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THE AMEBICAN NATUEALIST [Vol. XLIX 



terial, furthermore, whether such conjugation occurs be- 

 tween individuals of the same race, or between individuals 

 of diverse ancestry, the effect is the same in putting off 

 ultimate weakness and death. With repeated conjuga- 

 tions in such a race the ultimate death may be postponed 

 indefinitely, and this was the argument on which Weis- 

 mann's revised theory of potential immortality was based. 



Now it is exactly the same with Woodruff's rhythms. 

 He finds in his long culture repeated instances of ascend- 

 ing and descending division rates in fairly regular alter- 

 nate succession. The descending division rate is stopped 

 by an " internal regulatory phenomenon, endomixis." 14 

 Woodruff and Erdmann, while showing that endomixis 

 is different from conjugation in the absence of a syn- 

 caryon, apparently accept it as equivalent to conjugation 

 in connection with vitality of the protoplasm : 



Endomixis and conjugation may occur simultaneously in different 

 animals of the same culture, thus strongly suggesting that the same gen- 

 eral conditions lead to both phenomena — one animal meeting the con- 

 ditions one way and another by the other, and that both phenomena 

 fill essentially the same place in the economy of life of Paramecium 



Again they say : 



Endomixis does initiate a new rhythm in the life history of Para- 

 mecium, i. e., a period of increased metabolic activity and therefore of 

 reproductive activity, and since its fundamental morphological features 



stationary and migratory micronuclei in conjugation, it lends strong 

 support to the view that the dynamic aspect of conjugation is not 



Throughout the long period of seven years the Para- 

 mecium aurelia protoplasm without conjugation: "has 

 undergone endomixis frequently, undoubtedly on the aver- 

 age once each month" (ibid., p. 495). Hertwig has 

 already shown, as I do above, that asexual endomixis is 

 parthenogenesis, and if, in connection with the problem 

 of vitality, this is equivalent to conjugation, then we are 



14 1 Md., p. 497. 



is/6t'<7., p. 492; the italics at the end are mine, 

 is Ibid., p. 496. 



