148 Life and Death, Heredity and Evolution 



stage in which it is ready to conjugate. Then permit part 

 to conjugate, while the rest are not allowed to do so, and 

 compare the rate of reproduction in the two sets, under 

 identical conditions. Will those that have been allowed to 

 conjugate reproduce more rapidly than the others? 



This experiment was first performed by Richard Hertwig 

 (1889). At the beginning of conjugation in Paramecium 

 he separated some of the pairs before the process had been 

 accomplished, while others he allowed to complete the mat- 

 ing processes ; he then compared the rate of fission in the 

 two sets. Calkins in 1901 similarly compared the rate of 

 fission in a single line derived from an ex-con jugant with 

 the non-con jugant stock from which it came (the experi- 

 ment is described in full by Calkins and Gregory, 1913). 

 I carried out the same experiment on a very large scale 

 in 1913, employing large numbers of lines of both non-con- 

 jugant and con jugant origin, and repeating the experiment 

 many times. Mast (1917) has recently repeated the ex- 

 periment with a number of lines of Didinium, and Calkins 

 (1919) has still more recently carried it out with Uroleptus. 



Furthermore, Maupas (1888 and 1889) made extensive 

 and thorough researches on the same question in many kinds 

 of infusoria, by somewhat different methods. He did not 

 separate pairs that were beginning to mate, as was done 

 in the other experiments, but compared the rate of fission 

 soon after conjugation with the rate after many genera- 

 tions had elapsed since conjugation. 



All these experiments except those which have been re- 

 ported by Calkins, gave concordant results, unfavorable to 

 the idea that conjugation increases the rate of fission. Mau- 

 pas found that there was in none of the cases he studied an in- 

 crease of fission rate after conjugation; nor a decrease as 



