cies, according to their
utility. That caterpillars may be either green or brown is already
something more than could have been expected according to the old
conception of species, but that one and the same butterfly should be
now pale yellow, with black; now red with black and pure white; now
deep black with large, pure white spots; and again black with a large
ocheous-yellow spot, and many small white and yellow spots; that in
one sub-species it may be tailed like the ancestral form, and in
another tailless like its Danaid model,--all this shows a far-reaching
capacity for variation and adaptation that we could never have
expected if we did not see the facts before us. How it is possible
that the primary colour-variations should thus be intensified and
combined remains a puzzle even now; we are reminded of the modern
three-colour printing,--perhaps similar combinations of the primary
colours take place in this case; in any case the direction of these
primary variations is determined by the artist whom we know as natural
selection, for there is no other conceivable way in which the model
could affect the butterfly that is becoming more and more like it. The
same climate surrounds all four forms of female; they are subject to
the same conditions of nutrition. Moreover, _Papilio dardanus_ is by
no means the only species of butterfly which exhibits different kinds
of colour-pattern on its wings. Many species of the Asiatic genus
Elymnias have on the upper surface a very good imitation of an immune
Euploeine (Danainae), often with a steel-blue ground-colour, while the
under surface is well concealed when the butterfly is at rest,--thus
there are two kinds of protective coloration each with a different
meaning! The same thing may be observed in many non-mimetic
butterflies, for instance in all our species of Vanessa, in which the
under side shows a grey-brown or brownish-black protective coloration,
but we do not yet know with certainty what may be the biological
significance of the gaily coloured upper surface.

In general it may be said that mimetic butterflies are comparatively
rare species, but there are exceptions, for instance _Limenitis
archippus_ in North America, of which the immune model (_Danaida
plexippus_) also occurs in enormous numbers.

In another mimicry-category the imitators are often more numerous than
the models, namely in the case of the imitation of _dangerous insects_
by harmless species. Bees and