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, 2.e., the 
granules, into germ cells. In other words, whether or 
