146 On the Genetics of the Ciliate Protozoa 



longest lines of which he succeeded in keeping for 860, 44'8 and 288 

 generations respectively. He observed Calkins's "cycles" in division 

 rate (§ 28), with corresponding " depression periods " resulting finally 

 in death. "Rejuvenescence" was brought about by beef extract 

 (Oxijtrichn). "The number of generations which constitute a cycle 

 is not at all constant," and the "cycles" themselves show secondary 

 cycles or "rhythms" — i.e. minor fluctuations in division rate. No 

 conjugations occurred. 



38. Quite recently Woodruff (1913 6) has published some measure- 

 ments of individuals from his long line of Oxytricha. He finds that the 

 mean size of both the organism and the nucleus is " smallest at periods 

 of high reproductive activity, and becoines progressively larger as the 

 division rate falls." During depression periods there is an increase in 

 the relative amount of cytoplasm as compared with nucleus (§§ 31, 32). 

 As Woodruff appears to have selected his individuals at random, at 

 unknown inter-division moments, it is not surprising that he finds the 

 karyoplasmic ratio very variable'. This consideration seems to me to 

 render his measurements of very questionable significance. 



39. In a long series of papers, Woodruff (1908 a-1914)'' has reported 

 upon his investigations of Paramecimn aurelia'. "This race of Para- 

 mecium has attained so far (May 1, 1912) 3029 generations during the 

 five years it has been under daily observation. The number of genera- 

 tions attained during each of the first five years of its existence is as 

 follows : first year 452, second year 690, third year 613, foiirth year 612, 

 and fifth year 662. The mean rate of division for the entire period is 

 over three divisions in forty-eight hours. Periods of marked physio- 

 logical depression have not occurred — such variations in the rate of 

 reproduction as have appeared being either normal rhythms or the 

 effects of environmental changes of temperature and culture medium. 

 The organisms of the present generation are in as normal morphological 

 and physiological condition as the original ' wild ' individual isolated 

 to initiate the culture" (Woodruff, 1912). Later (Woodruff, 1913) we 

 learn that 3340 generations have been reached : still later (Woodruff, 

 1913a) "more than 3800 generations" in "over 6 years"; and finally 

 it is announced (Woodruff, 1914) that the 4102nd generation has been 



' See § 47 infra. 



'■' Summaries of the work of Woodruff and his collaborators will be found in Woodruff' 

 (1912 a) and Middleton (1913). 



' P. caxidatum has given comparable results on a smaller scale. Concerning the 

 specific distinctions of these two farms see Woodruff (1911 b). Compare also § 78 infra^ 



