網頁圖片
PDF
ePub 版

which could not but injure their fkin; they are likewife weapons of offence, others ftriking their enemies with them very forcibly. Lastly, 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 thefe 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 furface.

Nature has endowed fome infects with horns dif ferent from the antennæ, having no articulations. Some have but one placed on the head, and rifing straight or recurved like a hook. Some have two placed on the forehead bending to the fides cr 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 these 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. Thefe laft can by their means hold their prey as with pincers, and the former can remove any obftacle from their way,

CHAP. II

CHAP. II.

SECTION II.

OF THE INTERNAL PARTS OF INSECTS.

[ocr errors]

LET us now come to the internal parts of infects, and let us fcrutinize the inmoft receffes of their ftructure in order to penetrate into the myfteries of nature. The task is full of difficulty. Many of thofe parts are fo fmall as to escape our fight. To difcover them we muft ufe the higheft 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 these dif ficulties, however, Naturalifts have difcovered many things on our prefent fubject; thefe I'fhall detail, and add what I have learnt from my own obfervations.

If we feparate the external fkin from an infect with inftruments, or throw it into warm water, that the fkin may come away of itfelf, we fhall find that it covers many parts worthy of attention. And first in the head we difcern the brain, the substance of which is fo foft that it is not eafily examined even with a glafs. When we pierce the eyes of infects 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 refemble wrinkles in the form of rings, and are diftinctly obfervable in infects when the mul cles are inactive; but when thefe are in motion they ftretch the fibres, and make them invifible. The exceffive delicacy of the fibres in infects has prevented hitherto our difcovering whether they are enveloped with a fine membrane, like those 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 feen, even with a glafs. As they ferve to extend, and to contra&t the muscles, their ftructure muft refemble that of a wire wound round a cylinder, when that cylinder is withdrawn. They vary their motion, folding them. felves in a femi-circle, fometimes to the right, fome. times to the left, nearly like a number of fmall worms. This motion, however, is very inconfiderable, and the fibres hardly change their fituation. After thefe, the flesh of infects appears, as in other animals. There are likewife fmall veins, which, joined to the nervous and flethy fibres, compofe the muscles.

Infects are deftitute of blood, properly fo called; becaufe, the compofition of that fubitance 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. Thefe humours contain their animal fpirits, and from them infects draw their nou. rifhment. 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 fuck

[ocr errors]

1

on, without, however, reftoring it to life. This glu tinous 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 effect 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 pafs from the gullet into this ftomach, where they are digested and changed into a nutritive juice. Among quadrupeds, thofe 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 rath. Thefe animals have many parts, fo very minute, that they cannot be difcovered; may this not be the cafe with the heart? Befides, there are many fpecies, in which this organ may be diftin&tly 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

[ocr errors]

Lungs have likewise been denied to infects. But, as respiration is neceffary to every creature, and as it is carried on by means of lungs, which are found in all the other animals, we cannot doubt but infects have them likewife. They are not of the fame fize, nor the fame ftructure in all creatures; and thofe of infects are larger, in proportion, than thofe of other animals. This organ is formed in all, of little veficles, connected with one another. The air enters by the trachea, and goes out at the fame place. Infects likewife have a trachea, which terminates in their lungs, but it is not of the fame ftructure with that in other animals. In these laft, it is formed of many cartilaginous rings; in infects it is nothing but fkin, which can be dilated or contracted with eafe. The lungs of other animals have branches, which, from the vena cava, difperfe themselves through the fubftance of the lungs, in many fmaller branches. Infects have the fame, and by means of these, the air is diftributed to all their members.

In most infects, the inteftines are a little different from thofe in the other animals. The minuteness of their bodies will not admit of fo great a number. Accordingly, in many we find nothing but a tube, extending from the mouth to the vent, as may be seen in fuch as are tranfparent. It would appear, however, that, with refpect to the great gut, it is not in all of the fame figure, for the excrements of fome caterpillars are round, or cylindrical, and thofe of others have five furrows. This could not happen but from the ftructure of the rectum, which is the mould that gives the faces their figure.

Round this long tube, are many flender fibres, which answer the purpofe of veins and windpipe.

Bees have, towards the extremity of the abdomen Y

a

« 上一頁繼續 »