STUDIES ON GERM CELLS 467 



the pole-disc are differentiated by their environment, i.e., the granules, 

 into germ-cells. In other words, whether or not a cell will become a 

 germ-cell depends on its position in the egg just previous to. the for- 

 mation of the blastoderm (pp. 287-288). 



Similarly, in Ascaris, the cleavage nuclei are conceived as similar 

 so far as their 'prospective potency' is concerned, their future 

 depending upon the character of their environment, i.e., the 

 cytoplasm. In the egg of Miastor, the cleavage nucleus IV (fig. 3) 

 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, '08, '09a) and Chironomus 

 (Hasper, '11) however, although no diminution process has been 

 discovered in the nuclei which encounter the pole-disc or 'Keim- 

 bahnplasma,' 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 blasto- 

 derm cells in Chrysomelid beetles (figs. 53, 54), proving conclu- 

 sively that a differentiation has taken place, either in one or the 

 other. This differentiation probably occurs in the nuclei which 

 take part in the formation of the blastoderm since the nuclei of 

 the germ cells (fig. 53) retain more nearly the characteristic 

 features of the preblastodermic nuclei (fig. 55), whereas those 

 of the blastoderm cells (fig. 54) change considerably. 



In some cases the eliminated chromatin may have some in- 

 fluence upon the histological differentiation of the cell, since it 

 is differentially distributed to the daughter cells, but in Ascaris 

 and Miastor no mechanism exists for regulating the distribution 

 of the cast out chromatin and there is consequently no ground 

 for the hypothesis that "in Ascaris those cells which become 

 body cells are the ones that include the cast-off chromosome ends 

 in their cytoplasm, and it will probably be found that these 

 ejected chromosome parts engender such cytoplasmic differen- 

 tiations as characterize the body cells" (Montgomery, '11, p. 192). 



Chromidia. To several of the bodies listed in table 1 on page 

 461 as Keimbahn-determinants has been ascribed an origin 

 from the chromatin of the germinal vesicle. Many cases of the 

 elimination of chromatin from the nuclei of growing oocytes are 



