No. 642] VARIATION IN REPRODUCTION 



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Victor Jollos (1921) has just published in this field 

 work which must make a deep impression on the study 

 of experimental evolution, work which gives us more posi- 

 tive results than have before been achieved. By experi- 

 mentation extending over years he has, by subjection for 

 long periods of time, altered the resistance of the infu- 

 sorian Paramecium to certain chemicals, and to heat. 

 After removal of the causative agent these physiological 

 changes are passed on from generation to generation of 

 uniparental reproduction, for longer or shorter periods. 

 Of extreme interest is the fact that longer subjection to 

 the altering agent causes longer persistence after the 

 agent is removed. The induced changes lasted in some 

 cases for hundreds of generations, not yielding at the 

 periodic nuclear reorganizations known as endomixis. 

 But the acquired resistance in practically all cases finally 

 disappeared if the organisms were continued sufficiently 

 long in the normal conditions. Subjection to frequently 

 varied environment hastened the disappearance of the 

 persisting effect ; and it usually disappeared at once when 

 there occurred the profound reorganization accompany- 

 ing conjugation and biparental reproduction. But in 

 some cases, as in Middleton's results, the acquired re- 

 sistance lasted through conjugation ; even through several 

 cycles of conjugation. But in all cases in which it was 

 clear that he was dealing with resistance acquired 

 through subjection to chemical or physical agents, it 

 finally disappeared, after hundreds of generations, if the 

 organisms were kept sufficiently long in an environment 

 lacking the causative agent. Jollos is from this inclined 

 to draw the conclusion that the changes are not com- 

 parable to the (assumedly) permanent differences that 

 separate genotypes' or species, and hence that they do not 

 indicate a method by which such permanent differences 

 may arise. 



Here emerges an obvious logical difficulty involved in 

 all work on the production of inherited change through 

 environmental action. If we succeed in producing such 



