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ROBERT W. HEGNER 



ing SO that when the sixteen-cell stage is reached it has become 

 disintegrated into dark staining granules and fragments of vari- 

 ous forms and sizes (fig. 18, E). During the division of the 

 'Keimbahnzelle' (From 16-32 cell stage) these granules and 

 fragments are about equally distributed between the daughter 

 cells (fig. 18, F). A similar distribution takes place in succeed- 

 ing divisions of the primordial germ cells and this is accompanied 

 by a further decrease in the size of the dark staining granules. 



Fig. 18 Polyphemus pediculus (redrawn from Klihn, '11, '13). A, egg with 

 three imrse 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; c, entoderm cell. F, thirty- 

 two-cell stage from vegetative pole. K, primordial germ cells; e, entoderm cells. 



A blastula of 236 cells is figured by Klihn^ which shows at the 

 vegetative pole four primordial germ cells lying next to eight 

 entoderm cells and bordered by twelve mesoderm cells. During 

 gastrulation this group of twenty-four cells becomes smTounded 

 by the ectoderm cells, and the primordial germ cells may then 

 be recognized as the anlage of the reproductive organs. 



Klihn discusses the origin and significance of the 'Nahrzellen- 

 kern,' and compares this structure with similar bodies which have 

 been found in the primordial germ cells of other animals, but is 

 unable to arrive at anv final conclusion. 



