CONTENTS. 



Page 



General statement 5 



Source of material 6 



Culture methods 8 



Pedigree records 11 



Method of selection 13 



General procedure 13 



Environmental influences and reaction- 

 time 17 



Test series 18 



Same-day broods 19 



Possible criticisms of methods of selec- 

 tion 20 



Nature of swimming movements of Cla- 



docera species used in selection . 24 

 Behavior of young of the different species 

 when released in the experimen- 

 tal tank 24 



Relation between environmental condi- 

 tions and reproductive age 26 



Statistical treatment of data 26 



Analysis of data 28 



Line 695 28 



Presentation of data 28 



Analysis of data for effect of selection 38 

 Relation between reproductive vigor 



and reactiveness to light 40 



Line 689 46 



Line 691 49 



Line 711 51 



Line 713 55 



Line 714 56 



Line 719 60 



Line 751 66 



Line 762 68 



Line 766 70 



Line 768 70 



General introduction for Simocephalus 



exspinoaus lines 73 



Line 794 74 



Line 795 77 



Line 796 80 



Line 740 84 



Line 757 89 



Presentation of data 89 



Detailed analysis of data for Line 757 97 

 Reaction-time means compared by 



longer periods 97 



Other features of the data 104 



Relation between relative vigor and 



mean reaction-time 108 



Page 

 Analysis of data — Continued. 

 Line 757 — Continued. 



Special features of the reaction-time 



curves 115 



Extent of the change in reactiveness 



of the Line 757 plus strain 116 



Reactiveness of both strains of Line 



757 modified through selection. 118 

 Conclusion regarding effect of selection 



in Line 757 126 



Environmental conditions as affecting 



reaction-time and vigor of stock 128 



1. Temperature influences 128 



2. Influence of substances exhaled from 



observer's breath 130 



3. Relatively temporary chemical (?) 



differences in water used in ex- 

 perimental tank 131 



4. Occurrence of negatively reacting 



individuals 132 



5. General influences operative through 



longer periods of time 132 



Coincident changes in reactiveness . . 133 

 Seasonal changes in reactiveness. . . 135 

 Contemporaneous shifts in reaction- 

 time means 135 



General increase in reactiveness of 



Simocephalus exspinosus 137 



Independent shifts in reaction-time 



means 140 



Whether " depression periods " occur. 142 



6. Environmental conditions as affect- 



ing vigor of stock 143 



Reliability of the reproductive index. 143 

 Coincident fluctuations in vigor .... ] 44 

 Independent fluctuations in vigor. . . 145 

 Differences between reproductive 

 indices during different parts of 



experiment 146 



Is the increased reactiveness for lines 

 of Simocephalus exspinosus asso- 

 ciated with increased vigor? .... 147 

 Possible divergence in vigor between 

 the two strains of a selected line 148 



Statement of results of selection 150 



Discussion of results 152 



Summary 163 



References 169 



