OF INSECTS. 
173 
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 regu- 
lar 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/’* 
The phenomenon in question is almost confined to 
the Coleoptera, and among these to the families 
Elateridse and Lampyridse. About thirty luminous 
species of the fonner are known, and nearly 200 of 
the latter, four of which are indigenous to Europe.t 
Nervous System. — The important and singular 
department of the animal economy now to be briefly 
considered, is rather of a simple nature in insects, 
* Lacord. Intro, h V Ent. II. 147. 
-f- Examples of both will be found figured and described 
in our Coleopterous Vol. p. 161-172. 
