THEORY OF EVOLUTION 55 



sic case of the combs of fowls. If a bird with a 

 rose comb is bred to one with a pea comb (fig. 

 23), the offspring have a comb different from 

 either. It is called a walnut comb. If two 

 such individuals are bred they give 9 walnut, 



FIG. 23. Cross between pea and rose combed fowls. (Charts 

 of Baur and Goldschmidt.) 



3 rose, 3 pea, 1 single. This proportion shows 

 that the grandparental types differed in re- 

 spect to two pairs of characters. 



A fourth case is shown in the fruit fly, where 

 an ebony fly with long wings is mated to a grey 

 fly with vestigial wings (fig. 24). The off- 



