124 GERM-CELL CYCLE IN ANIMALS 
that this phenomenon does not occur in all insects and 
that we must seek some larger cause than the un- 
equal distribution of chromatic elements. 
If no differential divisions are present, as in 
Dytiscus, what is the cause of the formation of 
odcytes and nurse cells? Govaerts decides that since 
the ultimate odgonium possesses a definite polarity 
marked by the localization of the “‘residu fusorial,”’ 
and the two kinds of daughter cells arise from op- 
posite ends of the mother cell, the cause of the differ- 
entiation resides in the polarization of the odgonium. 
He does not, however, account for this ‘‘ polarité pre- 
differentielle.” 
Haecker (1912) has described in Cyclops and 
Diaptomus a three-cell stage in the development 
of the gonad which is brought about by the delayed 
division of one of the germ cells of the two-cell 
stage, and concludes that as in Dytiscus there must 
be an internal difference in the cells to account 
for this condition. 
Wieman (19105) has followed the history of the 
odgonia in Leptinotarsa signaticollis through the 
larval and adult stages, but was unable to find any 
evidence that the nuclei inaugurate differentiation 
as in Dytiscus. He concludes that “the process 
seems to be the result of several distinct cell elements 
which operate together as a whole” (p. 148) and that 
the semi-fluid matrix which results from the lique- 
faction of cells at the base of the terminal chamber 
may exert a “specific effect on those germ cells 
coming under its influence, enabling them to develop 
