170 On the Genetics of the Oiliate Protozoa 



still of the same opinion {vide Calkins and Gregdry, lOK^), and many 

 others have at various times concurred. 



103. Yet R. Hertwig (1889) clearly showed that such a conclusion 

 is not justified. He found that the rate of fission is not diminished 

 before conjugation, but rather increased. He performed the ingenious 

 experiment of forcibly separating a pair of prospective conjugants soon 

 after they had united, and cultivating them further. Far from dying, 

 they continued to divide noi-mally for many generations — thus showing 

 that they were not incapable of further multiplication, or in need of 

 " rejuvenation " through conjugation. Hertwig's conclusion was the 

 opposite to that generally drawn (§ 102). He believed that the rate 

 of fission becomes abnormally high before conjugation, and that the 

 sexual act has the effect of diminishing and normalizing it. 



104. Hertwig's experiment has been repeated by Calkins (1902), 

 and on a large scale by Jennings (1913). The latter has dealt with 

 the facts exhaustively, and his conclusion can hardly be disputed. He 

 writes : " In view of the large number of experiments made by Maupas 

 on this point, the absolute agreement of his results with those of 

 Richard Hertwig ; the fact that these men are perhaps the most 

 thorough investigators that have ever worked along these lines ; the 

 further fact that there exist no careful experimental results opposed 

 to these ; and finally, the very large body of evidence presented in the 

 present paper^ all giving the same results — is it not time that the 

 statements or implications that in the infusoria conjugation results in 

 increased reproduction should disappear from the literature of .science ? " 

 The answer is emphatically affirmative. And it should be noted that 

 it sweeps away all arguments that conjugation causes "rejuvenation," 

 " increased vitality," and the like : for this " vitality " itself is ultimately 

 measured by the rate of fission. 



105. The effects of conjugation have been studied in elaborate 

 detail by Jennings (see especially Jemiings 1911a, 1913: Jennings 

 and Lashley, 1913, 1913 a). The extensive nature of his researche.s, 

 the large number of details which he has endeavoured to elucidate, the 

 vast array of facts which he has recorded — all these make his work 

 excessively difficult to understand or to summarize. It can be appre- 

 ciated in the original only. Comparison of experiment with experiment, 

 conclusion with conclusion, leaves me — after devoting much time and 

 attention to the matter — still in doubt as to what all this work really 

 amounts to. Analysis in detail is here impossible, and I must be 



' Jennings (1913). 



