attenuated and capable of being raised like a thin plate. "Its exterior face presents a net-work of hexagonal meshes, resembling that of the epidermis of plants. Each hexagon is convex, and has a conical hair in its centre, directed backwards. The rest of the surface is simply covered with small asperities, and the opposite or inferior face is concave and smooth. Each of the luminous points is thus composed of a multitude of facets, and forms an apparatus entirely similar to that which Fresnel has invented for the diffusion of light, and which bears his name. When this corneous cap is removed, the luminous matter loses a great part of its brilliancy. Every thing, in other respects, is managed with a view to increase the light to the utmost. The largest and most regular facets occupy the centre, and the smaller ones are placed at the sides, regularly decreasing in size. The hairs tend to prevent the dust settling, and the larva is possessed of a kind of anal brush, which it can employ in cleaning them."[1]
The phenomenon in question is almost confined to the Coleoptera, and among these to the families Elateridæ and Lampyridæ. About thirty luminous species of the former are known, and nearly 200 of the latter, four of which are indigenous to Europe.[2]
Nervous System.—The important and singular department of the animal economy now to be briefly considered, is rather of a simple nature in insects,
