than in the slightly younger 
stage, C of figure 24, the result of cell proliferation. In the 
section sketched, three mitotic figures are evident in this struc- 
ture. Its cells are of polyhedral shape, and show no definite 
arrangement. The ectodermal node and the extraembryonic 
ectoderm, to the base of the ectoplacental cone, together form a 
cylindric structure enclosed within a layer of visceral entoderm, 
which in the section figured is in part cut tangentially, and 
thus simulates an epithelium consisting of two layers of cells, 
but consisting in reality of a single layer of cells. Ectodermal 
node, extraembryonic ectoderm, and the layer of visceral ento- 
derm together form a structure of cylindric shape which ex- 
tends into the cavity of the vesicle for a distance about one-half 
its extent, forming the anlage of the egg-cylinder (Sobotta). 
Very few parietal entodermal cells are to be found on the inner 
surface of the parietal ectoderm. Vesicles B and C of figure 25 
differ from that discussed under A, only to the extent to which 
the ectodermal node has been forced into the cavity of the vesicle 
owing to further growth of the extraembryonic ectoderm, to 
the extent that in C, the elongated egg-cylinder approaches 
the antimesometrial end of the cavity of the respective vesicle. 
Eetodermal node and extraembryonic ectoderm are at this stage 
distinetly demarked, though in close apposition. An indenture 
from the surface at the region of the union of these structures 
