CHAPTER XVII 



SEX DETERMINATION AND SEX DIFFERENTIATION 



Introductory statement. — In chapter xiv we have spoken of sexual 

 reproduction as one of the modes of cytogenic reproduction. We have 

 also referred several times to the ways in which sexual reproduction 

 constitutes the main mechanism of diversity. Two questions with 

 regard to sex, however, have not yet been broached: (a) What de- 

 termines the sex of the individual? (b) How do the secondary sexual 

 characters of individuals develop? These two questions will be an- 

 swered in the present chapter. 



SEX DETERMINATION 



The question as to what determines whether an animal shall be a 

 male or a female is a very ancient one, and it is only during the present 

 century that we have solved the puzzle. 



A great many theories of sex determination have been proposed, 

 some of which are as follows : 



a) Hippocrates and some subsequent theorists believed that the 

 sex of the offspring depended on the relative vigor of the parents, the 

 more vigorous parent giving his or her sex to the offspring. 



b) Thury thought that the sex of the offspring depended on the 

 degree of ripeness of the ovum at the time of fertilization. 



c) Various writers claim that statistics show that germ cells from 

 the right ovary produce males and those from the' left ovary females. 



d) The nutrition theory. — The egg is a much more highly nourished 

 cell than the spermatozoon, and the idea seems natural that high 

 degrees of nourishment of the mother produce female offspring and 

 lower degrees of nourishment male offspring. Professor Schenk of 

 Vienna gained a huge reputation by controlling the diet of certain 

 royal prospective mothers and predicting the sex of the offspring 

 accordingly. He was correct in his predictions several times, but his 

 success was short-lived. His early predictions were merely lucky, 

 just as one might be who could guess heads or tails correctly several 

 times in succession. 



Some color is lent to the nutrition hypothesis by the fact, if it is a 

 fact, that after war or famine, when the nutrition of mothers has been 



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