a 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 vertebra, 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 
