A PHYSIOLOGICAL CHARACTER. 141 



1912-October 1913, when in general the plus curve was low (see 

 figures 6 and 10o); December 1913-July 1914, when the plus curve 

 was relatively high; and October 1914-July 1915, when the plus 

 curve again was relatively low, compared in each case with the com- 

 posite curve (figure lOo). The minus curve fluctuated similarly, but 

 to a less degree. 



In Line 714 the minus curve shows 3 parts where it is quite 

 separated from the plus curve (figure 7c) : (1) April-September 1912, 

 when it is high; (2) June-September 1913, when it was low; April- 

 July 1914, when it was high. None of these cases has apparent 

 genetic significance. 



Line 794 shows (figure lie) 2 fluctuations, each consisting of 3 

 two-month periods. During the first (December 1914-May 1915) 

 the minus strain was low, and during the second (June-November 

 1915) it was high, both relative to the plus strain of Line 794 and the 

 composite curves for the other S. exspinosus strains (figure 18s). 



Line 795 shows two similar periods for the minus strain (figure 

 12c): February-May 1915 and December 1915-July 1916, during 

 which this strain was lower relative to the plus strain of this line and 

 the composite curves for the other S. exspinosus strains (figure 18s). 



Line 740 shows 3 periods of 6, 10, and 10 months, during which 

 the two strains differed consistently in reaction-time. The first 2 

 periods, February 1914-July 1914 and September 1914-May 1915, 

 are apparently due principally to fluctuations in the plus strain. 

 There were no sufficient other strains of this species in the laboratory 

 during this time to make adequate comparisons. During a third 

 period, April 191 6- January 1917, the minus strain ran higher than 

 the composite curve for the other minus strains (except Line 757, see 

 figure 18s). For the latter part of this period the plus strain of Line 

 740 ran abnormally low. The two fluctuations produced a relatively 

 large difference between the reaction-time curves for the two strains 

 of this line. The later history of the two strains, especially the 

 test-series data obtained at the close of selection with this line, indi- 

 cated that this divergence had no genetic basis. 



Line 757 shows a period, June 1914-July 1915, in which 4 of the 

 7 two-month periods show relatively low points in the curve for Line 

 757 minus (figure 18s). While the effect of selection within this line 

 is such that the minus curve drops below the plus curve at only one 

 point, it is believed this clearly represents a period, or two periods 

 (the October 1914-January 1915 period shows the minus curve rela- 

 tively high), which are in every way similar to these just referred to 

 (for the other lines) and that non-genetic influences served to mask 

 the effects of selection during this portion of the experiment. 



The outstanding fact regarding local fluctuations in reaction- 

 time means of the two strains in Line 757 is that they produce 

 relatively so little reduction or interruption of the difference between 



