482 



HEREDITY AND SEX 



simple creatures like starfish and sea-urchins, where it often 

 requires a microscopic examination before we can be sure whether 



Fig. 45. — Decorative male and less adorned female of Spathura — a genus 

 of Humming-birds. (From Darwin, after Brehm.) 



we are dealing with a male or a female organism. The primary 

 difference between the sexes is that between egg-production 



