286 HEREDITY IN THE PROTOZOA 



descendants to selection, the basis of which was 

 the rate of fission. For example, in one experiment 

 he selected fast and slow lines starting with sister 

 individuals. Repeating this selection for 130 days 

 he found that the division rates were slowly in- 

 creased or decreased. If the excess of generations 

 produced by the fast-selected line is expressed "as 

 a percentage of the total number of generations 

 produced by both sets the difference is 6.9 per cent, 

 for the first thirty days; 12.8 per cent, for the next 

 twenty days; 19.3 per cent, for the next thirty 

 days; and 21.2 per cent, for the last fifty days." 

 The number of generations produced per line 

 during 130 days ranges for the first lines from 178 

 to 187, and for the slow line 116 to 128. ''The 

 slowest fast-selected line produced 50 more gener- 

 ations than the fastest slow-selected lines." The 

 difference that had arisen between the two lines 

 was shown to be inherited in the following way. 

 At intervals some of the individuals were reared 

 without selection or else by ''balanced selection." 

 Thus after 80 days of selection two sets were sub- 

 jected to no-selection. It was found that the 

 culture for fast-selection lines still maintained the 

 higher rate. In another test, a difference that had 

 been produced by 80 days of selection, lasted for 

 102 days without selection. When reversed se- 

 lection was carried out, however, the inherited 

 difference was lost " in the same way that it was 

 produced." Moreover it was found that if conju- 

 gation occurred in the fast set or in the slow set 



