KEIMBAHN-DETERMINANTS 219 



to 118). If, therefore, there is a similar difference in 

 all animals in chromatin content between the germ 

 cells and somatic cells, the elimination of chromatin 

 from the latter must take place by the transformation 

 of the basichromatin of the chromosomes into oxy- 

 chromatin which passes into the cytoplasm during 

 mitosis, or else by the more direct method advocated 

 by the believers in the chromidia hypothesis. 



The causes of the diminution of chromatin in As- 

 caris and Miastor are unknown. Recently Boveri 

 (1910) has concluded from certain experiments on 

 the eggs of Ascaris (see p. 177) that in this form it is 

 the cytoplasm in which the nuclei are embedded that 

 determines whether or not the latter shall undergo 

 this process. Kahle (1908) does not explain the 

 cause of the diminution in Miastor. To the writer it 

 seems more important to discover why the nuclei 

 of the keimbahn cells do not lose part of their chro- 

 matin, since the elimination of chromatin during 

 mitosis is apparently such a universal phenomenon. 

 I would attribute this failure of certain cells to under- 

 go the diminution process not to the contents of the 

 nucleus alone but to the reaction between the nucleus 

 and the surrounding cytoplasm. As stated in a 

 former paper (Hegner, 1909a), "In Calligrapha all 

 the nuclei of the egg are apparently alike, potentially, 

 until in their migration toward the surface they 

 reach the ' Keimhautblastem ' ; then those which 

 chance to encounter the granules of the pole-disc 

 are differentiated by their environment, i.e., the 

 granules, into germ cells. In other words, whether or 



