We are indebted to M. de Quatrefages for some interesting experiments on the termites of La Rochelle. Not only has the learned naturalist helped to make known to us the habits of these dark-loving insects, but he has also told us how to destroy them. Different substances have been tried in vain to stop these terrible ravages--essence of turpentine, arsenical soap, boiling lye, &c. M. de Quatrefages had recourse to gaseous injections. He tried successively binoxide of nitrogen, nitric acid, chlorine and sulphurous acid; chlorine, above all, fully answered his hopes. With pure chlorine he killed the termites instantaneously; mixed with nine-tenths of air, he suffocated them in half an hour. "For attacking the termites," says M. de Quatrefages, "one ought to choose by preference the period of their reproduction, so as to destroy the pregnant females. It is probable that, like their exotic congeners, the termites of France will endeavour to defend themselves by walling up the interior of their galleries at the first signs of an attack. The operator must then act with a great deal of promptitude, and direct the apparatus as much as possible into the very centre of their habitation, where the galleries are the broadest and the most numerous. "With whatever care one acts, and whatever may be the success of a first attempt, it seems to me impossible to destroy in one campaign all the termites of a locality. In this, as in all operations of the same kind, a certain amount of perseverance is necessary, especially if it is in a town or in a country infested by them to a very great degree; in that case one will be forced to repeat the operation from time to time. When, on the contrary, the termites are already cantoned, it seems to me that the success ought to be lasting. This is fortunately the case at La Rochelle; and by knowing how to profit by it, one may doubtlessly prevent the spread of these pests, which at one time or another, may attack the whole town."[116] [116] "Mémoires sur la destruction des Termites." _Annales des Sciences Naturelles_, 3e série, tome xx., p. 15. In 1864 the Lords of the English Admiralty addressed an inquiry to the Entomological Society of London, on the best means of preserving wood from the attacks of the Indian termites. In answer to this inquiry, the Entomological Society recommended many processes: the injection of quicklime or of creosote, the application of arsenical soap, &c. But it does not appear that these processes are infallibly efficacious, nor, above all, easy to employ. [Illustration: Fig. 384.--Larva of Perla bicaudata.] [Illustration: Fig. 385.--Larva of a Nemoura.] [Illustration: Fig. 386.--Perla marginata (larva).]