網頁圖片
PDF
ePub 版

those cruftaceous infects, whofe wings are longer than the elytra.

Mary fpecies of infects are covered with hairs; fometimes thefe are fo fine that they efcape the naked eye, and are vifible o: ly with a good glafs. But in others they are fufficiently obvious. They do not cover the whole body. f me have them on the head where they look like a plume of feathers, fome on the thorax, on the extremity of the abdomen, on the wings, both upper and under, and on the legs.

These hairs are of different colours which change however when the infects grow old, and are about to form their cone. They are thiniy fcattered on fome, on others thickly fet. There are alto infects where the hairs form tufts, like a brush, (fafciculi) as in the Phalana pudibunda; fome fquare, others round, often equal at top as if cut over like the egrets in the turban of a Turk, and often terminating in a point like a pencil. Sometimes the hairs are fo grofs and ftrong that they may justly be called fpines; each of thefe fpines fometimes dividing into many rigid branches, and fo fmall as to be with difficulty feen. They too are of different colours, as may be seen in the different fpecies of the thorny caterpillars and the number of their branches varies, fome having three, four or more. Their pofition is alfo very different. In fome the fpines are placed round each fing in one line as in the caterpillar of the Papilio Io; in others they are placed in two lines, not opposite to one another but alternate, and always at fuch equal diftances, that one would fay they had been measured with the greatest care; an inftance of this may be feen in the caterpillar of the Papilio Urticæ.

These hairs and fpines anfwer more than one purpofe. They preferve fome from two great friction,

.I

which could not but injure their fkin; they are likewife weapons of offence, others ftriking their enemies with them very forcibly. Laftly, in thofe that live under water, there are fome that encompass their hairs with a bubble of air which ferves them to come up more eafily to the furface. The water beetles have hairs on the belly between which there are little particles of air. When these are numerous they de fcend to the bottom with difficulty, and when they reach it, they are obliged to hold by fome fubftance to keep themselves there: but when they loose their hold, the air carries them up to the surface.

Nature has endowed fome infects with horns dif ferent from the antennæ, having no articulations. Some have but one placed on the head, and rising ftraight or recurved like a hock. Some have two placed on the forehead bending to the fides or rifing in a ftraight line. Thefe horns are either fhort, fmooth, or a little incurved like hooks, or branched like thofe of the flying ftag. Sometimes they are of equal length, fometimes one is longer than the other. There are likewife infects which have three of thefe horns rifing perpendicularly. They are not always fituated on the head, but fometimes on the fhoulders near the head. Laftly, in fome infects they are immoveable, but moveable in others. These last can by their means hold their prey as with pincers, and the former can remove any obftacle from their way.

CHA P. II.

CHAP. II.

SECTION II.

OF THE INTERNAL PARTS OF INSECTS

LET us now come to the internal parts of infects, and let us fcrutinize the inmoft receffes of their structure in order to penetrate into the mysteries of nature. The task is full of difficulty. Many of those parts are so small as to escape our fight. To discover them we must use the highest magnifiers. Befides, the eye is weakened by the continued contemplation of one object, and we feel this fenfibly when we force ourfelves to the task. Notwithstanding thefe difficulties, however, Naturalifts have difcovered many things on our prefent fubject; thefe I fhall detail, and add what I have learnt from my own obfer. vations.

If we separate the external skin from an infect with inftruments, or throw it into warm water, that the fkin may come away of itself, we shall find that it covers many parts worthy of attention. And first in the head we discern the brain, the substance of which is fo foft that it is not eafily examined even with a glass. When we pierce the eyes of ipfects with a pin there iffues out a fluid, in fome clear like water, in others red like blood. Under the fkin is the flesh. It may well receive the name fince it confifts of fib.

ro us

rous parts foft and fometimes reddifh as in other animals. The fibres are oblong parts, thin and flender like the finest thread; their ufe is to connect the other parts with one another, and to put them in motion. They resemble wrinkles in the form of rings, and are diftinctly obfervable in infects when the mufcles are inactive; but when these are in motion they ftretch the fibres, and make them invifible. The exceffive delicacy of the fibres in infects has prevented hitherto our discovering whether they are enveloped with a fine membrane, like thofe of quadrupeds. In fome infects thefe fibres are fo fhort that their length is hardly equal to the breadth of three hairs; and therefore, they are not always to be seen, even with a glass. As they ferve to extend, and to contract the muscles, their ftructure must resemble that of a wire wound round a cylinder, when that cylinder is withdrawn. They vary their motion, folding themfelves in a femi-circle, fometimes to the right, fome. times to the left, nearly like a number of small worms. This motion, however, is very inconfiderable, and the fibres hardly change their fituation. After thefe, the fiefh of infects appears, as in other animals. There are likewife finall veins, which, joined to the nervous and fleshy fibres, compofe the muscles.

Infects are deftitute of blood, properly fo called ; because, the compofition of that fubftance demands more preparation and elaboration than can be performed in a body fo fmall as theirs; but, in place of blood, they have certain vifcid humours that ferve the purposes of it. These humours contain their animal fpirits, and from them infects draw their nourifhment. However fubtile they may be, they are, nevertheless, endowed with confiderable tenacity. In confequence of this quality, the head of a fly, after being cut off, will adhere again to its body, if ftuck

on,

on, without, however, reftoring it to life. This glutinous quality of the humours enables infects to live for a time, after having been cut into two or more pieces; it prevents a rapid evaporation, it retains the humours which ftill continue to circulate for a time in the members, which would not happen without this quality. And, that this quality actually refides in the humours of infects, we may be convinced, by expofing them, when drawn from the animal, to the air, when they will fo dry, in a few minutes, as to become brittle like glue.

Infects have an artery, which is obfervable, runing along their back, and in which pulfation may be feen. The air produces in this artery the fame effe&t that blood does in circulation.

Infects eat and drink like other animals, a ftomach is therefore neceffary to them. This is nothing but an extremely thin and hollow bag. The aliments of infects pass from the gullet into this ftomach, where they are digested and changed into a nutritive juice. Among quadrupeds, those that ruminate need more than one ftomach, formed of feveral folds. It is the fame with infects; fome of them are found to ruminate, and confequently, have more than one ftomach. It is of this fort of infects that God permitted the Jews to eat. See LEVIT. CH. xi. 21. and 22.

Many perfons, not having obferved a heart in infects, have denied that they have any: but this is rafh. These animals have many parts, fo very minute, that they cannot be discovered; may this not be the cafe with the heart? Befides, there are many fpecies, in which this organ may be diftinctly feen. Laftly, the humours circulate in infects, and the arteries have a fort of pulfation; they muft, therefore, either have a heart or fomething analogous to it.

Lungs

« 上一頁繼續 »