[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.
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