310 G. CARL HUBER 
that a distinct advance in development has taken place. The 
so-called floor of vesicle A, the region of the germinal dise of 
former stages, directed toward the mesometrial border, is mark- 
edly thickened, resulting in an outgrowth toward the mesometrial 
border and an ingrowth into the cavity of the vesicle. The out- 
growth forms the anlage of the ‘Triger’ (Selenka) or the ‘ecto- 
placental cone’ (Duval), and appears to have developed largely 
as a result of an increase in size of the more superficially placed 
cells, since cell proliferation is not marked in this region. It is 
admitted that the critical stages are here lacking in my material. 
These stages appear to fall to the early hours of the seventh 
day, the material for which is lacking. 
As may be seen from the figure, the cells constituting the an- 
lage of the ectoplacental cone are of relatively large size with 
large vesicular nuclei, and are continuous at the base with the 
parietal ectodermal cells which form the roof of the vesicle or 
its antimesometrial portion. In the cell mass which extends 
into the cavity of the blastodermie vesicle or blastocyst in which 
there is recognized the anlage of the ‘egg-plug’—‘Eizapfen,’ or 
‘egg cylinder’—‘Eicylinder’ (Sobotta) there is evident a fairly 
clearly circumscribed compact mass of cells, which stain some- 
what more deeply than the surrounding cells and which may be 
designated as the ectodermal node. It represents the anlage 
of the true ectoderm of the embryo, as may here be stated in 
anticipation of further description. In all of the vesicles of this 
stage of development, even when cut obliquely or in cross section, 
this small nodule of compactly arranged cells is evident. It is 
circumscribed both from the cells of the ectoplacental cone as 
also from the cells lining the blastocele. The metamorphosis 
leading to the formation of the ectodermal node will receive con- 
sideration in a brief general discussion of this stage. The cells 
covering the egg-plug, and surrounding the ectodermal node, 
so far as it extends into the blastocele, are arranged in a single 
layer, forming a dome-shaped membrane, which appears as forced 
into the cavity of the vesicle consequent on development of the 
ectodermal node. This layer of cells constitutes the yolk ento- 
derm, the anlage and differentiation of which has been previously 
