PHYSICAL CHARACTERS IX MAN 



47 



TABLE II. 

 Mother Blue x Father Browx. 



Clearly from the tables, when the father has brown 

 eyes, half the sons have blue e3"es and half brown, 

 but many more daughters have brown than blue 

 eyes, although the total numbers of the sexes are 

 equal. On the other hand, when the mother has 

 brown eyes there is a marked excess of blue-eyed sons 

 and daughters. After an elaborate analysis these 

 results are explained by assuming that in addition 

 to the simple pair of factors originally recognised, 

 there is another dominant factor for brown eyes 

 which is sex-linked in inheritance. The writer is 

 further obliged to assume that female germ cells 

 (b W) containing the sex-linked factor (W) together 

 with the ordinary determiner for blue, cannot exist. 

 It should not be difficult to obtain extensive data of 

 eye colour to test these h3'potheses. All the assump- 

 tions made are reasonable enough in the light of 



