xii CONTENTS 



PAGE 



A factor system in stocks 166 



Truncate winged Drosophila 168 



The factor explanation of reversion 170 



Darwin's hybridization experiments with pigeons 171 



Factor analysis of plumage color in pigeons 172 



CHAPTER X 

 FACTOR RELATIONS IN QUANTITATIVE INHERITANCE 



Introductory 174 



Meaning of quantitative inheritance , . . 174 



Tall and dwarf races 174 



Bush and cupid sweet peas 175 



Other factor differences affecting size 177 



The cotton leaf factor 179 



Corolla length in tobacco 181 



Mathematical requirements of the multiple factor theory of size inheritance . . . 185 



Castle's hooded rats 186 



Hypothesis of factor variability 192 



Arguments for the multiple factor theory 194 



CHAPTER XI 

 INHERITANCE OF SEX AND RELATED PHENOMENA 



Introductory 196 



The Drosophila or XY type of sex-inheritance . . ' 196 



Sex-linked inheritance 197 



Non-disjunction in Drosophila 198 



Secondary non-disjunction 201 



Non-disjunction not due to a sex-linked factor 204 



Bearing of non-disjunction on chromosome constitution of sex 204 



The WZ type of sex-inheritance 205 



Analogy between the two types 209 



Sex-determination in certain insects 210 



Sex-determination in certain plants 212 



Secondary sexual characters 214 



The question of sex factors 215 



Intersexual forms in Lymantria 216 



Analogous case in tobacco 218 



Conclusion 218 



CHAPTER XII 

 SPECIES HYBRIDIZATION 



Introductory 219 



Genetic compared with taxonomic differences 219 



Species hybrids in Antirrhinum 220 



Species hybrids in Cavia 223 



