2. HEMIPTERA. These have also four wings; but the elytra are different, being half crustaceous, half membranaceous: the wings do not form a longitudinal suture, but extend the one over the other, as in the gryllus, grasshopper, &c.
3. LEPIDOPTERA. Those which have four membranaceous wings covered with fine scales, appearing to the naked eye like powder or meal, as in the butterfly and moth.
4. NEUROPTERA. These have four membranaceous transparent wings, which are generally reticulated, the tail without a sting, as in the libellula, or dragon fly.
5. HYMENOPTERA. These, like the preceding class, have four membranaceous naked wings; but the abdomen is furnished with a sting, as in the bee, wasp, ichneumon, &c.
6. DIPTERA. These have only two wings, and are furnished with halteres, or poisers, instead of under wings, as in the common house fly, gnat, &c.
7. APTERA. These are distinguished by having no wings, as in the spider, louse, acarus, &c.
Insects are farther distinguished from other animals by the wonderful changes that all those of the winged species without exception, and some which are destitute of wings, must pass through, before they arrive at the perfection of their nature. Most animals retain, during their whole life, the same form which they receive at their birth; but insects go through wonderful exterior and interior changes, insomuch that the same individual, at its birth and middle state, differs essentially from that under which it appears when arrived at a state of maturity; and this difference is not confined to marks, colour, or texture, but is extended to their form, proportion, motion, organs, and habits of life.
The ancient writers on natural history were not unacquainted with these transformations, but the ideas they entertained of them were very imperfect and often erroneous. The changes are produced in so sudden a manner, that they seem like the metamorphoses recorded in the fables of the ancients, and it is not improbable that those fables owe their origin to the transformation of insects. It was not till towards the latter end of the last century that any just conception of this subject was formed; the mystery was then unveiled by those two great anatomists Malpighi and Swammerdam, who observed these insects under every appearance, and traced them through all their forms; by dissecting them at the time just preceding their changes, they were enabled to prove that the moth and butterfly grow and strengthen themselves, that their members are formed and unfolded under the figure of the insect we call a caterpillar, and that the growth was effected by a developement of parts; they also shewed that it is not difficult to exhibit in these all the parts of the future moth, as its wings, legs, antennæ, &c. and consequently that the changes which are apparently sudden to our eyes, are gradually formed under the skin of the animal, and only appear sudden to us, because the insect then gets rid of a case which had before concealed its real members. By this case it is preserved from injuries, till its wings, and every other part of its delicate frame are in a condition to bear the impulse of the sun, and the action of the air naked; when all the parts are grown firm, and ready to perform their several offices, the perfect animal appears in the form of its parent. Though these discoveries dissipated the false wonders of the metamorphoses that the world before believed, they created a fund of real admiration by the discovery of the truth. These transformations clearly prove, that without experience every thing in nature would appear a mystery; so much so, that a person unacquainted with the transformation of the caterpillar to the chrysalis, and of this to the fly, would consider them as three distinct species; for who, by the mere light of nature, or the powers of reason unaided by experience, could believe that a butterfly, adorned with four beautiful wings, furnished with a long spiral proboscis or tongue, instead of a mouth, and with six legs, proceeded from a disgusting hairy caterpillar, provided with jaws and teeth, and fourteen feet? Without experience, who could imagine that a long white smooth soft worm hid under the earth, should be transformed into a black crustaceous beetle? Nor could any one, from considering them in their perfect state, have discovered the relation which they bear to the several changes of state, and their corresponding forms, through which they have passed, and which are to appearance as distinct as difference can make them.