HEREDITY 



black, whereas the eyes of the albino are pink. 

 If such a black-eyed white guinea-pig is crossed 

 with an albino of the sort shown in Fig. 15, 

 the young produced will be black all over. 

 Now this result shows that the black-eyed 

 white animal possesses what is lacking in the 

 albino as compared with the all-black animal. 

 It would seem, therefore, that it lacks some- 

 thing different from what the albino lacks, and 

 that a cross of the two supplies both lacks, the 

 albino supplying what is wanting in the black- 

 eyed white, and vice versa. Accordingly, wholly 

 black offspring result from the crossing of the 

 two white races. 



But the case of white poultry is different 

 from this, since white poultry lack nothing 

 that is necessary to produce the complete 

 black plumage. For when white fowls crossed 

 with black ones produce white offspring, if 

 these offspring are then bred with each other, 

 they produce both white offspring and black 

 ones in the ratio 3 to 1. White fowls, there- 

 fore, are able to produce the black condition. 

 This ability is in the white individual held in 

 abeyance, it is not exercised. Why, we do 



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