ges of colour when exposed to differently coloured surroundings.
This subject has been carefully investigated by Mr. E.B. Poulton, who
has communicated the results of his experiments to the Royal
Society.[65] It had been noticed that some species of larvae which fed
on several different plants had colours more or less corresponding to
the particular plant the individual fed on. Numerous cases are given in
Professor Meldola's article on "Variable Protective Colouring" (_Proc.
Zool. Soc._, 1873, p. 153), and while the general green coloration was
attributed to the presence of chlorophyll beneath the skin, the
particular change in correspondence to each food-plant was attributed to
a special function which had been developed by natural selection. Later
on, in a note to his translation of Weissmann's _Theory of Descent_,
Professor Meldola seemed disposed to think that the variations of colour
of some of the species might be phytophagic--that is, due to the direct
action of the differently coloured leaves on which the insect fed. Mr.
Poulton's experiments have thrown much light on this question, since he
has conclusively proved that, in the case of the sphinx caterpillar of
Smerinthus ocellatus, the change of colour is not due to the food but to
the coloured light reflected from the leaves.

This was shown by feeding two sets of larvae on the same plant but
exposed to differently coloured surroundings, obtained by sewing the
leaves together, so that in one case only the dark upper surface, in the
other the whitish under surface was exposed to view. The result in each
case was a corresponding change of colour in the larvae, confirming the
experiments on different individuals of the same batch of larvae which
had been supplied with different food-plants or exposed to a different
coloured light.

An even more interesting series of experiments was made on the colours
of pupae, which in many cases were known to be affected by the material
on which they underwent their transformations. The late Mr. T.W. Wood
proved, in 1867, that the pupae of the common cabbage butterflies
(Pieris brassicae and P. rapae) were either light, or dark, or green,
according to the coloured boxes they were kept in, or the colours of the
fences, walls, etc., against which they were suspended. Mrs. Barber in
South Africa found that the pupae of Papilio Nireus underwent a similar
change, being deep green when attached to orange leaves of the same
tint, pal