92 THE REPRODUCTION AND LIFE-HISTORY OF ANIMALS 



colour appearing. But if the black guinea-pigs of the Fg 

 generation are inbred, a fraction of their offspring will be 

 white. Further examination will show that the F2 genera- 

 tion of guinea-pigs, with their three-to-one ratio of black 

 to white, is more comparable than appears at first sight 

 to the F2 generation of the Andalusian fowls, with their 

 one-two-one ratio of black, blue, and white. For if the 

 blue Andalusian fowls happened to be more like the black 

 ones than they are, so like that they could not be distin- 

 guished, then it would not be possible, except by chance, 

 to inbreed the pure blacks of the Fg generation and obtain 

 only pure black offspring ; one would be more likely to 

 have chosen one or two of the indistinguishable mixed 

 forms, and a fraction of the offspring would be white. 

 Thus it appears that of the black guinea-pigs of the Fg 

 generation one-third are " pure " black, and if by chance 

 these can be inbred, their offspring will all be black; but 

 two-thirds of the Fg black guinea-pigs are in reality mixed 

 forms, and if two of them can be bred together, their 

 offspring will be blacks and whites again in the ratio 

 three-to-one. But the pure blacks and the mixed blacks 

 are indistinguishable in appearance, and only by lengthy 

 breeding experiments can the one be told from the other. 

 The matter may be made clearer by a diagram, in which 

 " D " represents the dominant character and " R " the 

 recessive, which is completely masked in the presence 

 of the dominant. 



P generation D x R 



Fi generation /D(R) \ 



V \ 



F2 generation D D(R) D(R) R 



/ ■ ^ \ 



D D D(R) D(R) R R 



To explain these results it is suggested that the mixed 

 forms of the F^ generation receive a " factor " for blackness 

 from the one parent, a factor for whiteness from the other, 

 though the presence of the latter is masked. But the 

 recessive factor remains present, and the germ-cells of the 



