網頁圖片
PDF
ePub 版

as much fire and brilliancy as a diamond exposed tq the rap of the sun :, these colours, however, fade aff ter the death oi the infect, and sometimes totally disappear.

The eyes of infects are generally placed in the forehead, under the antennae: but this rule is not. •without exceptions, for some have them behind the> antennæ. In some they stand only a little out from the head, as in the grasshoppers; in some they are so much raised, that one would think them attached to , the head, only by an articulation j such are those of the small dragon-flies.

The number of eyes in infects is not uniform; the greater part have two, but there are some that have five. Besides the two large net-work eyes, a number of insects have three others on the forehead. Spiders have generally eight eyes, but they are not disposed in the same way, in all the species. Those spiders, however, must be excepted, which have long legs, and antennæ resembling the claws cf a crab, for they have but two eyes. Those of some insects resemble two hemispheres, elevated on the two sides of^ the head, consisting of a vast number of small hexagons like the cells of bees. In each of these hexagons are circles like lenses, which are so many eyes, increasing the power of that organ, to an infinite degree. By this apparatus, these insects enjoy, not only the advantages of sight, but have it probably clearer and more extensive than other animals.—This was, no doubt, necessary, on account of the rapidity of their flight, and to enable them to descry their food, while flying.

The eyes of insects are neither defended by bones, nor furnillied with eye-lids to protect them from accidents: but to make amends for this, the external

coat

coat is so hard, as to secure them from the dangers they would otherwise hare to dread. 1 imagine, that the hemispherical figure of the cornea answers the purposes of the Crystalline and other humours; and I believe that, in place of the dlfferenr coats of the eye, each hexagon receives a particular branch of the optic nerve. The eyes of other animals are moveable, but those of insects, are for the most part fixed.

There is great art, and many things remarkable ist the structure of the mouth in infects. There is almost as much diversity in the figure of this organ, as there are different species. It is broad, pointed, or long like the snout of a pig; and this last of various lengths and shapes.

Many infects have a fort of lips, not only on the upper and under side of the mouth, but at the sides. A great number have palpi at the mouth, by which, they examine tneir food, and with which they introduce it, and they likewise use them for cleaning it. These palpi have several articulations, some have tw©^ three, four, five, and even more. Some insects have only two palpi, others four. 1 he extremity of them is often round and clubbed. It is channelled in some beetles, and oblong in ethers.

We find also, in the mouth of insects, a fort of jaws or pincers, (mandibulœ,) which serve instead of teeth. These they use in comminuting their foodS or in breaking other substances. But, though these instruments are exceedingly fine and delicate, they are at the fume time very hard and strong* They are so fliarp that some can pierce the hardest wood, and make holes for themselves to live in. Those who live only on soft substances, have no use for teeth so hard or so sharp; accordingly, they are observed to be blunt in some beetles that live on rotten - » Wood, wood. These pincers, in some insects, are exceedingly smooth and mining; they pretty much resemble the spur of a cock, as may be seen in the larva of the Hemerobius. Some have small teeth on the fide of those parts which form the pincers, and opposite to one another. They are not broad like thole in man, but pointed and curved, nearly like the teeth of 3 saw. Their number is not equal. Beetles haye two; Scolopendræ three, and the larvæ of dragonT flies six. The maxillae of some insects have at their base two singular knobs, with a longitudinal recess, into which the maxillæ can be folded, like the blade of a clasp-knife. When the insect would seize any thing, and for that purpose joins the two pieces of these pincers, they do not touch, in some insects, ex^ cept at the points; in others, which have them long? er, they fold over each other.

These pincers are of great use to them; serving them not only instead of teeth, in breaking and comminuting the food they take, but for grinding many other substances, according to their necessities. It is with these they seize their prey, and hold it fast. They are likewise arms both offensive and defensive. Those which make holes in the ground, employ them in removing the things that obstruct their progress.

There are some insects of prey, (for they well de» serve the name,) which, besides these pincers, have, at the mouth a sort of claws, with which they hold their booty, as birds of prey hold theirs with their feet. Others likewise have jaws (maxilla) situated under the pincers, which are moveable, like them, but in a less degree.

I must not in silence pass over the trunk, or, a$ others call it, the tongue of inlects. Some, as the grasshoppers, carry it between their pincers. There

are are feme thzt can extend and draw It in at pleasure The Lepidopteræ roll it up very adroitlv, between two bearded bodies that conceal and protect it: others place it aloag their abdomen, where there is a little furrow formes for its reception. This trunk is not always of equal length: some have it very stiort, and some longer than the whole body. When it is viewed through a microscope, it is found to be very curiously fabricated, and, in a manner.'adapted to the way of life of the particular insect; All its parts are so disposed, that nothing is superfluous, nothing deficient. In some, it is inclosed in a sort of sheath, which terminates in a very acute point, serving to pierce the substances that contain their food. When they have done this, they open the sheath, and insert the trunk into the wound, that they may extiact the juice. It serves, therefore, as a syphon to suck the fluids they use as aliment. And besides this, it serves to prick, and to wound like a lancet. Though this trunk is so small that it can hardly be perceived, except it be with a glass, it is, nevertheless, so hard, that it can pierce, without difficulty, the hardest and thickest hide. ■

After the head, there follows the neck, the thorax and lastly the abdomen. The thorax is more or less hard in proportion as the habits of the inlect expose it to z~ greater or less degree of attrition. Those which creep into clefts a? the Cimices, ha%-e this part of the body something flat, that they may the more easily penetrate. It is more rounded in others, and some, like the Silphas, have it furnished with elevated margins, occasioning a pretty considerable corresponding furrow. The thorax in some terminates in a point behind, and that of others is blunt or rounded, as in grasshoppers. Manv have it set with hairs, and others with minute elevations which defend it from the effects of violent friction. It is surmounted

in some with a protuberance, with two angles, with a horn, or with bodies of a pyramidical oi rhomboidal figure.

In'the abdomen of insects there are many things which merit attention; and in "the first place those incisures from which these animals derive their name. These are called rings or articulations; they are formed with great art, and very much differ in appearance. Some are very close, atid look like wrinkles, others are broad and long: some -are square and some are furnished with a margin or rim; and often there is an opening discoverable between the folds. All insectsYas- may be easily imagined, have hot the same number of these rings. Some have five, some six, and some seven; all caterpillars have ten, and the aphides of the cabbage twelve. Some Scolopendræ have twenty j some forty or fifty,* and a certain larva of a Teathredo seventy-two. '->" -"

These rings are, of essential use to -insects. It is by extending and contracting these that they move. By contracting them "they defend the delicate parts of their-internal frame from the heat of the Sun, from rain and from- wind! ^-If they need heat or refreshment, they can procure either the one or the other by the dilatation of their rings which then, allow 2i> free passage to the rays of the Sun, or the frefli air. As they can dilate thenvselves' at pleasure they can receive the 'precise quantity of-either they have occasion for. """'1 ~ •'1'

. There is such diversity of figure An'she1 bodies of insects" and they are so wonderfully formed that an, exact description of them would be impossible.1 TKfe body of some, as-the spider, is of a'spherical shape, that of others as the cociriella, is hemispherical. Some are round and flat, asthe pediculi of the bat, others

U are

« 上一頁繼續 »