374 HOYT S. HOPKINS 



when division is at its maximum or shortly afterward. Thus, 

 in the strains of 23k (p. 368) the fission-rate was highest during 

 the second week, and conjugation occurred (in one culture) 

 during the third week. 



All this lends support to the hypothesis that it is the unusual 

 conditions of rapid growth which predispose to conjugation. 

 Circumstances which favor rapid growth may likewise favor 

 conjugation. Abundant nutriment and the presence of reagents 

 which stimulate growth without harming the organisms act in 

 this way, but for these conditions to operate most effectively the 

 organisms themselves must have come from freely conjugating 

 strains, rendered potentially more capable of rapid division 

 through dormancy. 



GENERAL SUMMARY 



The following conclusions regarding the causes and periodicity 

 of conjugation in Paramecium may be drawn from the observa- 

 tions and experiments above set forth. 



1. Various strains of the same species display different degrees 

 of susceptibility, or readiness, to conjugate when taken from a 

 similar environment and grown under like conditions. 



2. They may likewise show diverse reactions as regards conju- 

 gation when subjected to the same experimental conditions, 

 as when treated with a certain salt solution. 



3. A high degree of susceptibility is indicated by a tendency 

 for conjugation to appear in successive 'epidemics' within a given 

 strain and by the relative number of individuals involved. 



4. The observed time interval between conjugation periods 

 in Paramecium caudatum is from four to twelve weeks. Conju- 

 gation was recurrent in culture 38a after six weeks, in 38h after 

 ten weeks. In culture 44« it occurred after seven to eight weeks, 

 and again after twelve weeks, but in the smaller cultures derived 

 from it {Jf-Ifb, c and d) at intervals of about four to eight weeks. 



5. The time interval in Paramecium aurelia is from two to six 

 weeks (pp. 361 and 365). 



6. There exist strains which do not conjugate during long 

 periods of time, and in which, were the conditions maintained 



