A PHYSIOLOGICAL CHARACTER. 167 



26. In the short experiment with Line 766 (derived from Line 

 762) there was no effect of selection. 



27. There was no effect of selection in Line 768. 



28. Most of the data for Line 794 suggest an effect of selection, 

 though the test series did not support this conclusion and effect of 

 selection must remain in doubt. 



29. Effect of selection is strongly indicated for the final data 

 for Line 795, but in view of the earlier differences in the opposite 

 direction and the small amount of the data which indicate an effect 

 of selection, the result is questionable. 



30. There is clearly no effect of selection in Line 796. 



31. Certain portions of the data for Line 740 seem to indicate 

 consistent differences in reaction-time for the two strains. A possible 

 mutation early in the course of the experiment was examined, but 

 ruled out as improbable. For 14 months preceding the final 3 

 months of the experiment, the plus strain was somewhat more 

 reactive. However, the data for the final 3 months of the experiment, 

 together with a large test series, indicate a lack of selective effect. 



32. A large effect of selection is clearly indicated for Line 757: 

 (a) This conclusion is consistently attested by every check 



which was applied to the data. 



(6) The effect was due both to an increased reactiveness of the 

 plus strain and a reduced reactiveness in the minus strain 

 (relatively to the other plus and minus strains of Simo- 

 cephalus) . . 



(c) The divergence between mean reaction-times became large. 



(d) The divergence in reactiveness was permanent, or, at any 

 rate, still existed 32 months (112 generations) after selection 

 was discontinued. 



(e) Except for the difference in reactiveness to light, and a 



slightly lower reproductive index (which was not in evidence 

 during the latter part of the experiment) in the minus 

 strain, there is nothing to distinguish the two strains. 



33. It is not believed that general physiological differences or 

 cytoplasmic transmission can be appealed to as explaining the result, 

 particularly in view of the apparently permanent nature of the 

 changes in reactiveness. 



34. The effect is presumably not due to genetic segregation 

 (unless there is assumed a novel method of segregation, for which 

 there is no evidence) inasmuch as at least three such segregations 

 seem necessary to explain the result on this basis and there is no 

 chromatic reduction in the maturation of parthenogenetic eggs of 

 Cladocera. 



35. A possible novel method of segregation is suggested. Such 

 an assumption would explain the results with Line 757 in accord with 



