CONTENTS xiii 



CHAPTEK PAGE 



5. Potency .179 



a. Total potency 179 



6. 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 



b. 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 

 j~j 3. Experiments in human heredity .... 227 



a. The Jukes 227 



6. 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 



