20 PETER OKKELBERG 



two or more cells are so grouped as to suggest that they are 

 derived from one cell by division; but since no mitoses are ob- 

 served, the grouping is probably the result of a migration of the 

 cells. The larvae of this stage have begun to feed. An exami- 

 nation of larvae between this and the former stage shows that they 

 begin to feed when they are about 7 mm. long, although a great 

 deal of yolk is still present in the intestinal wall. 



n. Larva 10 mm. long (June 22). This larva was obtained 

 from the creek on June 22nd and is in the neighborhood of 

 seventy days old. The yolk is now all absorbed from the intes- 

 tinal wall and the lumen of the digestive tract is full of diatoms 

 and other organisms upon which the larvae feed. The germ- 

 gland anlagen are in the middle two-thirds of the coelom, but 

 are absent from its cranial and caudal parts. In later stages, 

 when the cells begin to increase in number by division, their 

 range is extended both craniad and caudad. The germ cells 

 are irregularly distributed along the anlagen with no indica- 

 tion of a segmental arrangement. They lie in the mesenchyme 

 on the ventral side of the dorsal aorta and close against the 

 peritoneum, which consists of very flat epithelial cells (fig. 29). 

 Some of the germ cells may project slightly into the coelom, but 

 these projecting cells do not yet form a continuous germ fold. 

 Although the germ cells may lie against the peritoneum, they 

 never form a part of it. They may be distinguished from the 

 epithelial cells and other cells of the same region by their larger 

 size and spherical shape; by their large spherical nuclei, each 

 containing two large nucleoh, and by their clear transparent 

 cytoplasm (fig. 30). Each is surrounded by flat epithelial cells 

 which are similar to those forming the peritoneum. " The germ 

 cells in this stage are absolutely distinct from the cells of 

 the soma, as they appear to be from the time when they are 

 first recognized as germ cells. They have lost all their yolk, 

 but no signs of mitosis could be found. 



At this stage the lumen of the intestine is very much enlarged 

 and many of the cells from the walls of the intestine have been 

 set free into the intestinal cavity (fig. 31). This is the case also 

 in much earlier stages (larvae about 7 mm. long), and suggests 



