REJUVENESCENCE IN UROLEPTUS MOBILIS 135 



RESULTS OF THE EXPERIMENTS TO DATE 



The physiological effect of conjugation or fertilization in living 

 things has been interpretated, in the main, along two lines of 

 theory. One of these, and the older, may be indicated by 

 Biitschli's term Verjiingung and by Maupas's term rajeunisse- 

 ment — terms indicating that the primary effect of conjugation 

 is to restore the lagging vital activities to an optimum. The 

 other theory, first fully elaborated by Weismann, assumes that 

 the union of germ plasms (amphimixis), brought about by con- 

 jugation, is a source of variation. 



These two theories are not reciprocally exclusive, and it is 

 possible that both are correct, although neither has yet been 

 conclusively established. 



Biitschli interpreted conjugation in the protozoa as a means 

 whereby waning vitality is restored to full metabolic activity. 

 The problem thus suggested involves three fundamental ques- 

 tions: 1) Does the protoplasm of a single individual protozoon 

 and its progeny by division undergo a progressive waning of 

 vital activities leading to 'old age' and finally to natural death? 

 2) Does conjugation actually restore such weakening protoplasm 

 to a condition of full metabolic activity? 3) If conjugation 

 accomplishes this, what is the explanation of the result? 



The first of these questions has been answered in the affirmative 

 by the experiments of Maupas and of subsequent investigators. 

 The second has never been answered conclusively, although 

 strong experimental evidence has accumulated in support of the 

 affirmative. The third question, obviously, is dependent on the 

 second, and at best can be answered only hypothetically on the 

 basis of our present knowledge. 



1. Does the protoplasm of a single individual Uroleptus mobilis 

 and its progeny by division undergo progressive waning of vital- 

 ity and natural death if conjugation and parthenogenesis are 

 prevented? 



Table 2 and diagram 1 based upon it show clearly enough that 

 this question is answered in the affirmative. Series A, C, D, F, 

 G, and H, all started as ex-con jugants, show the same initial 



THE JOURNAL OF EXPERIMENTAL Z05L0GY, VOL. 29. NO. 2 



