Chap. VI. THEIR REVERSION IN COLOUR. 195 



meters alone. This fact is explicable through the doctrine of 

 natural selection ; for each successive modification of structure 

 in each natural species is preserved, solely because it is of 

 service ; and such modifications when largely accumulated imply 

 a great change in the habits of life, and this will almost cer- 

 tainly lead to other changes of structure throughout the whole 

 organisation. On the other hand, if the several races of the 

 pigeon have been produced by man through selection and varia- 

 tion, we can readily understand how it is that they should still 

 all resemble each other in habits and in those many characters 

 which man has not cared to modify, whilst they differ to so 

 prodigious a degree in those parts which have struck his eye or 

 pleased his fancy. 



Besides the points above enumerated, in which all the domestic 

 races resemble O. livia and each other, there is one which deserves 

 special notice. The wild rock-pigeon is of a slaty-blue colour ; 

 the wings are crossed by two black bars ; the croup varies in 

 colour, being generally white in the pigeon of Europe, and blue 

 in that of India ; the tail has a black bar close to the end, and 

 the outer webs of the outer tail-feathers are edged with white, 

 except near the tips. These combined characters are not found 

 in any wild pigeon besides 0. livia. I have looked carefully 

 through the great collection of pigeons in the British Museum, 

 and I find that a dark bar at the end of the tail is common ; 

 that the white edging to the outer tail-feathers is not rare ; 

 but that the white croup is extremely rare, and the two 

 black bars on the wings occur in no other pigeon, excepting 

 the alpine C. leuconota and 0. rupestris of Asia. Now if we 

 turn to the domestic races, it is highly remarkable, as an 

 eminent fancier, Mr. Wicking, observed to me, that, when- 

 ever a blue bird appears in any race, the wings almost 

 invariably show the double black bars. 23 The primary wing- 

 feathers may be white or black, and the whole body may be 



^ There is one exception to the rule, signifies the less as the swallow ap- 



iiamely m a sub-variety of the swal- proaches closely in structure to C. livia. 



low of German origin, which is figured In many sub-varieties the black bars 



by Neumeister, and was shown to me are replaced by bars of various colours, 



by Mr. Wickmg This bird is blue, The figures given by Neumeister are 



but has not the black wing-bars; for sufficient to show that, if the wings 



our object, however, in tracing the de- alone are blue, the black wing-bars 



scent oi the chiet races, this exception appear 



o 2 



