Chap. XIII. 



REVERSION. 



35 



When two distinct races are crossed, it is notorious that the 

 tendency in the offspring to revert to one or both parent-forms 

 is strong, and endures for many generations. I have myself 

 seen the clearest evidence of this in crossed pigeons and with 

 various plants. Mr. Sidney 16 states that, in a litter of Essex 

 pigs, two young ones appeared which were the image of the 

 Berkshire boar that had been used twenty-eight years before in 

 giving size and constitution to the breed. I observed in the 

 farmyard at Betley Hall some fowls showing a strong likeness 

 to the Malay breed, and was told by Mr. Toilet that he had 

 forty years before crossed his birds with Malavs ; and that, 

 though he had at first attempted to get rid of this'stiain, he had 

 subsequently given up the attempt in despair, as the Malay 

 character would reappear. 



This strong tendency in crossed breeds to revert has given 

 rise to endless discussions in how many generations after a 

 single cross, either with a distinct breed or merely with an 

 inferior animal, the breed may be considered as pure, and free 

 from all danger of reversion. No one supposes that less than 

 three generations suffices, and most breeders think that six 

 sever, or eight are necessary, and some go to still greater 

 lengths.- But neither in the case of a breed which has been 

 contaminated by a single cross, nor when, in the attempt to form 

 an intermediate breed, half-bred animals have been matched 

 together during many generations, can any rule be laid down how 

 soon the tendency to reversion will be obliterated. It depends 

 on he difference m the strength or prepotency of transmission 

 1„ *r P« ;^, on their actual amount of difference, 

 and on the nature of the conditions of life to which the crossed 



tfr: a g r r posed : But we must be <— ** *> — 



ho e XZ fTT 011 * t0 CharacterS £ ained from a ™> ™th 

 lZXZ7^ the ^ ClaSS ' ln Which cl — s originally 

 aTelr f £ f T**** ^ ^ ^ S ° me Wer P e ^ d > *> 

 =; o"atr ^ ^ ™" aft - - ^-indefinite 



186o'; h 27. edit - 0f ' Y ° UaUontlleP ^ 



17 Dr. P. Lucas, 'Hered. Nat./ torn 

 "•PP. 314, 892: seeag00dpr ' acticai 



article on the subject in ' Gard. Chro- 

 nicle,' 1856, p. 620. I could add a vast 

 number of references, but they would 

 be superfluous. 



D 2 



