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 wing-bar, and barred and white-edged 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 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 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, ok at most within a score, of generations, been 

 crossed by \the rock-pigeon: I say within a dozen or 

 twenty generjations, 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 natu/rally become less and less, as in each suc- 

 ceeding ^jeneration there will be less of the foreign 

 blood; bi'it when there has been no cross, and there 



