CONTENTS xiii 



HAPTEB PAGE 



5. Potency * , .179 



a. Total potency . ', . 179 



b. Partial potency 180 



c. Failure of potency 180 



6. Blending inheritance 182 



7. The case of rabbit ears 183 



8. The Nilsson-Ehle discovery 186 



9. The application of Nilsson-Ehle's explanation to the 



case of rabbit ear-length .... 193 



10. Human skin color 196 



X. THE DETERMINATION OF SEX. 



1. Speculations, ancient and modern .... 197 



2. The nutrition theory 198 



3. The statistical study of sex 200 



4. Monochorial twins 201 



5. Selective fertilization 202 



6. The neo-Mendelian theory of sex .... 205 



a. Microscopical evidence 207 



1. The " x " chromosome .... 207 



2. Various forms of x chromosomes . . 208 



3. Sex chromosomes in parthenogenesis . 210 

 6. Castration and regeneration experiments . . 210 



c. Sex-limited inheritance 213 



1. Color-blindness 214 



2. The English currant-moth . . .216 



d. Behavior of hermaphrodites in heredity . . 220 



7. Conclusion 222 



XI. THE APPLICATION TO MAN. 



1. The application of genetics to man .... 224 



2. Modifying factors in the case of man . . . 225 



3. Experiments in human heredity .... 227 



a. The Jukes 227 



b. The descendants of Jonathan Edwards . . 228 



c. The Kallikak family 229 



4. Moral and mental characters behave like physical 



ones 230 



5. The character of human traits 231 



6. Hereditary defects 232 



