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 

 withdrawal 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 cha7iges 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), l)ut 

 tliinks that it may occur tlien also. Jollos dis- 

 tniguishes such effects from recomlnnation changes 

 in the germ-plasm, that may take ])lace during 

 conjugation, but how the distinction could be made 

 manifest is not evident at all, for granting that 



