404 MALL. [Vo.. XII. 
between which at one pole of the egg there is a mass of scat- 
tered cells destined to become the permanent ectoderm. The 
outer layer of cells has a tendency to grow into the form of 
villi over the embryonic disc, while on the opposite side of the 
P 

Fic. 1. Fic. 2. 
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Fic. 3. 
Fias. 1-3. — Diagrams of the Development of Pteropus Edulis, after Selenka. Fig. 1 is Selenka’s 
Fig. 2; Fig. 2, Selenka’s Fig. 5; Fig. 3, Selenka’s Fig.9. &, Rauber’s layer; P, placenta; 
ec, ectoderm; ez, entoderm ; c#, chorion; az, amnion; # v, umbilical vesicle; #zes, meso- 
derm ; coe, coelom; ad, allantois, with the arrow indicating the direction of its future 
development. 
egg it is composed of but a single layer of cells. Since this 
outer layer remains well separated from the body of the 
embryo throughout its development, and since it holds the same 
position to the egg that Rauber’s layer does in the rodents, I 
