REPRODUCTION 89 



same would hold true of the females ; each one 

 would give rise to equal numbers of black 

 eggs and of white eggs. 



If, now, we imagine these two kinds of eggs 

 to be fertilized by the two kinds of sperm and 

 that the combinations be purely fortuitous, we 

 would expect four classes of fertilized eggs of 

 equal frequency ; once in four a white egg 

 would be fertilized by a white sperm, once in 

 four a black egg by a black sperm ; once in 

 four a black egg by a white sperm ; and once 

 in four a white egg by a black sperm. The 

 first class would yield the twenty-five per cent 

 of pure white individuals, the second the same 

 per cent of pure black individuals, and the 

 third and fourth the fifty per cent of black 

 individuals which are, however, capable of 

 producing white as well as black offspring. 

 Thus the assumption of the purity of the 

 germ, the segregation of characteristics, makes 

 clear these very remarkable proportions as 

 seen in the actual experiments in heredity. 



The conception of the hereditary proc- 

 ess which has grown out of this idea and 



o 



the way in which this process is supposed 

 to have impressed itself upon the face of 

 nature is well seen in the mutation theory 



