INSECT*. 331 



Some few, and always apterous Insectes, such as the Myriapoda, 

 approximate to several of the Crustacea, either in the number of the 

 annuli of their body and in their legs, or in some points of analogy 

 in the conformation of the parts of the mouth ; but all the others 

 never have more than six legs, and their body, the number of whose 

 segments never extends beyond twelve, is always divided into three 

 principal parts, the head, trunk, and abdomen. Among the latter 

 Insects, some are found without wings, that always preserve their 

 natal form, and merely increase in size and change their skin *. In 

 this respect they bear some analogy 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 f bears the antennce, eyes, and mouth. The composi 

 tion and form of the antennae are much more various than in the 

 Crustacea, 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 

 choroides, fixed by its contour and edges to the cornea, covered with 

 a black varnish, exhibiting numerous air vessels, arising from tolera- 

 bly large trunks of tracheae in the head, whose branches form a cir- 

 cular trachea roimd the eye : it is frequently wanting, hoAvever, as 

 well as the choroides, in various nocturnal insects ; 3, of nerves aris- 

 ing 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, the cor- 



* My Homotencs (similar to the end) or the Ametoholia of Leach. 



t Its surface is divided into several little regions or arere called the chjpeus (nose 

 of Kirby), the /ace, the/>-on/, the vertcv or summit, and the cheeks. The term clypeus 

 being equivocal, I have substituted for it that oi epistoma or overmouth. It gives 

 insertion to the labrum or upper lip. 



