VARIATION UNDER DOMESTICATION 49 



highly remarkt-blo m£>aner. The caudal and sacral ver e- 

 brae vary ia number; as does the number of the ribs, 

 together with their relative breadth and the presence of 

 processes. The size and shape of the apertures in the 

 sternum are highly variable; so is the degree of diver- 

 gence and relative size of the two arms of the furcula. 

 The proportional width ol tne gape of mouth, the propor- 

 tional length of the eyelids, of the orifice of the nostrils, 

 of the tongue (not always in strict correlation with the 

 length of beak), the size of the crop and of the upper 

 part of the oesophagus; the development and abortion of 

 the oil-gland; the number of the primary wing and caudal 

 feathers; the relative length of the wing and tail to each 

 other and to the body; the relative length of the leg and 

 foot; the number of scutellsB on the toes, the develop- 

 ment of skin between the toes, are all points of structure 

 which are variable. The period at which the perfect 

 plumage is acquired varies, as does the state of the down 

 with which the nestling birds are clothed when hatched. 

 The shape and size of the eggs vary. The manner of 

 flight, and in some breeds the voice and disposition, differ 

 remarkably. Lastly, in certain breeds, the males and 

 females have come to differ in a slight degree from each 

 other. 



Altogether at least a score of pigeons might be chosen, 

 which, if shown to an ornithologist, and he were told that 

 they were wild birds, would certainly be ranked by him 

 as well-defined species. Moreover, I do not believe that 

 any ornithologist would in this case place the English 

 carrier, the short-faced tumbler, the runt, the barb, pouter, 

 and fantail in the same genus; more especially as in 



each of these breeds several truly-inherited sub-breeds, 



—Science — 3 



