f offence, the creatures in
question present a fictitiously dangerous aspect. As the
Devil's-coach-horse turns up his stingless tail when threatened by an
enemy, so in numberless ways do many harmless animals of all classes
pretend to be formidable. But the point now is that these instincts of
self-defence are often helped out by structural modifications,
expressly and exclusively adapted to this end. For example, what a
remarkable series of protective adjustments occurs in the life-history
of the Puss Moth--culminating with so comical an instance of the
particular device now under consideration as the following. I quote the
facts from Mr. E. B. Poulton's admirable book on _The Colours of
Animals_ (pp. 269-271).

[Illustration: FIG. 111.--The larva of Puss Moth (_C. vinula_)
when undisturbed; full-fed; natural size.]

The larva of the Puss Moth (Cerura vinula) is very common upon
poplar and willow. The circular dome-like eggs are laid, either
singly or in little groups of two or three, upon the upper side of
the leaf, and being of a reddish colour strongly suggest the
appearance of little galls, or the results of some other injury to
the leaf. The youngest larvae are black, and also rest upon the
upper surface of the leaf, resembling the dark patches which are
commonly seen in this position. As the larva grows, the apparent
black patch would cover too large a space, and would lead to
detection if it still occupied the whole surface of the body. The
latter gains a green ground-colour which harmonises with the leaf,
while the dark marking is chiefly confined to the back. As growth
proceeds the relative amount of green increases, and the dark mark
is thus prevented from attaining a size which would render it too
conspicuous. In the last stage of growth the green larva becomes
very large, and usually rests on the twigs of its food-plant (Fig.
111). The dark colour is still present on the back but is softened
to a purplish tint, which tends to be replaced by a combination of
white and green in many of the largest larvae. Such a larva is well
concealed by General Protective Resemblance, and one may search a
long time before finding it, although assured of its presence from
the stripped branches of the food-plant and the faeces on the ground
beneath.

[Illustration: FIG. 112.--The larva of Puss M