458 Gary N. Calkins. 



and reproduced for from 8 to 20 generations, and with apparently 

 well-organized bodies/ 



One of these successful cases was an ex-conjugant from an 

 endogamous union of two individuals which were separated by 

 not more than eight or ten generations from the ancestral A in the 

 354th generation of my cultures. The other ex-conjugant died 

 out in the iith generation, while the successful one ran through 

 376 generations before showing signs of debility. It went through 

 eight months in culture without beitig stimulated, and died out 

 finally at the end of 376 generations, which was exactly three 

 generations less than the life of the third series of Paramcecium 

 (C series) which I started on June 18, 1902, and carried along in 

 culture until May 30, 1903, when it died out in the 379th generation 

 (see Diagram III).^ 



Unfortunately, this ex-conjugant has not an absolutely clear 

 record, for the first day after the pair had separated, I placed them 

 both in beef extract for 24 hours (December 9, 1901). This 

 experiment had failed a number of times, and I had no reason to 

 believe that it would succeed this time, and, as stated above, one 

 of the two ex-conjugants thus treated died after eleven generations. 

 Although at first I attributed the successful result to this treat- 

 ment, I do not now believe that the beef extract had anything 

 to do with the vigor of the race that followed, and believe 

 that rejuvenescence was accomplished by the conjugation and 

 nothing else. This conclusion is based upon the following facts: 

 (i) Other ex-conjugants similarly treated with the beef extract 

 failed to live; (2) the non-con jugating individuals of the regular 

 series which were treated with the beef extract at the same time 



'See Studies I, table of conjugations opposite p. 174. 



^We have, then, the interesting coincidence of an individual running through 354 

 generations in culture, conjugating with one of its OAvn close relations, and then, as 

 an endogamous ex-conjugant, running through 376 generations more, a total of 730 

 generations. Against this we must set the 742 generations of the main culture 

 series, and the 379 generations of the third series (C) . The close connection between 

 the 379 and 376 is very significant, and were it not for the fact that the first two 

 series, A and B, were at a fatal period of depression at the end of 200 and 190 genera- 

 tions, we might conclude that 370 more or less is the normal length of life of Para- 

 mcecium in culture. 



