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 selecting,
and thus augmenting, any peculiarity, he will almost certainly
unconsciously modify other parts of the structure, owing to the
mysterious laws of the correlation of growth.

The result of the various, quite unknown, or dimly seen laws of
variation is infinitely complex and diversified. It is well worth