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 carriers, are not ‘‘ carriers” 
in the fancy sense. 
