436 



ROBERT W. HEGNER 



z U E. 



Fig. 17 Cyclops fuscus var. distinctus {A-G): Diaptomus coeruleus (H), 

 Cyclops vitidis (I); (redrawn from Amma, '11). A, ectosomen at end of first 

 cleavage spindle. B, two-cell stage; ectosomes dissolving. C, old and newly 

 formed ectosomes at end of one of second cleavage spindles. D, eight-cell stage; 

 ectosomes dissolving in stem-cell. E, sixteen- to twenty-eight-cell stage. S, 

 cell with, E, cell without granules. F, one hundred and twelve-cell stage, with 

 two primordial germ cells {U) and three ectoderm cells {E). G, two hundred 

 and forty-cell stage. U, primordial germ cells. H, appearance of ectosomes 

 before cleavage spindle forms. I, increased production due to carbonic acid gas. 



