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 Cuapocera. Kiihn (1913) has studied the keim- 
bahn in the summer egg of a cladoceron, Polyphemus 
pediculus, and has confirmed certain parts and cor- 
Fie. 50.— Polyphemus pediculus. A. Egg with three nurse cells. 
B. Egg at close of maturation. mn =‘‘ Nahrzellenkern.” C. Two- 
cell stage; view of vegetative pole. D. Eight- to sixteen-cell stage. 
K=“keimbahnzelle.”’ FE. Sixteen- to thirty-cell stage. e = en- 
toderm cell. F. Thirty-two-cell stage from vegetative pole. K = 
primordial germ cells; e = entoderm cells. (From Kiihn, 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 
