SCOPE OF GENETICS 19 



the factors segregating- from each other in 

 cell-division, or even if by microscopic ex- 

 amination we could recognize this multitu- 

 dinous diversity of composition that must 

 certainly exist among the germ-cells of all 

 ordinary individuals, the work of genetics 

 would be much simpler than it is. 



But so far no such direct method of 

 observation has been discovered. In default 

 we are obliged to examine the constitution 

 of the germ-cells by experimental breeding, 

 so contrived that each mating shall test the 

 composition of an individual in one or more 

 chosen respects, and, so to speak, sample its 

 germ -cells by counting the number of each 

 kind of offspring which it can produce. But 

 cumbersome as this method must necessarily 

 be, it enables us to put questions to Nature 

 which never have been put before. She, it 

 has been said, is an unwilling witness. Our 

 questions must be shaped in such a way that 



2—2 



