• • • 



CONTENTS Xlll 



CHAPTER VIII 

 MULTIPLE FACTORS 



PAGE 



The Meaning of the term " Multiple Factors " 172 



Examples of Multiple Factors 172 



Selection and Multiple Factors 195 



CHAPTER IX 

 THE FACTORIAL HYPOTHESIS 



On the Relation between Factors and Characters 208 



1. The Organism-as-a- Whole Objection 211 



2. The Invariability of the Factor and the Variability in the 



Character 212 



3. So-called Contamination of Allelomorphs . . . . . . .214 



4. Fractionation 214 



5. The Presence and Absence Hypothesis 216 



Weismann's Praeformation Hypothesis and the Factorial Theory ." 223 



APPENDIX 



Methods of Breeding Drosophila 229 



Acknowledgments 235 



Bibliography 237 



Index 259 



