Chap. I.] DOMESTIC PIGEONS. 29 



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 colour, with the white loins, double 

 black wino-bar, and barred and white-ed^ed tail- 

 feathers, as any wild rock-pigeon ! We can under- 

 stand these facts, on the well-known principle of 

 reversion to ancestral characters, if all the domestio 

 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 coloured 

 and marked like the rock-pigeon, although no other 

 existing species is thus coloured and marked, so that 

 in each separate breed there might be a tendency to 

 revert to the very same colours 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 naturally become less and less, as in each suc- 

 ceeding generation there will be less of the foreign 

 blood ; but when there has been no cross, and there 



