EFFECT OF CONJUGATION 329 



were few in this depressed race that could be induced to multiply 

 sufficiently to furnish the conditions required for conjugation. 

 Those that did conjugate evidently represent then those members 

 of the stock that are most vigorous and active in multiplication. 

 Their later vigor and survival, as compared with the non-conju- 

 gants, may therefore have been due to this, and not to the con- 

 jugation; in other words, conjugation may have been the effect, 

 not the cause, of their greater vigor. If the same individuals 

 that conjugated could have been cultivated without conjugation, 

 it is probable that they would have multiplied equally well or 

 better. 



Hov.-^v^er this may be, it is clear that conjugation did not cause 

 rejuvenescence in any simple direct way, since the majority of 

 the conjugants died out, and those that survived were weak. 

 But in one respect this experiment gives the same results as all 

 others. Conjugation resulted in an increase of variability, as 

 regards vigor and rate of reproduction. Among the extreme 

 variates were some whose vigor was sufficient to keep them alive, 

 while among the more uniform non-conjugants all died. The 

 advantage of the conjugants, so far as it did not exist before con- 

 jugation, is then in this case due to the effect of conjugation in 

 increasing variation. 



Experiment 13: Production of inherited differentiation by conjuga- 



gation: December 6, 1910, to May 15, 1911: 



Paramecium aurelia 



A very extensive and long-continued series of experiments was 

 carried on in the winter and spring of 1910-1911, with the same 

 pure strain k, of Paramecium aurelia, that was used in the experi- 

 ments just described (Experiments 6 to 12). The main purposes 

 of this new set were, to determine whether as a result of conju- 

 gation differentiations may arise within a pure strain, and to 

 bring out the rules of inheritance within the pure strain. Most 

 unfortunately, in the later and most critical part of the experi- 

 ment the conditions became such that multiplication almost 

 ceased, and this made futile a large part of the work, particularly 

 that designed to discover the rules of inheritance. Whether this 



