looking down into the water; while
the white under-surface makes them less visible from below. The animals
of the desert are sand-coloured; those of the Arctic regions are white
like snow, especially in winter; and pelagic animals are blue.

Let us take certain special cases. The Lion, like other desert animals,
is sand-coloured; the Tiger which lives in the Jungle has vertical
stripes, making him difficult to see among the upright grass; Leopards
and the tree-cats are spotted, like rays of light seen through leaves.

An interesting case is that of the animals living in the Sargasso or
gulf-weed of the Atlantic. These creatures--Fish, Crustacea, and
Mollusks alike--are characterised by a peculiar colouring, not
continuously olive like the Seaweed itself, but blotched with rounded
more or less irregular patches of bright, opaque white, so as closely to
resemble fronds covered with patches of Flustra or Barnacles.

Take the case of caterpillars, which are especially defenceless, and
which as a rule feed on leaves. The smallest and youngest are green,
like the leaves on which they live. When they become larger, they are
characterised by longitudinal lines, which break up the surface and thus
render them less conspicuous. On older and larger ones the lines are
diagonal, like the nerves of leaves. Conspicuous caterpillars are
generally either nauseous in taste, or protected by hairs.

[Illustration: Fig. 1.--_Choerocampa porcellus._]

I say "generally," because there are some interesting exceptions. The
large caterpillars of some of the Elephant Hawkmoths are very
conspicuous, and rendered all the more so by the presence of a pair of
large eyelike spots. Every one who sees one of these caterpillars is
struck by its likeness to a snake, and the so-called "eyes" do much to
increase the deception. Moreover, the ring on which they are placed is
swollen, and the insect, when in danger, has the habit of retracting its
head and front segments, which gives it an additional resemblance to
some small reptile. That small birds are, as a matter of fact, afraid of
these caterpillars (which, however, I need not say, are in reality
altogether harmless) Weismann has proved by actual experiment. He put
one of these caterpillars in a tray, in which he was accustomed to place
seed for birds. Soon a little flock of sparrows and other small birds
assembled to feed as usual. One of them lit on the edge of this tray,
and was just going to hop