such caterpillars are green, the upper surface, which is naturally
exposed to the light, being darker than the lower which is in shadow.
When the caterpillar is large, the green area is often broken up by pale
lines, longitudinal as on the larvae of many Owl Moths (Noctuidae) or
oblique, as on the great caterpillars of most Hawk Moths (Sphingidae).
Such an arrangement tends to make the insect less easily seen than were
it to display a continuous area of the same colour. The 'looper'
caterpillars mentioned above afford remarkable examples of 'protective'
resemblance, for many of them show a marvellous likeness to the twigs of
their food-plant, tubercles on the insect's body resembling closely the
little outgrowths of the plant's cortex. It has been shown by E.B.
Poulton (1892) that many caterpillars are, in their early stages,
directly responsive to their surroundings as regards colour. Usually
green when hatched, they remain green if kept among leaves or young
shoots of plants, while they turn red, brown, or blackish if placed
among twigs of these respective hues. This effect appears to be due to a
direct response of the subcutaneous tissue to the rays of light
reflected from the surrounding objects. The sensitiveness dies away as
the caterpillar grows older, since little or no change of hue in
response to a change of environment could be induced after the
penultimate moult.

[7] The 'hairs' of an insect are not in the least comparable to the
hairs of mammals, being in truth, modified portions of the cuticle,
secreted by special cells.

Among those families of the Lepidoptera which are usually regarded as
low in the scale of organisation, caterpillars are very generally
protected by the habit of feeding in some concealed situation. For
example, the great larvae of the Goat Moth (Cossus) and the whitish