A PHYSIOLOGICAL CHARACTER. 65 



strain of Line 719 continued more reactive than the combined means 

 of the other lines for 10 months, but the differences were small and 

 not of statistical value. For the remaining 7 months of the curve the 

 differences were variable and the mean for the plus strain did not 

 differ appreciably from the composite curve of means for the corre- 

 sponding plus strains. 



The evidence seems suggestive of a mutation in the minus strain 

 of Line 719, rendering it the more reactive to light. Since the differ- 

 ence between the mean for the minus strain of Line 719 and the plus 

 strain of the same line, as well as between the Line 719 minus strain 

 and the combined means for the minus strains of the lines, which 

 may fairly serve as checks, later decreased and was apparently 

 practically lost, it seems probable that selection served to reduce or 

 eliminate the effect of this apparent mutation. 



This reduction in (or possible elimination of) the reaction-time 

 difference in Line 719 is worthy of consideration as contrasted with 

 Line 757, in which the difference in reaction-time (which in that 

 case is in the direction attempted in selection) became larger and 

 larger in successive year-periods, until, instead of being a difference 

 of 5.5 per cent, as in the last period of selection in Line 719, it was 

 99 per cent in the last year-period for Line 757. 



Line 719 affords a case parallel to that of Line 689, in which the 

 plus strain likewise persistently had a higher reaction-time, contrary 

 to any influence of selection. With Line 689 the period of the experi- 

 ment was much shorter, but otherwise the results are very similar, 

 except that in Line 719 the difference is not so large or so uniform, 

 is not supported by most of the same-day-brood data, and became 

 much smaller during the latter part of the experiment. 



It is to be noted with Line 719 that in reproductive vigor the 

 minus strain was in general inferior to the plus strain. This was 

 markedly true during the first and the last year-periods. The minus 

 strain was slightly superior in vigor during the second year-period. 

 Yet the minus strain was the more reactive throughout all these 

 year-periods and was (absolutely) somewhat less reactive during its 

 year of superior vigor (August 1913-July 1914) than during the other 



two years. 



The curves for the mean reaction-times by two-month periods 

 (figure 8c) indicate an interesting correlation between the means for 

 the two strains, the plus and minus curves, in spite of their fluctua- 

 tions, following each other remarkably closely. This is again an 

 expression of environmental effect. The small and variable, though 

 fairly pronounced, superiority in reactiveness on the part of the 

 minus strain for most of the period of selection is rendered even more 

 interesting by the fact that the differences persist while the curves 

 sweep up and down under environmental influences. 



