342 H. S. JENNINGS 



This appears to indicate that the hnes with slower fission are 

 defective in some way. Of course it is possible, perhaps probable, 

 that under more natural conditions they would have continued 

 to exist, in spite of their slow multiplication. The extremely 

 slow line 16 (conjugant) had lived from December 6 to Feb- 

 ruary 26, a period of two months and twenty days, comprising 

 forty successive generations. But slow multiplication and high 

 mortality are decidedly correlated. 



It had been planned to employ the 64 sets that were kept for a 

 number of different lines in biometrical studies of the inheritance 

 of the fission rate; and in an attempt to determine whether 

 heritable differentiations in fission rate arise in the progenj^ of a 

 single individual multiplying by fission. But the death of all 

 the slow lines, and the extremely slow multiplication of the others 

 for the last weeks of the experiment rendered the extensive data 

 obtained valueless. 



Summary of Experiment 13. We may summarize the results 

 of this entire experiment as follows : 



In a pure strain, all the individuals derived originally from a 

 single one; and all derived from eight successive conjugations with 

 self-fertilization of the strain: 



1. Conjugation decreased the rate of fission. 



2. Conjugation increased greatly the variability in rate of 

 fission. 



3. The differences in rate of fission were found to be inherited, 

 so that in this respect heritable differentiations arise within the 

 pure strain. 



4. These heritable differentiations are due partly, if not 

 entirely, to conjugation, since the latter increases greatly the 

 variability. But whether such heritable differentiation may 

 arise within the pure strain by other means is not determined in 

 this experiment. 



5. A low fission rate is correlated with a high mortality. 

 Conjugation produces many lines with low fission rate; these 

 lines die out in the course of time, if the conditions become 

 severe, although the lines with rapid fission continue to live. 

 But the slow lines may live for many generations (forty in this 

 experiment) . 



