204 GERM-CELL CYCLE IN ANIMALS 
is initiated. The Nebenkern disappears in the 
odcyte soon after the yolk begins to form. The 
chromatin threads in the spermatocytes break down 
and lose their affinity for dyes, but later reappear. 
In the odcyte, on the contrary, the chromatin threads 
persist. Demoll concludes from these observations 
that the Nebenkern always determines the character 
of the germ cells, which, up to its formation, may be 
called indifferent germ cells. He further concludes, 
that, since in dicecious animals sex is determined by 
the accessory chromosomes, in Helix the sexual 
specificity of the Nebenkern must be determined 
by the accessory chromosomes. Such chromosomes 
were described by Demoll (1912a) in a previous 
contribution. 
A similar idea has been expressed by von Voss 
(1914) regarding the differentiation of indifferent 
germ cells in a flat-worm, Mesostoma ehrenbergt. 
In the embryo of this hermaphrodite the germ gland 
is a syncytium containing both the nuclei of future 
odgonia and future spermatogonia. The cytoplasm 
is apparently homogeneous throughout. The forma- 
tion of the odgonia from indifferent germ cells begins 
with the appearance of a “germinal-vesicle stage” ; 
this is followed by an increase in the amount of 
cytoplasm surrounding them. Since the cytoplasm 
appears to be similar in all parts of the syncytium, 
differentiation must be initiated by the nucleus, 
and the suggestion is made that perhaps the accessory 
chromosome may be responsible for the separation 
of the germ cells into odgonia and spermatogonia. 
