theless
some slight amount of change may, I think, be attributed to the direct
action of the conditions of life--as, in some cases, increased size from
amount of food, colour from particular kinds of food and from light, and
perhaps the thickness of fur from climate.

Habit also has a decided influence, as in the period of flowering with
plants when transported from one climate to another. In animals it has
a more marked effect; for instance, I find in the domestic duck that
the bones of the wing weigh less and the bones of the leg more,
in proportion to the whole skeleton, than do the same bones in the
wild-duck; and I presume that this change may be safely attributed to
the domestic duck flying much less, and walking more, than its wild
parent. The great and inherited development of the udders in cows and
goats in countries where they are habitually milked, in comparison with
the state of these organs in other countries, is another instance of the
effect of use. Not a single domestic animal can be named which has not
in some country drooping ears; and the view suggested by some authors,
that the drooping is due to the disuse of the muscles of the ear, from
the animals not being much alarmed by danger, seems probable.

There are many laws regulating variation, some few of which can be dimly
seen, and will be hereafter briefly mentioned. I will here only allude
to what may be called correlation of growth. Any change in the embryo
or larva will almost certainly entail changes in the mature animal. In
monstrosities, the correlations between quite distinct parts are very
curious; and many instances are given in Isidore Geoffroy St. Hilaire's
great work on this subject. Breeders believe that long limbs are almost
always accompanied by an elongated head. Some instances of correlation
are quite whimsical; thus cats with blue eyes are invariably deaf;
colour and constitutional peculiarities go together, of which many
remarkable cases could be given amongst animals and plants. From the
facts collected by Heusinger, it appears that white sheep and pigs are
differently affected from coloured individuals by certain vegetable
poisons. Hairless dogs have imperfect teeth; long-haired and
coarse-haired animals are apt to have, as is asserted, long or many
horns; pigeons with feathered feet have skin between their outer toes;
pigeons with short beaks have small feet, and those with long beaks
large feet. Hence, if man goes on selectin