INSECTA. 



to the animals of the preceding classes. Nearly all the remaining 

 Hexapoda have wings; but these organs, and even frequently the feet' 

 do not make their appearance at first, but are only developed after a 

 series of changes, more or less remarkable, styled metamorphoses, of 

 which we shall soon have to speak. 



The head bears the antenna, eyes, and mouth. The composition 

 and form of the antennae are much more various than in the Crus- 

 tacea, and are frequently more developed or longer in the males than 

 in the females. 



The eyes are either compound or simple; the first, according to the 

 baron Cuvier, Marcel de Serres and others, are formed: 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 ch oroides, 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, however, 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 base 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 observed, the two superior 

 jaws have been distinguished by the peculiar appellation of mandibles, 

 the others alone bearing that of maxillae or jaws; the latter are also 

 furnished with one or two articulated filaments called palpi, a character 



y 2 



