ns are similar on both upper and under sides of
the wings. Many animals, when attacked or disturbed, "sham death" (as it
is commonly but wrongly described), falling motionless to the ground. In
the case of well-concealed animals this instinct gives them a second
chance of escape in the earth or among the leaves, &c., when they have
been once detected; animals with warning colours are, on the other hand,
enabled to assume a position in which their characters are displayed to
the full (J. Portschinsky, _Lepidopterorum Rossiae Biologia_, St
Petersburg, 1890, plate i. figs. 16, 17). In both cases a definite
attitude is assumed, which is not that of death. Other warning
characters exist in addition to colouring: thus sound is made use of by
the disturbed rattlesnake and the Indian _Echis_, &c. Large birds, when
attacked, often adopt a threatening attitude, accompanied by a
terrifying sound. The cobra warns an intruder chiefly by attitude and
the dilation of the flattened neck, the effect being heightened in some
species by the "spectacles." In such cases we often see the combination
of cryptic and sematic methods, the animal being concealed until
disturbed, when it instantly assumes an aposematic attitude. The
advantage to the animal itself is clear: a poisonous snake gains nothing
by killing an animal it cannot eat; while the poison does not cause
immediate death, and the enemy would have time to injure or destroy the
snake. In the case of small unpalatable animals with warning colours the
enemies would only first become aware of the unpleasant quality by
tasting and often destroying their prey; but the species would gain by
the experience thus conveyed, even though the individual might suffer.
An insect-eating animal does not come into the world with knowledge: it
has to be educated by experience, and warning colours enable this
education as to what to avoid to be gained by a small instead of a large
waste of life. Furthermore, great tenacity of life is usually possessed
by animals with warning colours. The tissues of aposematic insects
generally possess great elasticity and power of resistance, so that
large numbers of individuals can recover after very severe treatment.

The brilliant warning colours of many caterpillars attracted the
attention of Darwin when he was thinking over his hypothesis of sexual
selection, and he wrote to A. R. Wallace on the subject (C. Darwin,
_Life and Letters_, London, 1887, iii. 93). Wallace