No. 2.] DEVELOPMENT OF THE HUMAN COELOM. 413 
this explains why the figures here given do not correspond 
exactly with those in previous publications. There cannot be 
any doubt about my interpretation of the arrangement of the 
embryonic layers in this specimen, nor do I think that it is 
abnormal. Yet this last point will be decided in the near 
future, I believe, and therefore it may be dropped until other 
young embryos are described. 
Within the stem of the vesicle there is a sharply defined 
allantois, which communicates with the cavity of the vesicle 

Fic, 12. Fic. 13. 
Fias. 9-13. — Sections No. 43, 53, 68, 80, and 89 through the Embryonic Vesicle of Embryo No. XI. 
Enlarged 33 times. The entoderm is a heavy line, the ectoderm is striated, and the mesoderm 
dotted. a, amnion; X, cavity of the umbilical vesicle extending into the stem of the vesicle ; 
&, Rauber’s layer as the ectoderm of the chorion. 
just below the invagination of the ectoderm. The cavity of 
the vesicle extends into the stem at a lower point, and it is 
this invagination which Graf Spee believes to be the amnion. 
Gladly would I agree with him were it not that there is no 
evidence whatever of the presence of ectoderm at this point. 
Throughout this invagination into the stem there are only two 
thin layers of cells, one of which runs over into the mesoderm 
of the chorion and the other into the entoderm of the vesicle. 
Yet in this invagination the entoderm is not detected at any 
point. 
