10 THE METHODS AND 



taken. But in either chest one or more of 

 the bottles may be empty; then nothing 

 goes in to represent that ingredient from 

 that chest, and if corresponding bottles are 

 empty in both chests, then the individual 

 made on fertilisation by mixing the two 

 collections of drops together does not con- 

 tain the missing ingredient at all. It follows 

 therefore that an individual may thus be 

 "pure-bred," namely alike on both sides of 

 his composition as regards each ingredient 

 in one of two ways, either by having received 

 the ingredient from the male chest and from 

 the female, or in having received it from 

 neither. Conversely in respect of any in- 

 gredient he may be "cross-bred," receiving 

 the presence of it from one gamete and the 

 absence of it from the other. 



The second conception with which we 

 have now to become thoroughly familiar is 



