CHAPTER IV. 



The Determination of Sex. 

 {Experiment and Rationale.^ 



§ I. Influence of Nutrition. — Throughout nature the influence 

 of food is undoubtedly one of the most important environ- 

 mental factors. To Claude Bernard, indeed, the whole problem 

 of evolution was very much a question of variations of nutrition. 

 " L'evolution, c'est I'ensemble constant de ces alternatives de 

 la nutrition ; c'est la nutrition consideree dans sa realite, em- 

 brassee d'un coup d'oeil a travers le temps." It is fitting that 

 we should begin our survey of the factors known to influence 

 sex with the fundamental function of nutrition. 



{a) The Case of Tadpoles. — Not a few investigators who 

 have passed from statistics and hypothesis to experiment and 

 induction, have found their material in tadpoles, where the sex 

 seems to remain for a comparatively long period indeterminate. 

 If we take the verdict of Yung, who has had most experience 

 with these forms, tadpoles pass through a hermaphrodite stage, 

 in common, according to other authorities, with most animals. 

 During this phase external influences, and especially food, decide 

 their fate as regards sex, though the hermaphroditism, as we 

 shall afterwards see, sometimes persists in adult life. It is fair, 

 however, to notice that Pfliiger gives a somewhat different 

 account of the actual facts, distinguishing among tadpoles three 

 varieties — (a) distinct males, {b) distinct females, and {c) herma- 

 phrodites. In the last, testes, or male organs, develop round 

 primitive ovaries, and if the tadpoles are to become males the 

 enclosed female organs are absorbed. 



Adopting the view stated by Yung, we shall simply state the 

 striking results of one series of observations. When the tadpoles 

 were left to themselves, the percentage of females was rather in 

 the majority. In three lots, the proportions of females to 

 males were as follows : — 54 : 46 ; 61 : 39 ; and 56 : 44. The 

 average number of females was thus about 57 in the hundred. 



