Different naturalists have attempted to arrange insects into families and gene ra, particularly the celebrated Linnaeus, whose arrangement may be thus explain ed. He has formed them into seven families or orders, composing his sixth class of animals, Insects : he defines an insect, a small animal, breathing through pores on its sides, furnished with movea ble antenna and many feet, covered with either a hard crust or a hairy skin. As in troductory to the distinguishing marks of the orders and genera, it will be ne cessary to enumerate and explain the terms given to the different parts, and the most remarkable of the epithets applied to them by entomologists. The body is divided into head, trunk, abdomen, and extremities.
1. Caput, the head, is in insects, as well as in the vertebral animals, the principal repository of the senses, and contains that most important organ, the brain : externally it is furnished with eyes ; stem mata ; antenna ; clypeus ; vertex ; mouth; front ; gula.
Eyes, are situated on each side of the head, and differ much in form and colour in the different insects, and may be con sidered amongst the most surprising of nature's works ; they are not, as might be at first supposed, mere hemispherical bodies of plane and simple surfaces, but examination proves them to be composed of an immense assemblage of highly wrought hexagonal fascets, each furnish ed with its proper optic nerve, retina, &c. complete for vision : the number of these fascets differs in different species ; in the eye of the common fly 8,000 have been counted, and in that of the libellula or dragon fly about 12,000.
Stemmata are hemispherical bodies placed upon the vertex, and are suppos ed to perform the office of eyes. The antenna are two articulated moveable processes, placed on the head ; they are either, 1. Setacea, setaceous, i. e. like a bristle, when they taper gradually from their base to their point. 2. Clavatx, cla vated, club.shaped, when they grow gradually thicker from their base to their point. 3. Filiformes, filiform, i. 0. thread shaped, when they are of an equal thick ness throughout the whole of their length. 4. Moniliformes, moniliform, i. e. of the form of a necklace, when they are of an equal thickness throughout, but formed of a series of knobs, resembling a string of beads. 5. Capitatz, capitate, when they grow thicker towards the point, and terminate in a knob or head. 6. Fis
siles, fissile, i. e. cleft, when they are capi tate, and have the head or knob divided longitudinally into three or four parts or lamime. 7. Perfoliatx, perfoliated, when the head or knob is divided horizontally. 8. Pectinate, pectinated, i. e. resembling a comb, when they have a longitudinal series of hairs projecting from them, in form of a comb. 9. Barbatm, barbed, when they have little projections or barbs placed on their sides : they are either longiores, longer than the body ; bre viores, shorter than the body ; or, tyre diocres, of the same length with the boa) sier has shewn that the organs of hearing are placed at the base of the antenna 1., the crustacea, such as crabs and lobsters, and from analogy many na turalists have supposed them to be simi larly situated in the true insects; this may probably be correct, but it has not yet been proved, and must not therefore be assumed.
Clypeus, the covering of the head in the beetle tribe ; it extends from the eyes, often projecting over the mouth.
Vertex, the top of the head above the front.
Front, this term is applied to the an terior part of the head of most insects, and is analogous to the clypeus of the beetles.
Cola, throat, underneath the head, sup porting the lip.
Mouth, is situated in the head, rarely in the breast, and affords so great a variety of characters, that the celebrated Fabricius founded upon them his entire system of arrangement ; the principal and most obvious parts are, the palpii, mandi hula, labrum, labium, ligula, maxilla, and gale e.
Palpi, or feelers, are articulated fila ments of different forms, sometimes re sembling antenna, placed in the mouth, either on the jaws or lip ; they are two, or four, or six, in number, and are either anterior, intermediate, or posterior, or, according to Latreille, labial or maxillary. Considered in relation to those parts upon which they are situated, they generally furnish good generic characters.
andibula, mandibles, two horny curv ed pieces, placed one oil each side of the mouth, moving laterally, and used by the insect either to seize its food, or as wea pons in its combats.
Maxilla, jaws, two horny or submem• branaceous pieces, placed one under each mandible, generally ciliated with hair, or dentate on the inner side, and always pal pigerous in those insects that have more than one pair of palpi.