464 GARY N. CALKINS 



tion invariably took place in structurally perfect individuals. 

 These reorganization processes without exception followed 

 the same sequence as that outlined above for the normal ex- 

 con jugant. 



Not only reorganization processes, but the entire life-cycles 

 which these mutilated conjugating individuals passed through 

 showed all of the phenomena characteristic of normal life-cycles 

 and ended in natural death. Thus previous results have shown 

 that conjugation restores vital activities to an optimum; so here, 

 if the individual which started the VXl series had not conju- 

 gated it would have been able to divide on the average 3.5 times 

 per ten days during the remainder of its life-cycle, but it actually 

 divided 14.8 times per ten days during the same period, despite 

 the fact that it had been cut during conjugation. The extent 

 to which vitality had been restored in this protoplasm, there- 

 fore, is represented by 11.3 divisions per ten days. Similarly 

 with the other experimental series derived from this same 

 parental protoplasm, all might have divided at the rate of 3.5 

 times per ten days if they had not conjugated, but, having con- 

 jugated, they divided at the rates of 14.6 (VX2 series), 15.5 

 (VX3 series), and 15.9 (XZ2 series) times per ten days during the 

 same calendar period, and the extent of vitality renewal is 

 indicated by 11.1, 12, and 12.4 divisions, respectively, per ten 

 days. 



The other experimental series, PXl, PX6, PX7, and X75, 

 showed similar results, but the extent of rejuvenescence was 

 less — a fact illustrating another phenomenon which was de- 

 scribed in the second and third of these studies. In the latter 

 especially it was shown that the vitality of normal ex-con ju- 

 gant series varies between rather wide extremes, and that series 

 with low vitality came from parents which were in the weakened 

 condition due to old age at the time of conjugation. 



In order to obtain a standard measure of vitality of an entire 

 series of Uroleptus mobilis, an ideal life-cycle, based upon ex- 

 perimental results since the first isolation of the original individ- 

 ual, was formulated. Such an ideal cycle was represented by 

 a life-history of 300 division days and 350 generations, 175 days 



