HEREDITY IN THE PROTOZOA 295 
further changes in the same direction under se- 
lection. If the first change noticed were due to a 
mutation, then the results would not be different in 
principle from those that are observed in higher 
forms, except that it would be necessary to assume 
that such mutational changes are far more frequent 
than is the case in those higher forms -that have 
been investigated. There is also the possibility that 
in the Protozoa the division of the chromatin is 
not as precise as in the ordinary mitotic division of 
higher forms. In fact, when we turn our attention 
to the macronucleus we find that there is no con- 
vineing evidence to show that this nucleus divides 
with the same precision as do the chromosomes of 
the Metazoon cell. ‘Lastly, there is the further 
possibility of unequal distribution of extranuclear 
chromatin (chromidia), which may in some cases 
furnish a basis’ for the differences observed in the 
selection experiments. 
Recently Erdmann (’20) has shown in paramecium 
that progressive changes in form take place between 
two endomictic periods, hence some doubt is cast 
on the value of the earlier results that took no 
account of such a possibility. Moreover, Erdmann 
thinks that after endomixis many new lines may 
appear. If so, this throws further doubts on the 
value of the interpretation of the earlier experiments 
in which endomixis was overlooked. Still other 
doubts arise in consequence of Jollos’ work (21), 
described below. 
Dallinger had experimented in 1887 on the effect 
