222 



EVOLUTION, GENETICS, AND EUGENICS 



shall be a male or a female, and in addition we have explained why 

 equal numbers of both sexes are continuously produced. 



How general is the chromosomal mechanism of sex-determina- 



Fig. 53. — Diagram showing chromosome relations in the determination of sex 

 in Drosopliila ampelopliila. {From Babcock and Clausen.) 



tion? — "To what extent," says E. B. Wilson, "sex may be determined 

 by an automatically operating nuclear mechanism such as has been 

 here described is unknown; but a mechanism that exists in the same 



