HEREDITY AND SEX 



tions upon guinea-pigs extending over a series 

 of years. Oftentimes I found an individual 

 that produced more offspring of one sex than 

 of the other, but this was probably due merely 

 to chance deviations from equality. I could 

 get no evidence that the condition was inher- 

 ited, though the experiment was continued 

 through as many as seven generations, includ- 

 ing several hundred offspring. 



The essential difference between a female 

 and a male individual is that one produces 

 eggs, the other sperm. All other differences 

 are secondary and dependent largely upon the 

 differences mentioned. If in the higher ani- 

 mals (birds and mammals) the sex-glands (i. e. 

 the egg-producing and sperm-producing tis- 

 sues) are removed from the body, the super- 

 ficial differences between the sexes largely dis- 

 appear. In insects, however, the secondary 

 sex-characters seem to be for the most part 

 uninfluenced by presence or absence of the 

 sex-glands. Their differentiation occurs in- 

 dependently though simultaneously with that 

 of the sex-glands. 



The egg or larger gamete (the so-called 

 155 



