INSKCTA, 
331 
Some fcAV, 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 round the eye : it is frequently wanting, however, 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 Homotents (similar to the end) or the Ametobolia of Leach. 
't' Its surface is divided into several little regions or area; called the clypcus (nose 
of Kirby), the face, the front, the vertex or summit, and the cheeks. The term clypeus 
being equivocal, I have substituted for it that of epistoma or overmouth. It gives 
insertion to the labrum or upper lip. 
