18 Dr. John Davy's Observations on IV. Some Observations on the Excrement of Insects ; in a Letter addressed toWilUam Spence, Esq., E.R.S, Sfc. By John Davy, M.D., F.R.S., Inspector-General of Army-Hospitals. [Read January 2nd, 1854.] My dear Sir, The excrement of insects has not, 1 believe, had that attention paid to it, chemically, which the subject deserves ; especially taking into account the vast number of insect-species, how they abound, the manner in which they are diffused, or the part, as a class, which they appear to perform in the economy of nature. This too being your opinion as expressed in a letter with which you have favoured me, I am induced to collect and submit to you such results as I have obtained in a limited number of trials, with the request that you will communicate them to the Entomological Society, should they appear to be of sufficient in-terest to have the attention of that learned body. The inquiry I commenced when I was in the West Indies, between 1816 and 1849, and have since continued from time to time as opportunities have offered. I shall first bring under notice the results of the experiments made on the excrement of insects in their first stage of develop-ment, that of the larva or caterpillar. Even at the risk of being tedious, for the sake of accuracy, I must be more particular than I could otherwise wish, and shall have to describe individual in-stances. I have to express regret at the same time for my in-ability, without aid in those distant colonies, to give the specific names of the specimens which yielded the excrementitious matter examined. 1. The caterpillar of a butterfly, resembling Papilio Aphrodite, Linn., common in Barbados, in December, voided excrement in abundance when actively feeding, in the form of little green pel-lets. A certain quantity of these, dried and acted on by proof spirit, yielded a residue on evaporation, in which hippuric acid, or a matter having similar properties, was detected; thus, to men-tion one, with muriatic acid, on slow evaporation, it afforded pris-matic crystals, shooting from a centre, and which did not deli-quesce in a moist atmosphere. 2. A large caterpillar of a moth, resembling Sphinx Atropos when voraciously feeding, voided much excrement in the form of
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