A PHYSIOLOGICAL CHAKACTER. 



49 



environmental factors (see page 140). However, in 4 of the 5 other 

 two-month periods of the experiment, the minus strain was the more 

 reactive (the combined mean was 42 seconds greater for the plus 

 strain), and it is possible that there really existed a genetic differ- 

 ence between the two strains of this line. 



Perhaps the most that can be said regarding Line 689 is that 

 the persistently lower reaction-time in the minus strain is suggestive 

 of a genetic difference in the reverse of selection. It is much to be 

 regretted that this line could not have been continued longer or that 

 large test series were not conducted in order to secure better evidence 

 concerning the real persistence of this apparent difference in reaction- 

 time. 



With regard to any relation between mean reproductive vigor 

 and mean reaction-time in Line 689, it may be said that no relation is 

 discoverable. On the whole, the plus strain was somewhat the more 

 vigorous (see figure 3, a and b) while the minus strain was the more 

 reactive. Further, there is an entire lack of coincidence of lowered 

 reaction-time means with higher reproductive indices. 



The influence of general environmental factors is seen in the 

 somewhat coincident up-and-down movements of the curves for the 

 two strains. 



Line 691. 



The data for Line 691 are presented in tables 13 and 14 and in 

 figure 4. This is one of the original lines of D. pulex. Selection was 

 begun in the seventh generation and continued for 87 and 89 genera- 

 tions in the two strains. The experiment was terminated by the 

 loss of the plus strain after 27 months of selection. 



For the first 4 months of the experiment the mean reaction- 

 times for the plus and minus strains (only 40 and 35 individuals 

 respectively) were 480.9 and 434.9 seconds (table 13). The plus 



