Chap. VI. THEIR REVERSION IN COLOUR. 211 



is accounted for on the well-known principle of " throwing 

 back " or reversion. Why crossing should give so strong a 

 tendency to reversion, we do not with certainty know ; but 

 abundant evidence of this fact will be given in the following 

 chapters. It is probable that I might have bred even for 

 a century pure black Barbs, Spots, Nuns, white Fantails, 

 Trumpeters, &c, without obtaining a single blue or barred 

 bird ; yet b} 7 crossing these breeds I reared in the first and 

 second generation, during the course of only three or four 

 years, a considerable number of young birds, more or less 

 plainly coloured blue, and with most of the characteristic 

 marks. When black and white, or black and red birds, are 

 crossed, it would appear that a slight tendency exists in both 

 parents to produce blue offspring, and that this, when com- 

 bined, overpowers the separate tendency in either parent to 

 produce black, or white, or red offspring. 



If we reject the belief that all the races of the pigeon are 

 the modified descendants of C. Ucia, and suppose that they 

 are descended from several aboriginal stocks, then we must 

 choose between the three following assumptions : firstly, that 

 at least eight or nine species formerly existed which were 

 aboriginally coloured in various ways, but have since varied 

 in exactly the same manner so as to assume the colouring 

 of C. livia ; but this assumption throws not the least light on 

 the appearance of such colours and marks when the races are 

 crossed. Or secondly, we may assume that the aboriginal 

 species were all coloured blue, and had the wing-bars and 

 other characteristic marks of C. livia, — a supposition which is 

 highly improbable, as besides this one species no existing 

 member of the Columbidae presents these combined cha- 

 racters; and it would not be possible to find any other 

 instance of several species identical in plumage, yet as 

 different in important points of structure as are Pouters, 

 Fantails, Carriers, Tumblers, &c. Or lastly, we may assume 

 that all the races, whether descended from C. livia or from 

 several aboriginal species, although they have been bred 

 with so much care and are so highly valued by fanciers, have 

 all been crossed within a dozen or score of generations with 

 C. livia, and have thus acquired their tendency to produce 



