246 THE BREEDING OF ANIMALS 



own breed. This is particularly the case if the two ani- 

 mals mated are the result of long-continued in-breeding 

 and are themselves also near of kin. 



In the instance of in-breeding pigs by J. Wright already 

 cited, the seventh generation resulting from close in- 

 breeding consisted of one sow. This sow was infertile 

 when bred to her sire, but bred readily with an unrelated 

 boar. Darwin cites numerous instances of increased 

 fertility due to crossing. Mr. Eyton, 1 a breeder of Grey 

 Dorkings, found it necessary to increase the prolificacy 

 and increase the size of his in-bred stock by cross- 

 ing. Bates, 2 the great breeder of Shorthorn cattle, bred 

 closely in-and-in for thirteen years, but then found 

 it necessary to " infuse fresh blood, not to improve 

 the form of the animals but on account of lessened 

 fecundity." 



Bloodhounds 3 closely in-bred lost their fertility, which 

 was restored by a single cross. 



Many plants are infertile unless cross-fertilized with 

 the pollen of another variety. 



230. Cross-breeding to increase size and restore 

 constitution. The tendency of in-breeding to decrease 

 the size is promptly corrected by cross-breeding. " The 

 good effects of a cross are at once shown by the greater 

 size of the offspring." 



It is the common experience of breeders that highly 

 improved strains of cattle, hogs or sheep sometimes show 

 a refinement or delicacy of constitution which in a measure 

 interferes with the economic value. In such cases a sud- 

 den out-cross to another equally valuable strain may 



1 Darwin, "Animals and Plants under Domestication," vol. 

 II, p. 105. 



2 Ibid. 



3 Loc. cit. 



