416 PHENOMENA OF ORGANIC NATURE xi 



while, on the other hand, the little Tumbler is so 

 called because of its extraordinary faculty of turn- 

 ing head over heels in the air, instead of pursuing 

 a direct course. And, lastly, the dispositions and 

 voices of the birds may vary. Thus the case of 

 the pigeons shows you that there is hardly a 

 single particular whether of instinct, or habit, 

 or bony structure, or of plumage of either the 

 internal economy or the external shape, in which 

 some variation or change may not take place, 

 which, by selective breeding, may become perpetu- 

 ated, and form the foundation of, and give rise to, 

 a new race. 



If you carry in your mind's eye these four 

 varieties of pigeons, you will bear with you as 

 good a notion as you can have, perhaps, of the 

 enormous extent to which a deviation from a 

 primitive type may be carried by means of this 

 process of selective breeding. 



The birds which fly long distances, and come home "homing " 

 birds and are consequently used as earners, are not "carriers" 

 in the fancy sense. 



