76 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. 

 Ectodermal node and extraembryonic ectoderm are at this stage 

 distinctly demarked, though in close apposition. An indenture 

 from the surface at the region of the union of these structures 



