CONJUGATION AND ENCYSTMENT 337 



Thus we find that Maupas obtained no increase in the rate of 

 fission after conjugation and that both Hertwig and Jennings 

 obtained a decrease. Calkins however still retains his original 

 idea regarding the effect of conjugation on the rate of fission. 

 He says ('13, p. 523) 



Experiments here re-described show that the vitality of a given 

 race is increased by conjugation. An ex-con jiif ant from a pure line 

 that had lived for 369 generations in culture, divided 376 times after 

 conjugation in nine months, while the pure line control that had not 

 conjugated, and from which the ex-conjugant was obtained, divided 

 only 277 times in the same period. 



.Following Fermor ('13) Calkins has recently ('15) extended to 

 encystment the idea that conjugation causes an increase in the 

 vitality of the race. He maintains that there are two kinds of 

 cysts, one kind serving merely to tide over periods of unfavorable 

 enviroimiental conditions, the other serving in the process of 

 nuclear reorganization, structurally and physiologically. Thus 

 he maintains that encystment at times has essentially the same 

 function as conjugation, that it is a rejuvenating process result- 

 ing in an increase in the rate of fission. He presents experi- 

 mental evidence in support of this contention and maintains 

 that it is also supported by the discovery of Woodruff and Erd- 

 mann ('14) that in Paramecium reproducing vegetatively there 

 are periods of depression ending in nuclear reorganization which 

 is followed by increased vigor. 



The experiments described in this paper were continued, with 

 some intermissions, from April, 1910 to May, 1914. They were 

 undertaken primarily to ascertain for Didinium, the relation 

 between conjugation and the rate of fission and to ascertain in 

 general the efTect of preventing conjugation. Aside from the 

 evidence bearing directly on these problems there was, however, 

 considerable evidence obtained which has important bearings 

 on other problems, notably, the function of encystment, vitality 

 of cysts, mutations, the relation between conjugation and 

 death-rate, and variability in the rate of fission. Questions 

 concerning the vitality of cysts and mutations will be discussed 

 in separate papers, which will appear elsewhere; all of the other 

 problems will be considered in the following pages. 



