46 BREEDING 



before, because in the peas where self-fertilisation 

 always takes place, when it is not artificially prevented, 

 like always mates with like, so that there is no chance 

 of a hybrid mating with a dominant ; and because 

 in the case of the Andalusian fowl, the hybrid differed 

 from the dominant (which we called the black type 

 for convenience, and not without justification) in 

 visible characteristics. This difficulty presents itself 

 not only in the case of human eye colour, but in all 

 cases in which self-fertilisation does not occur, and 

 the hybrid is externally indistinguishable from the 

 dominant parent. The practical solution of the 

 difficulty is to rna^e the individual in question with 

 one bearing the recessive character. If all the off- 

 spring bear the dominant character, it was a pure 

 dominant ; if half bear the dominant and half the 

 recessive, it was a hybrid. Another reason why it 

 is better to test the nature of an individual bearing 

 the dominant character by mating it with a recessive, 

 than by mating it with a hybrid, is that if the 

 individual tested is a hybrid it will only produce 

 one recessive in every four in the latter case, but 

 will produce one in every two in the former. And 

 where only a small total number of offspring can be 

 raised this is obviously an advantage. 



I have discussed this at some length, because it 

 is a question which is very likely to crop up in practice 

 and because I wish to lay emphasis on a general pro- 

 perty of the hybrid, namely, that when hybrids are 

 mated with recessives they produce hybrids and reces- 

 sives in equal numbers, and when mated with domi- 



