342 INSECTA. 



the baron Cuvier, Marcel do Serres and others, are fornried: 1, of 

 a cornea, divided into numerous little facets, which is so much the 

 more convex, as the insect is more carnivorous; its internal surface 

 is covered with an opaque, and variously coloured, but slightly fluid 

 substance, usually, however, of a black or deep violet hue; 2, of a 

 choroideSj fixed by its contour and edges to the cornea, covered 

 with a black varnish, exhibiting numerous air vessels, arising from 

 tolerably large trunks of tracheae in the head, whose branches form 

 a circular trachea round the eye: it is frequently wanting, how- 

 ever, as well as the choroides, in various nocturnal insects; 3, of 

 nerves arising from a large trunk, proceeding directly from the 

 brain, which then opens, forming a reversed cone, the bas^ of which 

 is next to the eye, and each of whose rays or threads traversing the 

 choroides and lining matter of the cornea, terminates in one of its 

 facets; there is no crystalline nor vitreous humour. 



Several, besides these compound eyes, have simple ones, or ocelli, 

 the cornea of which is smooth. They are usually three in number, 

 and are disposed in a triangle on the top of the head. In most of 

 the Aptera and in the larvae of those that are winged, they replace 

 the former, and are frequently united in a group; those of the 

 Arachnides seem to indicate that they are fitted for the purpose of 

 vision. 



The mouth of the hexapodous insects is generally composed of 

 six principal parts, four of which are lateral, are disposed in pairs, 

 and move transversely; the other two, opposed to each other in a 

 contrary direction, occupy the space comprised between the former: 

 one is placed above the superior pair, and the other beneath the 

 inferior. In the triturating insects (broyeurs), or those which feed 

 on solid matters, the four lateral parts perform the office of jaws, 

 the other two being considered as lips; but, as we have already ob- 

 served, the two superior jaws have been distinguished by the pecu- 

 liar appellation of mandibles, the others alone bearing that of maxilla; 

 X)r jaws; the latter are also furnished with one or two articulated 

 filaments called falpi^ a character never exhibited, in this class, by 

 the mandibles. Their extremity is often terminated by two divisions 

 or lobes, the exterior of which, in the Orthoptera, is called the 

 galea. We have already said that the upper lip was called the 

 labrum. Tlie other, or the labium properly so styled, is formed of 



