44 THE METHODS AND 



encouraging fact. If we are right, as I am 

 strongly inclined to believe, we get a glimpse 

 of the significance of the popular idea that in 

 certain respects daughters are apt to resemble 

 their fathers and sons their mothers ; a phe- 

 nomenon which is certainly sometimes to be 

 observed. 



There are several collateral indications 

 that we are on the right track in our theory 

 of the nature of sex. One of these, derived 

 from the peculiar inheritance of colour- 

 blindness, is especially interesting. That 

 affection, is common in men, rare in women. 

 Men who are colour-blind can transmit the 

 affection, but men who have normal vision 

 cannot. Women however who are ostensibly 

 normal may have colour-blind sons; and 

 women who are colour-blind have, so far as 

 we know, no sons who are not colour-blind 1 . 



1 We have knowledge now of seven colour-blind women, 

 having, in all, 17 sons who are all colour-blind. Most of these 

 cases have been collected by Mr Nettleship. 



