No. 1.] ORIGIN OF HUMAN MONSTERS. 179 
Fic. 87a.—Additional vesicle on the side of the ovum opposite the em- 
bryo. Enlarged 2 times. 
umbilical vesicle. It lies free in the cavity of the ccelom im- 
bedded within the magma, and is in no way torn. It is com- 
posed of three distinct layers: a thick middle layer, in which 
are numerous blood islands, an epithelial lining layer, and an 
outside layer, which does not completely cover the specimen. 
On one side of the vesicle there is a sharp invagination of all 
three layers, which projects well into the vesicle. The meso- 
derm of this: invagination has also within it several blood 
islands. 
The chorion is normal in appearance, with blood-vessels 
entering it from the normal embryo. 
Fic. 87b. Fie. S7c; 
Fics. 87b and 87c—Sections through the vesicle and chorion. X 25 
times. The deeper portion of the invagination in Fig. 87b is shown 
cut in cross-section in Fig. 87c. Blood islands may be seen in the 
mesoderm. 
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