CHAPTER XIII 



HEREDITY AND SEX 



"Sex lies deeper than culture." — Maudsley 



§ I. The Problem of the Determination of Sex 



§ 2. Variety of Possible Factors in Sex-Determina ion 



§ 3. Alleged Determining Influence of External Factors 



§ 4. Influence of the Parents 



§ 5. Internal Conditions 



§ 6. ^ Statistical Investigation 



§ 7. Inconclusive Conclusions 



§ I. The Problem of the Determination of Sex 



The Problem. — Much interest has always been excited by 

 the question : What determines the sex of the offspring ? The 

 fertihsed ovum will develop into a cock or a hen, into a bull or 

 a cow, into a horse or a mare, into a man or a woman, and it is 

 obviously of practical as well as theoretical interest to inquire 

 what determines the sex of the offspring. What are called 

 " true twins " in the human race, which appear to result from 

 the division of an ovum into two, are always of the same sex ; 

 but ordinary twins, which result from two ova developing simul- 

 taneously, are often of different sexes. What determines this ? 

 In one household all the children are boys, next door they are 

 aL girls, in most cases there are both boys and girls : what de- 

 termmes this ? The eggs of a bird's clutch develop into males and 

 tema.es in varying proportions, but in one case at least it has 



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