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 perpetuated, and form the foundation of,
and give rise to, a new race.

[footnote: The "Carrier," I learn from Mr. Tegetmeier, does
not 'carry'; a high-bred bird of this breed being but a
poor flier. The birds which fly long distances, and come
home,--"homing" birds,--and are consequently used as
carriers, are not "carriers" in the fancy sense.]

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.