MM. Humboldt and Bonpland discovered, in South America, a species, probably of the same genus, which attacks man himself. The perfect insect is about the size of our common house-fly (_Musca domestica_), and the bump formed by the grub, which is usually on the belly, is similar to that caused by the ox breeze-fly. It requires six months to come to maturity; and if it is irritated it eats deeper into the flesh, sometimes causing fatal inflammations. Grub Parasite in the Snail. During the summer of 1829, we discovered in the hole of a garden-post, at Blackheath, one of the larger grey snail shells (_Helix aspersa_, Muller), with three white soft-bodied grubs burrowing in the body of the snail. They evidently, from their appearance, belonged to some species of beetle, and we carefully preserved them in order to watch their economy. It appeared to us that they had attacked the snail in its stronghold while it was laid up torpid for the winter; for more than half of the body was already devoured. They constructed for themselves little cells attached to the inside of the shell, and composed of a sort of fibrous matter, having no distant resemblance to shag tobacco, both in form and smell, and which could be nothing else than the remains of the snail's body. Soon after we took them, appearing to have devoured all that remained of the poor snail, we furnished them with another, which they devoured in the same manner. They formed a cocoon of the same fibrous materials during the autumn, and in the end of October appeared in their perfect form, turning out to be _Drilus flavescens_, the grub of which was first discovered in France in 1824. The time of their appearance, it may be remarked, coincides with the period when snails become torpid. (J. R.) In the following autumn, we found a shell of the same species with a small pupa-shaped egg deposited on the lid. From this a caterpillar was hatched, which subsequently devoured the snail, spun a cocoon within the shell, and was transformed into a small moth (of which we have not ascertained the species) in the spring of 1830. [Before concluding the account of the parasite insects, it will be necessary to mention two of our British Ichneumonidæ, which not only deposit their eggs in the larvæ of other insects, but make for themselves cells of very beautiful structure. In the accompanying illustration are shown the cells of one of our commonest and most useful ichneumonidæ (_Microgaster glomeratus_), together with the insect itself. At Fig. 1_a_ (p. 438) is shown the little insect of the natural size, and the same is given at 1 much magnified. This creature lays its eggs in the body of the cabbage caterpillar, forty or fifty eggs being deposited in the same larva. They soon hatch into little transparent grubs, which lie under the skin, and live on the fatty parts of the caterpillar, which continues to grow, and seems to thrive, whereas its bulk is largely made up of the ichneumon larvæ.