DOMESTIC MG£ONS. 21 



Specified marks, the mongrel offspring are very apt suddenly 

 to acquire these characters. To give one instance out of 

 several which I have observed : I crossed some white fan- 

 tails, which breed very true, with some black barbs — and it 

 so happens that blue varieties of barbs are so rare that I 

 never heard of an instance in England; and the mongrels 

 were black, brown, and mottled. I also crossed a barb with 

 a spot, which is a white bird with a red tail and red spot on 

 the forehead, and which notoriously breeds very true ; the 

 mongrels were dusky and mottled. I then crossed one of 

 the mongrel barb-fantails with a mongrel barb-spot, and they 

 produced a bird of as beautiful a blue color, with the white 

 loins, double black wing-bar, and barred and white-edged 

 tail-feathers, as any wild rock-pigeon ! We can understand 

 these facts, on the well-known principle of reversion to 

 ancestral characters, if all the domestic breeds are descended 

 from the rock-pigeon. But, if we deny this, we must make 

 one of the two following highly improbable suppositions. 

 Either, first, that all the several imagined aboriginal stocks 

 were colored and marked like the rock-pigeon, although no 

 other existing species is thus colored and marked, so that in 

 each separate breed there might be a tendency to revert to 

 the very same colors and markings. Or, secondly, that each 

 breed, even the purest, has within a dozen, or at most within 

 a score, of generations, been crossed by the rock-pigeon : I 

 say within a dozen or twenty generations, for no instance is 

 known of crossed descendants reverting to an ancestor of 

 foreign blood, removed by a greater number of generations. 

 In a breed which has been crossed only once the tendency to 

 revert to any character derived from such a cross will natur^ 

 ally become less and less, as in each succeeding generation 

 there will be less of the foreign blood; but when there hai 

 been no cross, and there is a tendency in the breed to revert 

 to a character which was lost during some former generation, 

 this tendency, for all that we can see to the contrary, may 

 be transmitted undiminished for an indefinite number of 

 generations. These two distinct cases of reversion are 

 often confounded together by those who have written on 

 inheritance. 



Lastly, the hybrids or mongrels from between all the 

 breeds of the pigeon are perfectly fertile, as I can state 

 from my own observations, purposely made, on the most 

 distinct breeds. Now, hardly any cases have been ascer- 

 tained with certainty of hybrids from two quite distinct 



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