n THE ORIGIN OF SPECIES 43 



the genera and species of birds differ from one 

 another. 



And it is most remarkable and instructive to 

 observe, that none of these races can be shown to 

 have been originated by the action of changes in 

 what are commonly called external circumstances, 

 upon the wild rock-pigeon. On the contrary, 

 from time immemorial pigeon -fanciers have had 

 essentially similar methods of treating their pets, 

 which have been housed, fed, protected and cared 

 for in much the same way in all pigeonries. In 

 fact, there is no case better adapted than that of 

 the pigeons to refute the doctrine which one sees 

 put forth on high authority, that "no other 

 characters than those founded on the development 

 of bone for the attachment of muscles" are 

 capable of variation. In precise contradiction of 

 this hasty assertion, Mr. Darwin's researches 

 prove that the skeleton of the wings in domestic 

 pigeons has hardly varied at all from that of the 

 wild type ; while, on the other hand, it is in exactly 

 those respects, such as the relative length of the 

 beak and skull, the number of the vertebrae, and 

 the number of the tail-feathers, in which muscular 

 exertion can have no important influence, that 

 the utmost amount of variation has taken place. 



We have said that the following out of the 

 properties exhibited by physiological species would 

 lead us into difficulties, and at this point they begin 



