. Carnegie Institution of Washington publication. A PHYSIOLOGICAL CHARACTER. 53 This is one of the original lines of D. pulex obtained from Pond II, the spring-fed pond in the woods, during November 1911. Se- lection was begun in the sixth laboratory generation and continued for 15 months, for 45 generations in the plus and 46 generations in the minus strains. For the first 4 months of the experiment with this line the means were, for the plus strain seconds (52 individuals) and for the minus strain seconds (49 individuals). The difference ( — ± seconds) was times the
. Carnegie Institution of Washington publication. A PHYSIOLOGICAL CHARACTER. 53 This is one of the original lines of D. pulex obtained from Pond II, the spring-fed pond in the woods, during November 1911. Se- lection was begun in the sixth laboratory generation and continued for 15 months, for 45 generations in the plus and 46 generations in the minus strains. For the first 4 months of the experiment with this line the means were, for the plus strain seconds (52 individuals) and for the minus strain seconds (49 individuals). The difference ( — ± seconds) was times the probable error (table 17). The mean reaction-time for the plus strain for the first two-month period was 244 seconds less than that for the minus strain, but for the second two-month period the minus strain had the lower reaction- time by 63 seconds (tables 15 and 16). There were 3 same-day broods, for which those of the plus strain had a higher mean reaction-time by 42 seconds (table 18). The data for this first 4 months of selection are not as satisfactory as that obtained later and wide fluctuations are less sur- prising. For the remaining year (nearly) of the experiment with this line, the mean for the plus strain was seconds (235 individuals); that for the minus strain was seconds (190 individuals). The same-day broods, of which there were 6, have means differing by only — 7 seconds. Exam- ination of the data (tables 15 and 16) and the curves (figure 5) for this line shows consistent differences in mean reaction-times during this year-period. The wide divergence in mean reaction-times for August-September is a chance result due to there being extremely few tested individuals during this period. But for the following 5 two-month periods the numbers of tested individuals were greater and the rather uniform courses of the curves are sugges- tive of a difference due to selection. Comparison of the curves for the means of the two strains of this line with the c
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