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 
