166 DOMESTIC PIGJJONS : Chap. Y. 



as Tiirbits and sliort-faced Tumblers. The remainina: do 

 mestit forms miglit have been included jin the same genua 

 with the wild rock-pigeon. 



Individual Varidbilitij ; variations of a remarkahle 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- 

 A'idual 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 oiir 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 conspiciTons part. At the present day any visible 

 deviation of character in a well-established breed is rejected 

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

 period, before well-marked breeds had been formed, such 

 deviations would have been rejected ; on the contrary, they 

 would have been eagerly preserved as presenting a novelty, 

 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 in the several breeds, aud have hardly ever found them quite 

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

 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 tirst mention, as some readers may not be aware of the 

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

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

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

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

 in number ; b\it this does not apply to the several sijecies and genera 

 of the Columbid£E, which never (^as far as I can hear) have less than 

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



