82 



SELECTION IN CLADOCERA ON THE BASIS OF 



For the second longer period the reaction-time means were 

 619.1 and 697.5 seconds. The difference was —78.4 ±14.7 seconds, 

 5.33 times the probable error. The 10 same-day broods gave averages 

 differing by only —6 ±24.07 seconds. 



The data for the last longer period (August 1916 to the end of 

 the selection experiment in April 1917) gave as means 449.4 and 



2.00 



1.50 



1.00 



.50 



i 



I 



T J 



750 - 



600 



450 - 



300- 



150 - 



Figure 13. — Line 796. 



A. Reproductive indices, actual values. 



B. Reproductive indices, superiority. 



C. Reaction-time curves. (The asterisk indicates a point 



established from insufficient data, only one brood.) 



393.7 seconds. The minus strain was the more reactive by 55.7 ±19.1 

 seconds, 2.92 times the probable error. The same-day-brood 

 means (only 4 broods of each strain) differed by 220 seconds, the 

 minus strain being the more reactive. A test series conducted during 

 August 1916 consisted of 662 and 643 individuals in the two strains. 



