ultimate particles are grouped, the metallic red of the Phanaeus, as
well as the white, the dull red and the black of the Sacred Beetle. It
becomes black on the dorsal surface of the Stercoraceous Geotrupes and
the Mimic Geotrupes; and, with a quick change, it turns into amethyst
under the belly of the first and into copper pyrites under the belly
of the second. It covers the back of _Cetonia floricola_ with golden
bronze and the under surface with metallic purple. According to the
insect, according to the part of the body, it remains a dingy compound
or sparkles with reflections even more vivid and varied than those
possessed by the metals.

Light seems irrelevant to the development of these splendours; it
neither accelerates nor retards them. Since direct exposure to the
sun, owing to the excess of heat, is fatal to the delicate process of
the nymphosis, I shaded the solar rays with a screen of water
contained between slips of glass; and to the bright light thus
moderated in temperature I daily, throughout the period of chromatic
evolution, subjected a number of Sacred Beetles, Geotrupes and
Cetoniae. As standards of comparison I had witnesses of whom I kept
some in diffused light and others in complete darkness. My experiments
had no appreciable result. The development of the colours took place
in the sunlight and in the dark alike, neither more rapidly nor more
slowly and without difference in the tints.

This negative result was easy to foresee. The Buprestis emerging from
the depths of the trunk in which he has spent his larval life; the
Geotrupes and the Phanaeus leaving their natal burrows possess their
final adornments, which will not become richer in the rays of the sun,
at the time when they make their appearance in the open air. The
insect does not claim the assistance of the light for its colour
chemistry, not even the Cicada,[9] who bursts her larval scabbard and
changes from pale green to brown as easily in the darkness of my
apparatus as in the sunlight, in the usual manner.

[Footnote 9: Cf. _The Life of the Grasshopper_: chaps. i. to
v.--_Translator's Note_.]

The chromatics of the insect, having as its basis the urinary waste
products, might well be found in various animals of a higher order. We
know of at least one example. The pigment of a small American lizard
is converted into uric acid under the prolonged action of boiling
hydrochloric acid.[10] This cannot be an isolated instance; and there