464 AUSTIN RALPH MIDDLETON 



Fig. 4 Curve of the daily differences between the average number of gen- 

 erations per line produced by the fast selected. set and the slow selected set 

 during the fourth and fifth ten-day periods of opposite selection in Experiment 1, 

 (i.e., Exp. 1, part 2.^ The ordinates give the daily differences, the abscissae 

 give the days. 



Experiment 1, part 3. Continued opposite selection, Decem- 

 ber 24, 1913, to January 22, 1914. 



It will be noticed from table 1 and figure 3 that the differ- 

 ences between the average number of generations produced by 

 the fast lines and the slow^ lines during the three consecutive 

 ten-day periods of Experiment 1, part 1, are 2.03, 3.57 and 

 2.40. That is, each fast line produced, on the average, 0.267 

 generation more per day than each slow line during these thirty 

 days. Table 4 and figure 3 show that the corresponding differ- 

 ences for the fourth and fifth ten-day periods of Experiment 1, 

 were 2.43 and 3.57 which gives a daily average difference of 

 0.300 generation per line. This difference, in favor of the 

 average fast line is slightly (0.033 generation), greater than 

 the corresponding difference of Experiment 1, part 1 (0.267 

 generation). Does this mean that on the average, selection is 

 gradually increasing this difference? Experiment 1-A indicates 

 that opposite selection had produced a heritable difference in 

 the average fission rate of the two sets of lines; may this herit- 

 able difference be increased by further opposite selection? 



