HEREDITY IN THE PROTOZOA 295 



further changes m 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 possibiUty 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 tuni our attention 

 to the macronucleus we find that there is no con- 

 vincing evidence to show that this nucleus divides 

 with the same precision as do the chromosomes of 

 the Metazoon cell. Lastty, 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 otlier 

 doubts arise in consequence of Jollos' work ('21), 

 described below. 



Dallinger had ex})erimcnted hi 1887 on the effect 



