66 G. CARL HUBER 



that a distinct advance in development has taken place. The 

 so-called floor of vesicle A, the region of the germinal disc 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 'Trager' (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 blastodermic 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 



