CHROMOSOMES, HEREDITY xVND SEX. 
515 
between the sexes, and that, when estimated by precipitin 
tests, there is nearly as much difference between the blood of 
the male and female of one species as between tlie bloods of 
the same sex of related species. Such observations as these, 
taken together with the fact that the secondary sexual 
characters of each sex can be inherited through the other 
sex ( 61 ), suggest that possibly the fundamental difference 
between the sexes is not a factor which directly determines 
whether the individual shall possess testes or ovaries, but 
is really a difference of metabolism. 
Where differences of metabolism ai-e found in the two sexes 
it has usually been assumed that these are caused by the 
presence of testes or ovaries, by means of hormones or other 
internal secretions. It may, however, he worth while to con- 
sider whether the metabolic differences are not primary, and 
whether the primitive gonad may not develop into an ovary in 
one case and a testis in the other in consequence of a funda- 
mental difference existing in all the cells. In vertebrates the 
secondary sexual differences are largely dependent on the 
presence of a functional ovary or testis, but in insects this is not 
the case, and if Steche’s observations are substantiated they 
indicate that all the cells of the body are different in the two 
sexes. Further, the existence of occasional gynandromorphs in 
vertebrates, in which one side of the body has male characters, 
the other female, while the gonad contains both male and 
female elements, shows that there must be some difference in 
the tissues of the two sides of the body on which the secre- 
tion of the gonad can act.^ If, then, there is any truth in 
the conception here outlined, the presence or absence of a 
chromosome does not affect the primary sexual organs 
directly, but, perhaps by its presence in every cell, alters the 
whole metabolism in such a way that the organism is caused 
to become of one sex rather than of the other, in consequence 
of its type of metabolism. There is no necessary reason, 
however, for supposing that other causes might not alter the 
metabolism in the same way. Geoffrey Smith has, in fact, 
^ This was pointed out by C. J. Bond at the British Association, 1913. 
