166 SELECTION IN CLADOCERA ON THE BASIS OF 



14. The data for the over-time individuals presented a serious 

 difficulty. In many cases, especially with the Siinocephalus lines, 

 they constituted a considerable portion, and a most significant por- 

 tion, of the reaction-time data. Over-time individuals were arbi- 

 trarily assigned a reaction-time of 900 seconds and treated as though 

 they had reached an end of the tank within the period of the test. 

 This expedient really minimized the rightful influence of these 

 relatively slightly reactive but highly significant individuals. 



15. Negatively reacting individuals were very irregular in occur- 

 rence and of doubtful significance. They were utilized in selection in 

 the minus strains under the assumption that a genetic change might 

 occur rendering an individual fundamentally negative in its reactions 

 to light. 



16. Many of the data are published for the benefit of workers 

 who might wish to go over the analysis or make further analysis. 



In the treatment of the data for the different lines the following 

 results are recorded: 



17. For Line 695 there was not an effect of selection. A marked 

 general influence of environmental factors upon reaction- times is 

 observed, as is true with most of the other lines. 



18. In Line 689 selection was not effective. On the contrary, 

 there was a persistent, though slight, difference tending to indicate 

 that the minus strain was the more reactive. 



19. In Line 691 there was no certain effect of selection, though 

 part of the data suggests such an effect. 



20. In Line 711 a selective effect is strongly suggested, though 

 not fully supported by the same-day-brood data. The evidence for a 

 genetic difference between the two strains is, however, as good or 

 better than that suggesting a genetic difference between the two 

 strains of Line 689. 



21. The data in part suggest an effect of selection in Line 713, 

 but it is improbable that such actually occurred. 



22. Some of the early data for Line 714 suggest an effect of 

 selection, but the later data show clearly that such had not occurred. 



23. In Line 719, as in Line 689, there is a generally higher 

 reaction-time for the plus strain. The different periods of the data, 

 in spite of considerable fluctuations, rather consistently bear out this 

 interpretation, and genetic differences in opposition to selection are 

 believed to have arisen. Selection possibly operated to reduce this 

 difference, which was less marked during the latter part of the 

 experiment. 



24. There was no effect of selection in Line 751. 



25. Some of the final data for Line 762 suggest an effect of 

 selection, but the data are not sufficient to be at all convincing. 



