ed by day, it is by no means always the case that they are
brown; some of them still retaining the green color. We may then
conclude that the habit of concealing themselves by day came first,
and that the brown color is a later adaptation. It is, moreover,
interesting to note that while the caterpillars which live on low
plants often go down to the ground and turn brown, those which feed on
large trees or plants remain on the under side of the leaves, and
retain their green color.

Thus, in the Eyed Hawk-moth, which feeds on the willow and sallow; the
Poplar Hawk-moth, which feeds on the poplar; and the Lime Hawk-moth,
which frequents the lime, the caterpillars all remain green; while in
those which frequent low plants, such as the Convolvulus Hawk-moth,
which frequents the convolvulus; the Oleander Hawk-moth, which feeds
in this country on the periwinkle; and other species, most of the
caterpillars turn brown. There are, indeed, some caterpillars which
are brown, and still do not go down to the ground--as, for instance,
those of the Geometridae generally. These caterpillars, however, as
already mentioned, place themselves in peculiar attitudes, which,
combined with their brown color, make them look almost exactly like
bits of stick or dead twigs.

The last of the five points to which I called your attention was the
eye-spots. In some cases, spots may serve for concealment, by
resembling the marks on dead leaves. In one species, which feeds on
the hippophae, or sea buckthorn, a gray-green plant, the caterpillar
also is a similar gray-green, and has, when full grown, a single red
spot on each side--which, as Weissmann suggests, at first sight much
resembles in color and size one of the berries of the hippophae. This
might, at first, be supposed to constitute a danger, and therefore to
be a disadvantage; but the seeds, though present, are not ripe, and
consequently are not touched by birds. Again, in another caterpillar,
there is an eye-spot on each segment, which mimics the flower of the
plant on which it feeds. White spots, in some cases, also resemble the
spots of light which penetrate foliage. In other instances, however,
and at any rate in our Elephant Hawk-moth, the eye-spots certainly
render the insect more conspicuous.

Now in some cases, this is an advantage, rather than a drawback.
Suppose that from the nature of its food, from its being covered with
hair, or from any other cause, a small green caterpillar we