358 S. O. MAST 



that the failure to obtain any effect by conjugation was due to 

 the similarity of the nuclear potency of the conjugants. If this 

 is true it is obvious that our results do not militate against the 

 contentions of Jennings as set forth above. 



SUMMARY 



1. Various groups of pure lines of didinia, all but the first two 

 originating from a single individual, were propagated in parallel 

 series and studied, with certain intermissions, from April, 1910, 

 till May, 1914. During this time there were produced mthout 

 conjugation in one of the groups an average of 1646 generations 

 per line and without encystment an average of 1035 generations 

 per line. At the close the stock was very weak but it did not 

 die out. It is, therefore, not probable that either of these 

 processes is necessary for continued existence in Didinium. 



2. From time to time throughout the entire experiment new 

 groups of lines were started from old ones, some after conjuga- 

 tion, others after encystment and still others without either 

 conjugation or encystment. There were, consequently, con- 

 tinuously present a number of groups of lines which differed in 

 the number of generations produced since conjugation or en- 

 cystment had occurred. In some instances this difference was 

 very great. 



3. The rate of fission varied greatly throughout the experi- 

 ment, owing largely to changes in temperature but at any given 

 time it and also the death-rate were practically the same for all 

 of the groups of lines regardless of the distance removed from 

 conjugation or encystment. There was, therefore, no evidence 

 indicating the presence of cycles related to these processes. 



4. There was no evidence obtained indicating that conjugation 

 or encystment has any appreciable effect on death-rate, fission- 

 rate or variation in fission-rate. This would indicate that 

 neither of these processes is a rejuvenating process, at least not. 

 in the sense in which Calkins has used the term. 



5. In one of the' groups of lines, 721 generations after conju- 

 gation and 197 generations after encystment, some of the off- 

 spring suddenly began to divide more rapidly than others. The 

 difference in the rate of fission in these two sets of individuals 



