PHYSIOLOGICAL VARIATIONS IN PARAMECIUM 515 



results justify an entirely different interpretation from that, 

 di'awn by Jennings. In the first place the isolated Paramecia 

 weakened, went into the state of depression and all those that 

 had not conjugated finally died. He interprets the weakness 

 and final death to continued cultivation on slides, but he forgets 

 for the moment that Woodi'uff has cultivated P. aurelia similarly 

 on slides for five and one-half years with as yet no signs of depres- 

 sion. His results were fair confirmation of those obtained by 

 Calkins and should be interpreted similarly, not as due solely to 

 the culture method but to the suppression of a normal function 

 of conjugating lines. In the second place the variations appear- 

 ing in the strains subsequent to conjugation in the weakened race 

 may be interpreted as specific results due to the conditions of 

 the organisms on entering into conjugation. Maupas and Cal- 

 kins, as stated above, have shown that the center of conjugation 

 activity, the micronucleus, degenerates in an exhausted race and 

 the differences in vigor observed by Jennings in the ex-conjugants 

 of the weakened race may be interpreted, quite as well, as due 

 to differences in the extent to which such degeneration has pro- 

 gressed, than as evidences of variability due to amphimixis. 

 The variations observed by Jennings seem to us, therefore, to be 

 phenomena due possibly to the physical condition of the organisms 

 on entering into conjugation and to have little bearing on the gen- 

 eral problem of the purpose of conjugation. The same argument 

 applies in the matter of rejuvenescence — the failure of these 

 weakened Paramecia to rejuvenate after conjugation is no proof 

 that conjugation of normal organisms does not rejuvenate. The 

 portion, in Jennings' experiment, in which the organisms were 

 allowed to conjugate, retained their vigor and this fact, in our 

 opinion, justified Biitschli's conclusion ('76) that conjugation is 

 for the purpose of offsetting an on-coming physiological weak- 

 ness and death which is certainly what happened with some of 

 the ex-conjugants of the depressed portion. 



Jennings ('13) does not regard this result as a case of rejuven- 

 escence. ''There was no general rejuvenescence due to conjuga- 

 tion. Three of the six conjugant lines died out within a week, 



