280 H. S. JENNINGS 



Experiment 14 343 



Experiment 15: Paramecium caudatum; inherited differentiation 



produced by conjugation 343 



Culture methods necessary to secure uniformity of conditions .... 345 



Records; explanation of tables 34 and 35; results 346 



IV. Resume of results : discussion and conclusions 355 



Effect of conjugation on rate of reproduction 356 



Effect of conjugation on mortality 359 



Effect of conjugation on abnormalities 361 



Effect of conjugation on variation 361 



Conjugation and biparental inheritance 367 



Conjugation and the theory of rejuvenescence 367 



General conclusion 376 



Literature cited 378 



Appendix: fundamental tables (tables 29 to 35; 379 



I. INTRODUCTION 



What is the effect of conjugation on the individual or stock 

 that undergoes it? This question reduces experimentally to the 

 following: In what respect does a stock that has conjugated 

 differ from one that is in other respects similar, but has not con- 

 jugated? What difference is produced if half a given stock is 

 allowed to conjugate while the other half is not? 



When one examines the evidence for the conclusions commonly- 

 drawn as to the effects of conjugation on the stock in the in- 

 fusoria, it is curious that almost no direct experimental evidence 

 is found. The conclusions as to the rejuvenating or other physio- 

 logical effects of conjugation are based almost exclusively on 

 reasoning of the following character: ''Since without conjuga- 

 tion such and such processes of degeneration (or other phenomena) 

 occur, it must be that conjugation has the effect of preventing 

 or curing this degeneration (or these other phenomena)." The 

 experimentation is almost all devoted to testing the premise, 

 while direct experimental demonstration that the conclusion is 

 correct, that conjugation actually does rejuvenate (or the like), 

 is almost unattempted. Such exceptions to this generalization 

 as exist we shall later take up in detail. 



There is then need of an investigation in which conjugation 

 itself ^ — rather than what happens without conjugation — ^shall lie 

 at the center of experimentation. Such a study this paper pre- 



