Sex as an Adaptation Azz 
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 réle. 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 
