14 THE METHODS AND 



respect of which he is pure-bred. Expecta- 

 tion would naturally suggest that all the 

 germ-cells formed from him would be alike 

 in respect of those ingredients, and obser- 

 vation shows, except in the rare cases of 

 originating variations, the causation of which 

 is still obscure, that this expectation is 

 correct. 



Hitherto though without experimental 

 evidence no one could have been certain 

 that the facts were as I have described them, 

 yet there is nothing altogether contrary to 

 common expectation. But when we proceed 

 to ask how the germ-cells will be constituted 

 in the case of an individual who is cross-bred 

 in some respect, containing that is to say, an 

 ingredient from the one side of his parentage 

 and not from the other, the answer is entirely 

 contrary to all the preconceptions which either 

 science or common sense had formed about 



