THE ORGANIC CELL 
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most potent external stimulus appears to be food, starvation 
favouring the development of spermatozoa, while a generous 
diet seems to result in a majority of ova. There is no doubt 
that sex as such is not inherited ; what is inherited is merely 
the power to develop into male or female. 
The best example of early differentiation of the germ cells 
Origin of the Primordial Germ-cells, and casting out of the Chromatin 
in the Somatic cells of Ascaris. (Boveri.) 
A. Two-cell stage dividing. B. The same from the side. C. Resulting 
four-cell stage, the eliminated chromatin in the lower pair of cells is clearly 
shown. D. Third-cleavage, repeating the process seen at A and B. 
from the somatic cells is in the case of Ascaris megaloce , phala 
(a threadworm parasitic in the horse). It may here bem en- 
tioned that the egg of Ascaris has been a classical field for 
cytological research, and is especially associated with the 
names of those two really great men, van Beneden and Th. 
Boveri. The eggs are particularly well adapted for minute 
observation on account of their large size, and the clearness 
with which the most complex changes are defined. 
In the case of Ascaris the differentiation of the reproductive 
