2 o6 THE EVOLUTION OF MAN. 



The first modification of the discoidal, three-layered 

 o-erm-area consists in the fact that the cells round its edge 

 increase more rapidly, and accumulate dark granules in their 

 protoplasm. In this way a darker ring is formed, which is 



Pig. 82. — Circular germ. area of a Babbit, distinguished into the central, 

 light-coloured germ-area (area pellucida), and the peripheric dark germ-area 

 (a. opaca). As it makes itself visible through the dark part, the area 

 pellucida appears the darker. 



Fig. 83. — Oval germ-area (a. germinativa). The dull whitish area opaca 

 appears on the outside. 



more or less distinctly marked off from the lighter centre of 

 the germ-disc (Fig. 82). The latter we shall in future call 

 the light germ-area (area pellucida) ; the darker ring we 

 shall call the dark germ-area (area opaca). (In reflected 

 light, as in Fig. 82-84, it appears reversed ; the light germ- 

 area appears dark, because the dark ground makes itself 

 seen from below ; the dark germ-area appears lighter in 

 comparison.) The circular form of the germ-area changes 

 to an elliptic, and immediately afterwards to an oval form 

 (Fig. 83). One end appears broader and more abruptly 



