294. HEREDITY IN THE PROTOZOA 
certain families whose members possessed a larger 
number of nuclei but were smaller in diameter. 
It is evident, therefore, that other factors than 
nuclei number are also present. Possibly the amount 
of chromatin in the nuclei of these families may be 
different. 
Since selection was also effective in Arcella 
dentata, which has consistently only two nuclei, the 
results here cannot be ascribed to an increase in 
the number of nuclei, but Jennings has suggested 
for Difflugia that ‘“‘the substances determining the 
hereditary characters may be distributed with less 
accuracy than in the higher organisms, so that the 
two products of fission may often receive parts 
that are not equivalent.’”’ Hegner thinks that this 
may be true for Arcella and adds ‘“‘The sudden 
large heritable change (mutations) would, according 
to this suggestion, be due to large qualitative in- 
equalities, and the smaller heritable variations to 
smaller qualitative inequalities during nuclear di- 
vision.”” Root (1918) has likewise carried out se- 
lection experiments with Centropyxis and has re- - 
corded changes following selection. 
How these changes are brought about in the 
Protozoa is by no means evident. Jennings has not 
committed himself to any one interpretation. If 
we were to accept an old and now discredited view 
as to the influence of selection on any “fluctuating” 
character, it might appear that that view was con- 
firmed, namely, that any change that appears in 
an individual will serve as a starting point for 
