seeds, as sparrows. Others for the softer
kinds of flowers, or the buds of trees, as the finches. Other birds have
acquired long beaks to penetrate the moister soils in search of insects
or roots, as woodcocks, and others broad ones to filtrate the water of
lakes and to retain aquatic insects. All which seem to have been
gradually produced during many generations by the perpetual endeavors of
the creature to supply the want of food, and to have been delivered to
their posterity with constant improvement of them for the purpose
required" (p. 238).

7. The third great want among animals is that of security, which seems
to have diversified the forms of their bodies and the color of them;
these consist in the means of escaping other animals more powerful than
themselves.[155] Hence some animals have acquired wings instead of legs,
as the smaller birds, for purposes of escape. Others, great length of
fin or of membrane, as the flying-fish and the bat. Others have acquired
hard or armed shells, as the tortoise and the Echinus marinus (p. 239).

"The colors of insects," he says, "and many smaller animals
contribute to conceal them from the dangers which prey upon them.
Caterpillars which feed on leaves are generally green; earthworms
the color of the earth which they inhabit; butterflies, which
frequent flowers, are colored like them; small birds which frequent
hedges have greenish backs like the leaves, and light-colored
bellies like the sky, and are hence less visible to the hawk, who
passes under them or over them. Those birds which are much amongst
flowers, as the goldfinch (_Fringilla carduelis_), are furnished
with vivid colors. The lark, partridge, hare, are the color of dry
vegetables or earth on which they rest. And frogs vary their color
with the mud of the streams which they frequent; and those which
live on trees are green. Fish, which are generally suspended in
water, and swallows, which are generally suspended in air, have
their backs the color of the distant ground, and their bellies of
the sky. In the colder climates many of these become white during
the existence of the snows. Hence there is apparent design in the
colors of animals, whilst those of vegetables seem consequent to
the other properties of the materials which possess them" (_The
Loves of the Plants_, p. 38, note).

In his _Zoonomia_ (Sec. xxxix., vi.) Darwin also speaks of the efficient
cause of the variou