220 GERM-CELL CYCLE IN ANIMALS 



not a cell will become a germ cell depends on its posi- 

 tion in the egg just previous to the formation of the 

 blastoderm." 



Similarly in Ascaris the cleavage nuclei are con- 

 ceived as similar so far as their "prospective potency " 

 is concerned, their future depending upon the char- 

 acter of their environment, i.e., the cytoplasm. In 

 the egg of Miastor cleavage nucleus IV (Fig. 15) does 

 not lose part of its chromatin because of the character 

 of the reaction between it and the substance of the 

 *'polares Plasma." In chrysomelid beetles (Hegner, 

 1908, 1909, 1914a) and Chironomus (Hasper, 1911), 

 however, although no diminution process has been 

 discovered in the nuclei that encounter the pole-disc 

 or "Keimbahnplasma," the other nuclei in the egg, 

 so far as known, are similar in this respect. The 

 nuclei of the primordial germ cells, however, may be 

 distinguished easily from those of the blastoderm 

 cells in chrysomelid beetles, proving conclusively 

 that a differentiation has taken place either in one 

 or the other. This differentiation probably occurs in 

 the nuclei that take part in the formation of the 

 blastoderm, since the nuclei of the germ cells retain 

 more nearly the characteristic features of the pre- 

 blastodermic nuclei, whereas those of the blastoderm 

 cells change considerably. 



In some cases the eliminated chromatin may have 

 some influence upon the histological differentia- 

 tion of the cell, since it is differentially distributed 

 to the daughter cells, but in Ascaris and Miastor 

 no mechanism exists for regulating the distribution 



