Conjugation and Rate of Reproduction 143 



the time elapsed since conjugation became greater. Hertwig 

 found that the descendants of those that had conjugated 

 actually multiplied more slowly than the descendants of their 

 companions that were not allowed to conjugate. Mast found 

 that in Didinium the rate of fission after conjugation is a 

 little slower for a short time ; but soon the rate becomes equal 

 in those that have and those that have not lately conjugated. 

 In my own extensive experiments, with large numbers of 

 lines in both classes, the average fission rate was uniformly 

 less in the lines that had recently conjugated than in those 

 that had not. Conjugation, as we shall see, caused much 

 variation between the diverse lines, in fission rate as well as in 

 other hereditary characters. At the upper extreme of the 

 variation sometimes a conjugant line exceeded in its fission 

 rate the non-con jugant lines. But in most of the lines the 

 rate after conjugation was decidedly less than before; uni- 

 formly the average of the conjugant lines was much below 

 that of the non-conjugant ones. 1 



In Calkins' experiments, on the other hand, the lines which 

 had conjugated showed a more rapid fission rate than those 

 which had not. In his experiment on Paramecium in 1901, in 

 which a single line derived from an ex-con jugant was com- 

 pared with the non-conjugant stock from which it had come, 

 the ex-con jugant line divided 376 times in nine months, 

 while the non-conjugant lines produced but 277 generations. 

 It may be noted that another conjugant line, derived from 

 the mate of the line that produced 376 generations, died out 

 completely after the production of but 11 generations. This 

 illustrates the fact shown on a large scale in my own ex- 

 periments, that conjugation brings about great variation in 



1 The actual comparative rates in certain cases will be given later 

 (page 158). 



