CONTENTS Xlll 



2. hi Crosses between Species 188 



3. In Mutant Races 193 



4. In Tetraploid Races 194 



Identity of Distribution of the X-chromosomes and of 8ex-linked 



Factors -r, 19^ 



1. In Ordinary Crosses <Jr7 195 



2. In Cases of Non-disjunction 196 



CHAPTER VIII 

 MULTIPLE ALLELOMORPHS 



Definition of Multiple Allelomorphs 202 



Examples of Multiple Allelomorphs 202 



The Alternative Interpretations of Identical Loci and Complete 



Linkage 204 



CHAPTER IX 



MULTIPLE FACTORS ' 



The Meaning of the Term "Multiple Factors" 21 



Examples of Multiple Factor 219 



Selection and Multij)le Factors 248 



CHAPTER X 



THE FACTORIAL HYPOTHESIS 



On the Relation between Factors and Characters 262 



1. The Organi>^in-as-a-Whole Objection 265 



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



Character 266 



3. So-called Contamination of Allelomorphs 268 



4. Fractionatif)n 268 



5. The Presenc(> and Absence Hj'pothesis 270 



Weismann's Preformation Hypothesis and the Factorial Theory . 277 



C?IAPTER XI 



VARIATION IN THE PROTOZOA 



Fission Linos 282 



C'hange in XuiTibcr of Nuclei 291 



