oth in its terrifying
attitude after being disturbed; full-fed; natural size.]

As soon as a large larva is discovered and disturbed it withdraws
its head into the first body-ring, inflating the margin, which is
of a bright red colour. There are two intensely black spots on this
margin in the appropriate position for eyes, and the whole
appearance is that of a large flat face extending to the outer edge
of the red margin (see Fig. 112). The effect is an intensely
exaggerated caricature of a vertebrate face, which is probably
alarming to the vertebrate enemies of the caterpillar. The
terrifying effect is therefore mimetic. The movements entirely
depend on tactile impressions: when touched ever so lightly a
healthy larva immediately assumes the terrifying attitude, and
turns so as to present its full face towards the enemy; if touched
on the other side or on the back it instantly turns its face in the
appropriate direction. The effect is also greatly strengthened by
two pink whips which are swiftly protruded from the prongs of the
fork in which the body terminates. The prongs represent the last
pair of larval legs which have been greatly modified from their
ordinary shape and use. The end of the body is at the same time
curved forward over the back (generally much further than in Fig.
112), so that the pink filaments are brandished above the head.

_Mimicry._

Lastly, these facts as to imitative and conspicuous colouring lead on to
the yet more remarkable facts of what is called mimicry. By mimicry is
meant the imitation in form and colour of one species by another, in
order that the imitating species may be mistaken for the imitated, and
thus participate in some advantage which the latter enjoys. For
instance, if, as in the case of the conspicuously-coloured caterpillars,
it is of advantage to an ill-savoured species that it should hold out a
warning to enemies, clearly it may be of no less advantage to a
well-savoured species that it should borrow this flag, and thus be
mistaken for its ill-savoured neighbour. Now, the extent to which this
device of mimicry is carried is highly remarkable, not only in respect
of the number of its cases, but also in respect of the astonishing
accuracy which in most of these cases is exhibited by the imitation.
There need be little or virtually no zoological affinity between the
i