170 GERM-CELL CYCLE IN ANIMALS 



many of Amma's results and has pointed out the 

 similarities between the cell lineage of the COPEPODA 

 and CLADOCERA. Kiihn (1913) has studied the keim- 

 bahn in the summer egg of a cladoceron, Polyphemus 

 pediculus, and has confirmed certain parts and cor- 



FIG. 50. Polyphemus pediculus. A. Egg with three nurse cells. 

 B. Egg at close of maturation, n = " Nahrzellenkern." C. Two- 

 cell stage ; view of vegetative pole. D. Eight- to sixteen-cell stage. 

 K = " keimbahnzelle." E. Sixteen- to thirty-cell stage, e = en- 

 tod erm cell. F. Thirty- two-cell stage from vegetative pole. K 

 primordial germ cells ; e = entoderm cells. (From Kuhn, 1911, 1913.) 



rected other portions of the work done by earlier 

 investigators Grobben (1879), Samassa (1893), 

 and Weismann and Ischikawa (1889). In this 

 species usually one (but sometimes two or three) of 

 the nurse cells (Fig. 50) pass into the egg before 

 cleavage. This cell (or cells) becomes embedded 

 near the periphery at the vegetative pole (Fig. 50, 

 B, n). During each of the early cleavage divisions 



