of the variations produced by the species, 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 ochreous-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 wide 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.