never affected by the variation. The pursuers of the
butterfly have no time to trouble about entomological intricacies.

I must not pass over a discovery of Poulton's which is of great
theoretical importance--that mimetic butterflies may reach the same
effect by very different means. ("Journ. Linn. Soc. London (Zool.)",
Vol. XXVI. 1898, pages 598-602.) Thus the glass-like transparency of the
wing of a certain Ithomiine (Methona) and its Pierine mimic (Dismorphia
orise) depends on a diminution in the size of the scales; in the Danaine
genus Ituna it is due to the fewness of the scales, and in a third
imitator, a moth (Castnia linus var. heliconoides) the glass-like
appearance of the wing is due neither to diminution nor to absence of
scales, but to their absolute colourlessness and transparency, and to
the fact that they stand upright. In another moth mimic (Anthomyza) the
arrangement of the transparent scales is normal. Thus it is not some
unknown external influence that has brought about the transparency of
the wing in these five forms, as has sometimes been supposed. Nor is it
a hypothetical INTERNAL evolutionary tendency, for all three vary in a
different manner. The cause of this agreement can only lie in selection,
which preserves and intensifies in each species the favourable
variations that present themselves. The great faithfulness of the copy
is astonishing in these cases, for it is not THE WHOLE wing which is
transparent; certain markings are black in colour, and these contrast
sharply with the glass-like ground. It is obvious that the pursuers
of these butterflies must be very sharp-sighted, for otherwise the
agreement between the species could never have been pushed so far. The
less the enemies see and observe, the more defective must the imitation
be, and if they had been blind, no visible resemblance between the
species which required protection could ever have arisen.

A seemingly irreconcilable contradiction to the mimicry theory is
presented in the following cases, which were known to Bates, who,
however, never succeeded in bringing them into line with the principle
of mimicry.

In South America there are, as we have already said, many mimics of the
immune Ithomiinae (or as Bates called them Heliconidae). Among these
there occur not merely species which are edible, and thus require the
protection of a disguise, but others which are rejected on account of
their unpalatableness. How could the Ithomiine