HEREDITY IN THE PROTOZOA 297 
period, but ultimately there is a return to the 
original ‘“‘reaction-norm.”’ 
Jollos points out that failure to recognize such 
effects has led to much confusion in previous work 
on Protozoa, and he urges that in several of the 
cases mentioned above the so-called effects of 
selection were only ‘“‘temporary modifications” that 
would have disappeared in time if selection were 
withdrawn or the environmental changes that were 
producing them were removed. In a word, that 
many of the cases of inheritance of acquired charac- 
ters, so-called, produced by selection, or otherwise, 
are not comparable to the inheritance of characters 
that have arisen by mutation, which are permanent 
in that the germ-plasm itself has been affected. 
That mutational changes also may arise in the 
Protozoa in consequence of changes in the environ- 
ment during the conjugation period is claimed by 
Jollos. His evidence shows, he believes, that 
mutations were induced both by arsenious acid and 
by high temperature. He states that there is a 
sensitive period at conjugation when mutations may 
be induced by environmental influences that do not 
affect the germ-plasm at other times. He is more 
doubtful as to whether such a sensitive stage is 
present during parthenogenesis (endomixis), but 
thinks that it may occur then also. Jollos dis- 
tinguishes such effects from recombination changes 
in the germ-plasm, that may take place during 
conjugation, but how the distinction could be made 
manifest is not evident at all, for granting that 
