Sex as an Adaptation 423 



then the evidence pointing in the opposite direction. Among 

 the different causes suggested as determining the sex of the 

 embryo, that of the condition of the egg itself at the time of 

 fertilization has been imagined to be an important factor in 

 the result. Another similar view holds that the condition of 

 the spermatozoon plays the same role. For instance, it has 

 been suggested that if the egg is fertilized soon after it leaves 

 the ovary, it produces a female, but if the fertilization is de- 

 layed, a male is produced. It has also been suggested that 

 the relative age of the male and the female parents produces 

 an effect in determining the sex of the young. There is 

 no satisfactory evidence, however, showing that this is really 

 the case. 



Another view suggested is that the sex is determined by 

 the more vigorous parent ; but again there is no proof that 

 this is the case, and it would be a difficult point to establish, 

 since as Geddes and Thompson point out, what is meant by 

 greater vigor is capable of many interpretations. Some- 

 what similar is the idea that if the conditions are favorable, 

 the embryo develops further, as it were, and becomes a 

 male ; but there are several facts indicating that this view 

 is untenable. 



Diising maintains that several of these factors may play a 

 part in determining the sex of the embryo, and if this be true, 

 the problem becomes a very complex one. He also suggests 

 that there are self-regulative influences of such a kind that, 

 when one sex becomes less numerous, the conditions imposed 

 in consequence on the other sex are such as to bring the 

 number back to the normal condition ; but this idea is far 

 from being established. The fact that in some species there 

 are generally more individuals of one sex than of the other 

 shows that this balance is not equally adjusted in such forms. 



Of far greater value than these speculations as to the origin 

 of sex are the experiments that appear to show that nutrition 

 is an important factor in determining sex. Some of the 



