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WILBUR WILLIS SWINGLE 
ering of peritoneum. In cross-section each ridge is seen to be 
made up of several large yolk-laden germ cells and a few small 
deeply staining peritoneal cells. 
2. The two germ ridges enlarge considerably by proliferation 
of the cells and also by migration of mesoderm cells into the 
...J 
Fig. 2 Origin of the germ-cells. A. Cross section through germ-cell region 
of 7-mm. larvae. D, the aorta; E. cardinal veins; F, wolffian duct;(T, lateral 
plate; H, entoderm cells. B. Transverse section through germ-cell region of 
8-mm. larvae. /, germ-cells containing yolk; M, mesentery. C. Low magnifica- 
tion of stage shown in B. ,/, germ cells. 
ridges from the mesonephros and peritoneum. The ridges pro- 
ject into the body cavity and take on the character of germ glands. 
The germ cells lose their yolk at about this time and divide 
actively. 
3. As development progresses, the glands grow rapidly, the 
number of germ cells greatly increasing. Large cavities are 
