Illustrations of Demonstrated Mimicry.
Butterflies of other families are found as mimics of the Danaidæ and Heliconiidæ, which have been shown to be generally uneatable, and avoided by Birds, Dragonflies, Lizards, and other enemies. The fact that the writer found a Danais chrysippus being devoured by an orthopterous insect (Hemisaga prædatoria)[1] is only another illustration of the much used motto—the exception proves the rule. The glands near the anus of some Heliconiidæ have also been proved to emit a pungent odour. These facts have been recorded by Bates, Belt, Trimen, Wallace, and others. But Mr. Frank Finn, who has made some careful experiments to test the "Theory of Warning Colours and Mimicry," certainly found that his birds in captivity not only ate, but sometimes seemed to prefer, specimens of Danais and Euplœa. Nevertheless, when he experimented with birds at liberty, he had not the slightest doubt "as to the unpalatability of Danais, and the other 'warningly-coloured' forms. Birds would often look at them, and soon left them when picked up." But when he further experimented with the common garden Lizard of India (Calotes versicolor), he came to the conclusion that "the behaviour of these reptiles certainly does not appear to afford support to the belief that the butterflies at any rate, usually considered nauseous, are distasteful to them."[2]
Miss Newbigin is also a sceptic on this point, based on her physiological study of animal colouration. She remarks:—"Instead therefore of supposing that the Heliconiidæ have, in Mr. Wallace's words, 'acquired lazy habits' and a slow flight because they are uneatable, and the Pieridæ because they resemble the Heliconiidæ, may we not rather suppose that the slow flight and 'warning' colours in both cases are due to the same cause, the relatively low organisation which renders pigmentation by waste products possible, which makes brilliant optical colours impossible?"[3] As appertaining to this subject, Mr. Hopkins has demonstrated the presence of uric acid in the wing-pigments of the Pieridæ, and observes:—"The described uric acid derivatives, though
