A PHYSIOLOGICAL CHARACTER. 45 



action-time during 14 of these periods, while in 12 two-month periods 

 the more vigorous strain had the higher reaction-time. For one 

 period the average reaction- times were equal. Compared by periods 

 of a single month, the strain having the greater vigor had a lower 

 reaction-time in 23 cases and a higher reaction-time in 26 cases. 

 For one month the vigor of the two strains measured the same, for 

 one month the reaction-time was the same, and for three months the 

 data were incomplete and a comparison could not be made. 



Hence in the selection experiment with Line 695 no relation 

 is discovered between fluctuations in general vigor and mean re- 

 action-time, either when the data are examined month by month or 

 by longer periods during which there was a constant difference in 

 reaction-time. Whether the measure of vigor is taken as the rate 

 of descent or as the reproductive index, any reaction-time differ- 

 ences which one might have expected to find explicable on the basis 

 of differences in vigor between the two strains quite fail to appear so. 



The test series may again be referred to. Three of the four of 

 these gave differences in mean reaction-time which are statistically 

 significant; 1 for one the difference was practically nil. Of the three 

 differences of statistical significance, two were differences in which, 

 in opposition to selection, the plus strain had the higher reaction- 

 time and only one of the differences was in the direction of selection. 

 Hence their net effect is to indicate a lack of effect of selection. 



Examined as a whole and on the points considered in detail, it 

 is obvious that with Line 695 there was no effect of selection. This 

 is by no means surprising, for if an effect of selection is obtainable 

 with a given material it is not to be expected that such effect will 

 necessarily be secured every time it is attempted. Selection can- 

 not be effective unless germinal variation occurs which affects the 

 character used as a basis for selection; and there seems no logical 

 reason for supposing that germinal variation occurs in all, or to the 

 same extent, or at the same time, in all material which is otherwise 

 apparently entirely similar. 



It would be superfluous to make such an extended analysis of 

 the data for each of the lines as has been attempted for Line 695. 

 Tables of data and diagrams similar to those for Line 695 are given 

 for all the lines (though some of these lines have their data presented 

 somewhat less fully), but it has not seemed necessary to make the 

 treatment nearly so complete. The tabulated summaries and the 

 curves plotting reaction-times and the reproductive indices render 

 the interpretation rather obvious after the full treatment accorded 

 Line 695. Of the other lines, the data for Line 757 alone are examined 

 rather extensively because of the interesting result within that line. 



1 The times at which these test series were conducted are indicated by the roman numerals 

 on figure 2c. 



