HEEEDITY 



each parent is different it can be shown 

 that the offspring possess two inherited possi- 

 bilities, though they may show but one. Thus 

 in the case of a black guinea-pig, one of whose 

 parents was white, the other black, it can be 

 shown that the animal transmits both qualities 

 (black and white) which it received from its 

 respective parents, and transmits them in equal 

 measure. For, if the cross-bred black animal 

 be mated with a white one, half the offspring 

 are black and half of them white. The cross- 

 bred black animal inherited black from one 

 parent, white from the other. It showed only 

 the former, but on forming its reproductive 

 cells it transmitted black to half of these, white 

 to the other half. Hence the cross-bred black 

 individual was a duality, containing two possi- 

 bilities, black and white, but its reproductive 

 cells were again single, containing either black 

 or white, but not both. 



Now it has been shown in recent years that 

 the nuclear material in the reproductive cells 

 behaves exactly as do black and white in the 

 cross just described. This nuclear material 

 becomes doubled in amount at fertilization, 



14 



