Rejuvenescence in Uroleptus. 



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Rejuvenescence without encystment and without nuclear fusion 



in Uroleptus? 



By Gary N. Calkins. 



[From the Department of Zoology, Columbia University.] 



Experiments made during the last two years on Uroleptus 

 mobilis have shown that renewal of vitality follows conjugation, 

 both parents, coming from the same protoplasm and all kept under 

 identical conditions of food and environment. It was also shown 

 that asexual reorganization occurring during encystment, like- 

 wise results in rejuvenescence. 



It was argued that, since the only Mommon phenomenon in 

 conjugation and encystment is the nuclear dissolution and absorp- 

 tion in the protoplasm, the renewal of vitality after each is due 

 to the chemical and physical changes in the protoplasm set up by 

 the addition of relatively large quantities of nucleoproteins added 

 to it. To test this working hypothesis the following experiments 

 were undertaken last April and May. Individuals of the same 

 ancestry (P series) in the 140th generation, were allowed to con- 

 jugate; a normal ex-conjugant was isolated (V series), and this, 

 with the parent P series, were maintained as controls, the latter 

 to show the degree of vitality without conjugation, the former 

 to show the effect of conjugation. Other pairs of conjugating 

 individuals were isolated in a minute drop of culture medium, 

 a pair at a time, and cut with a scalpel across the angle of the V 

 made by the two individuals in conjugation. The detached angle 

 of the V and one of the arms of the V were immediately fixed 

 and stained to determine the stage of conjugation at the time of 

 cutting. The other part was isolated in culture medium and set 

 aside for observation. Seven pairs were successfully cut in this 

 way, and in the desired plane; four of these died within 10 days, 

 three continued to live forming the X series, the X6 series, and the 

 X7 series. 



The period required for reorganiztion of the normal individual 

 after conjugation and prior to the first cell division, varies from 



