350 



LAWS OF VARIATION 



Chap. XXVI, 



all the forms descended from the same remote progenitor having a ten- 

 dency to vary in the same manner. Thus also wo can perhaps understand 

 the fact of some Laugher-pigeons cooing almost like turtle-doves, and 

 of several races having peculiarities in their flight, for certain natural species 

 (viz. O. torquatrix and pahtmbus) display singular vagaries in this respect 

 In other cases a race, instead of imitating in character a distinct species 

 resembles some other race ; thus certain runts tremble and slightly elevate 

 their tails, like fantails ; and turbits inflate the upper part of their oeso- 

 phagus, like pouter-pigeons. 



It is a common circumstance to find certain coloured marks persistently 

 characterising all the species of a genus, but differing much in tint ; and 

 the same thing occurs with the varieties of the pigeon : thus, instead of the 

 general plumage being blue with the wing-bars black, there are snow- 

 white varieties with red bars, and black varieties with white bars ; in other 

 varieties the wing-bars, as we have seen, are elegantly zoned with different 

 tints. The Spot pigeon is characterised by the whole plumage being white 

 excepting the tail and a spot on the forehead ; but these parts may be red' 

 yellow, or black. In the rock-pigeon and in many varieties the tail is 

 blue, with the outer edges of the outer feathers white ; but in one sub- 

 variety of the monk-pigeon we have a reversed variation, for the tail is 

 white, except the outer edges of the outer feathers, which are black. 30 



With some species of birds, for instance with gulls, certain coloured parts 

 appear as if almost washed out, and I have observed exactly the same 

 appearance in the terminal dark tail-bar in certain pigeons, and in the 

 whole plumage of certain varieties of the duck. Analogous facts in the 

 vegetable kingdom could be given. 



Many sub-varieties of the pigeon have reversed and somewhat lengthened 

 feathers on the back part of their heads, and this is certainly not due to 

 reversion to the parent-species, which shows no trace of such structure ; 

 but when we remember that sub-varieties of the fowl, turkey, canary- 

 bird, duck, and goose, all have topknots or reversed feathers 'on their 

 heads ; and when we remember that scarcely a single large natural group 

 of birds can be named, in which some members have not a tuft of feathers 

 on their heads, we may suspect that reversion to some extremely remote 

 form has come into action. 



Several breeds of the fowl have either spangled or pencilled feathers • 

 and these cannot be derived from the parent-species, the Gallus bankiva • 

 though of course it is possible that an early progenitor of this 

 may have been spangled, and a still earlier or a later progenitor ^j 

 have been pencilled. But as many gallinaceous birds are spangled or 

 pencilled, it is a more probable view that the several domestic breeds 

 of the fowl have acquired this kind of plumage from all the members of 

 the family inheriting a tendency to vary in a like manner. The same 

 principle may account for the ewes in certain breeds of sheep being- 

 hornless, like the females of some other hollow-horned ruminants ; it may 

 account for certain domestic cats having slightly-tufted ears, like those of 

 the lynx ; and for the skulls of domestic rabbits often differing from each 



30 Bechstein, • Natnrgeschichte Deutschlands,' Band iv., 170", s. 31. 



species 

 may 



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