REJUVENESCENCE IN UROLEPTUS MOBILIS 143 



Bearing in mind the fact that, during these periods of declining 

 vigor and death, other fihal series derived from their protoplasm 

 through conjugation were living with full vigor, although handled 

 precisely alike and fed at the same times with the same culture 

 m.edium, we are led to the conviction that waning vitality and 

 natural death are inevitable attributes which are inherent in 

 Uroleptus protoplasm, and that the conclusions of Maupas and 

 of subsequent investigators in regard to this phenomenon are 

 fully confirmed. 



£. Does conjugation between two closely related individuals of 

 Uroleptus of the same age result in checking this waning vitality 

 and in restoring the protoplasm to full metabolic activity? 



The conjugation tests are made with individuals of the same 

 age and of the same series, collected on a certain day from the 

 excess individuals after the isolations are made for that day. 

 These excess individuals, sister cells of those continued in the 

 isolation cultures, represent protoplasm the history of which is 

 identical with that of the protoplasm of the isolation cultures. 

 They are placed in a Syracuse dish with an abundance of culture 

 medium. Here they multiply, and their progeny, in the course 

 of two or three weeks, will conjugate, provided they are sexually 

 mature. 



One such pair of conjugating individuals is isolated in fresh 

 culture medium. The two individuals will have separated as 

 ex-con jugants in twenty-four to thirty-six hours, and one of these 

 is isolated to start a filial series. Thirteen such filial series have 

 been started; five of these have completed their full cycles and 

 have died out; eight, in various stages of vitality, are still under 

 observation. 



The question above has already been answered positively by 

 the results shown in table 4. Every ex-conjugant from the A 

 protoplasm, regardless of the phase of vitality in which the con- 

 jugation occurred, shows an average division rate during the first 

 sixty days of life of 17.1 to 17.9 divisions in ten days. Table 4 

 also shows that this is the highest average division rate of all 

 sixty-day periods of the life cycle. Environmental conditions 

 of food, treatment, etc., being the same for parental and filial 



