[[p. lxxx]] Mr. A. R. Wallace requested the assistance of Members in making observations to enable him to clear up a difficult point. Mr. Darwin had arrived at the conclusion that, as a rule in the animal kingdom, brilliant colouring was due to sexual selection: being struck, however, by the apparent exception to this rule presented by the bright hues of many larvæ, principally of Lepidoptera, which, being sexless, could not owe their gaudy attire to sexual selection, Mr. Darwin had inquired whether Mr. Wallace could suggest any explanation of this seeming contradiction of the rule. A theoretical explanation occurred to him, and it was for the purpose of ascertaining whether this theory was well or ill founded that he asked the aid of others. Many caterpillars were mimetic, imitating the leaves or flowers on which they fed, and thus obtaining protection from their enemies; others were hairy or spinose, and were probably thereby preserved from attack; whilst others again possessed neither of these modes of protection, but were conspicuous by their lively coloration. Holding that nothing in nature was without its cause, nothing without its object, and believing in the principle of natural selection or the preservation of the fittest, he concluded that this conspicuous colouring must be in some way useful to those larvæ which were endowed with or had acquired it; but in what way was it useful to them? Just as certain moths were agreeable and others distasteful to birds, so also he did not doubt that certain larvæ were agreeable and others distasteful to birds; but distastefulness alone would be insufficient to protect a larva unless there were some outward sign to indicate to its would-be destroyer that his contemplated prey would prove a disgusting morsel, and so deter him from attack. A very slight wound was sufficient to kill a growing caterpillar, and if seized by a bird, even though afterwards rejected as nauseous, its death would nevertheless ensue; the distasteful larvæ therefore required some distinctive mark, something by which they may be contrasted with and separated from the agreeable larvæ, in order that they might be freed from the attacks of birds. Brilliant coloration would be such a distinction as was required; the larvæ which were attractive to birds, when not exterminated, were doubtless preserved from extinction by other protective qualities; whilst those larvæ which were distasteful to birds, and were not protected [[p. lxxxi]] either by mimicry, hairiness, offensive smell, or otherwise, might be distinguished by their colour from those upon which birds delighted to feed. Mr. Wallace's suggestion therefore was that, as a rule, the brilliantly coloured larvæ were those which were distasteful to birds: it was on this point that he wished to collect observations and statistics, and he should be glad if any who kept birds, and particularly indigenous birds, would make experiments with different larvæ, to ascertain which were eaten and which rejected.

    Mr. Pascoe remarked that toads ate Carabidæ, notwithstanding their offensive smell; and a larva which to one species of bird would be disgusting might to another be attractive.

    Mr. J. J. Weir and Mr. M'Lachlan respectively referred to the larvæ of Cucullia and Diloba, both of which were conspicuous, but apparently free from attack.

    Mr. Bates suggested that information was also wanted as to what larvæ were most liable to be infested by Ichneumonidæ, and inquired whether amongst the British Lepidoptera there were many, or any, whose larvæ were not subject to the attacks of Ichneumons; and if any, were they conspicuous larvæ?