488 . AUSTIN RALPH MIDDLETON 



tempted with a single individual taken from one of the fast lines 

 of the first set of experiments, giving experiment 2, described 

 below. It was later carried out anew with the progeny of a 

 single 'wild' individual ('third series'). 



Experiment 2-A. Selection among the progeny of a single 

 individual from Experiment 1 . The individual selected for repe- 

 tition of the experiment was one of those belonging to a fast line 

 of the previous experiment. The progeny of this individual 

 did not live well, so that in some cases one or both sets died out 

 before any definite result was obtained. In one case, however, 

 selection of fast and slow sets was continued through nine con- 

 secutive ten-day periods (April 5 to July 3, 1914). During 

 every ten-day period except the first set the fast-selected set 

 produced more generations than the slow-selected one. The 

 results are less striking than in Experiment 1, however, in the 

 fact that on twenty- two days out of the ninety, the slow lines 

 produced more generations than the fast ones. The irregularity 

 appears connected with the high mortality in both sets. How- 

 ever, the average difference in fission rate per line per day in 

 favor of the fast selected set was 0.317 for the first thirty days, 

 0.757 for the second thirty days; and 0.61 for the third thirty 

 days. 



Experiment 2-B. Now the two sets resulting from the ninety 

 days' selection in Experiment 2-A were subjected to balanced 

 selection for ten days. The difference in fission rate persisted 

 to the extent of an average difference in favor of the fast lines 

 of 0.28 generation per line per day, though on one day the slow 

 lines were faster by 0.01 generation per line. Before the end 

 of the next period all lines were dead, owing perhaps to the hot 

 weather. 



Results. The evidence from these two experiments is, so far 

 as it goes, in the same direction as from those of the first set. 

 Selection produced from the progeny of a single individual two 

 sets tliffering hereditarily in average fission rate. 



