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 



