166 DOMESTIC PIGEONS : Chap. V 



as Turbits and short-faced Tumblers. The remaining do- 

 mestic forms might have been included, in the same genua 

 with the wild rock-pigeon. 



Individual Variability ; variations of a remarkable nature. 



The differences which we have as yet considered are charac- 

 teristic of distinct breeds; but there are other differences, 

 either confined to individual birds, or often observed in 

 certain breeds but not characteristic of them. These indi- 

 vidual differences are of importance, as they might in most 

 cases be secured and accumulated by man's power of selection 

 and thus an existing breed might be greatly modified or a 

 new one formed. Fanciers notice and select only those slight 

 differences which are externally visible; but the whole 

 organisation is so tied together by correlation of growth, 

 that a change in one part is frequently accompanied by other 

 changes. For our purpose, modifications of all kinds are 

 equally important, and if affecting a part which does not 

 commonly vary, are of more importance than a modification 

 in some conspicuous part. At the present day any visible 

 deviation of character in a well-established breed is rejected 

 us a blemish; but it by no means follows that at an early 

 period, before well marked breeds hud been formed, such 

 deviations would have been rejected; on the contrary, they 

 would have been eagerly preserved as presenting a noveHy, 

 and would then have been slowly augmented, as we shall here- 

 after more clearly see, by the process of unconscious selection. 



I have made numerous measurements of the various parts of the 

 body m the several breeds, and have hardly ever found them quite 

 the same in birds of the same breed, — the differences being greater 

 than we commonly meet with in wild species within the same 

 district. To begin with the primary feathers of the wing and tail ; 

 but I must first mention, as some readers may not be aware of the 

 tact, that the number of the primary wing and tail-feathers in wild 

 birds is generally constant, and characterises, not only whole genera, 

 but even whole families. When the tail-feathers are unusually 

 numerous, as for instance in the swan, they are apt to be variable 

 in number ; but this does not apply to the several species and genera 

 of the Columbkhe, which never (as far as I can hear) have less than 

 twelve or more than sixteen tail-feathers; and these numbers cha- 



