ENTOMOLOGY is that branch of na tural history that treats of insects. The study of insects has sometimes been ri diculed as unworthy the attention of men of science ; for this, however, there is no just reason ; though inferior in point of magnitude, yet they surpass, in variety of structure and singularity of appearance, all the larger branches of the animal world. No one can examine with an at tentive eye the subjects of this branch of science without surprise ; the great va riety of forms, the nice adaptation of their parts to the situation in which each happens to he placed, may excite the amazement of the curious and intelligent mind The same power and wisdom which are manifested in the order, har mony, and beauty of the heavenly bodies, are equally shown in the formation of the minutest insect , each has received that mechanism of body, those peculiar in stincts, and is made to undergo those dif ferent changes, which fit it fbr its destin ed situation, and enable it to perform its proper functions. The utility of many in sects, either in their living or dead statr, as the bee, the crab, t he silk worm, co chineal insect, (see Arts, Coccus, &c.) renders them interesting and important ; i besides, tho' diminutive in point of size, they are, in regard to numbers, unques tionably the most distinguished of the works of nature ; they are to be found in every situation, in water, in air, and in the bowels of the earth ; they live in wood, upon animals, decayed vegetables, and all kinds of flesh, and in every state of its existence down to the most putrid.
The general characters by which in sects are distinguished are the following : ',hey are furnished with six or more feet ; the muscles are affixed to the internal surface of the skin, which is a substance more or less stroitg, and sometimes very hard and horny ; they do not breathe like larger animals, by lungs or gills situated" in the upper part of the body ; but by a sort of spiracles distributed in a series or row on each side the whole length of the abdomen ; tilt se are supposed to commu nicate with a continued chain, as it were, of lungs, or something analogous to them, distributed throughout the whole length of the body ; the head is furnished with a pair of what are termed antenna, or horns, which are extremely different in different tribes, and which by their st rue, ture, &c. form a leading character in the institution of the genera into which in sects are divided.
Writers on natural history formerly in cluded snails, worms, and the smaller ani mals, or animalcules, in general, among insects : these are now more properly placed among the tribe vermes, or worm like animals Late writers have extend ed this still further, and have very pro perly excluded almost the entire Linnxan order of Aptera. forming of it a distinct class, under the name of Crustacea. In sects have also been denominated blood less animals, which modern discos eries have shcwn to be contrary to fact their blood is generally a colourless sanies. Some of them, as the cimex lectularius, have been frequently used, with the mi croscope, to exhibit in a striking manner the circulation of the blood. In this in
sect, with a good glass, the vibrations and contractions of the arteries may be distinctly observed.
Most insects are oviparous ; of course, the , first state in which insects appear is that of an ovum or egg. This relates to the generality of insects, for there are some examples of viviparous insects, as in the genera Aphis, Mused, &c. From the egg is hatched the insect in its second or caterpillar state ; this second state has been usually known by the name of erica, but Linnaus has changed it to that of LARVA, which see ; considering it as a sort of masked form, or tlagnise, of the insect in its complete state. The larva of insects differ very much from each other, according to the several tribes to which they belong : those of the butterfly and moth tribe (phalana) are generally known by the name of caterpillars ; those of the beetle (scarabaus,) except such as inhabit the water, are of a,thick, clumsy form. The larva of the locust, or grass hopper, (gryllus,) do not differ very much in appearance from the complete insect, except being without wings. The lame of flies, bees, (musca, apis,) &c. are generally known by the name of mag gots, and are of thick short form. Those of water beetles (dytiscus) are of highly singular forms, and differ, perhaps, more from that of the complete insect than any others, except those of the butterfly tribe. Some insects undergo no change of shape, but are hatched from the egg complete in all their parts, and they undergo no farther alteration than that of casting their skin from time to time, till they ac quire the complete resemblance of the parent animal. In the larva state most insects are peculiarly voracious, as in many of the common caterpillars. In their perfect state some insects, as butterflies, are satisfied with the lightest nutriment, while others devour animal and vegetable substances with a considerable degree of avidity. When the larva is about to change into the crysalis or pupa state, it ceases to feed, and having placed itself in some quiet situation, lies still for several hours, and then, by a sort of effort, it di vests itself of its external skin, and imme diately appears in the different form of a chrysalis or pupa ; in this state, likewise, the insects of different genera differ al most as much as the larva. In most of the beetle tribe it is furnished with short legs, capable of some degree of motion, though very rarely exerted. In the but terfly tribe it is destitute of legs ; but in the locust tribe it differs very little from the perfect insect, except in not having the wings complete. In most of the fly tribe it is perfectly oval, without any ap parent motion or distinction of parts. The pupa of the bee is not so shapeless as that of flies, exhibiting the faint appearance of limbs. Those of the dragon-fly (libellula) differ most widely from the appearance of the complete insect ; from the pupa emerges the insect in its ultimate form, from which it never changes, nor re ceives any farther increase of growth.