Page:Cyclopaedia, Chambers - Supplement, Volume 1.djvu/934

 I N S

iNS'C'HI, or Inschi Km, in the materia medica, a name given by fome authors to the common ginger.

INSECTS {Cycl.) make one of the clafles of animals, the characters of which are, that their body is covered with a fort of bony fubftance inftead of (kin, and their heads are furnifhed with antennae, called horns. Linnai Syftem Nat.

P- 8 3- Eyes of Insects. The bounty of nature in giving eyes to thefe fmall animals is amazing ; they have often befide the reticular large eyes, which make fo confiderable a part of the bignefs of the head, other fmall ones placed triangularly above or below them. Thefe reticulated eyes however are the moft amazing of all, and are in a manner common to the whole lnfed world. Many authors have defcribed them, but none fo accurately as Reaumur in his hiftory of Infects. He has given his defcriptions from the eyes of the butterfly kind, but they equally ferve as the general defcriptions of all the reft. Reaumur's Hift. Infect, vol. i. P. I. p. 261. Thefe reticulated eyes always form a part of a fphere : This in fome fpecies is a larger, and in others a fmaller portion ; and confequently fome are more, and others lefs prominent, and they are larger or fmaller in proportion to the fize of the head in the different fpecies. The externa] covering of thefe eyes, which by its pofition and ufes may be called the cornea, has a fort of glofs on it, which often fhews all the rainbow colours, as it is differently turned to the light : And the co- lour that makes the bafis of thefe, and appears the general colour of the eye in a common light, is black in fome fpecies, brown in others, and in others grey. Sometimes a change- able affemblage of feveral colours ferves in the place of a fimple one, even in this view. A view of thefe eyes by the naked eye fhews us that their furface is not even or fmooth, but dotted all over ; but when we bring them before the mi- crofcope, the ftructure is found to be truly wonderful. The whole furface then appears to be reticulated, and the feveral mefhcs of the net all regularly of the fame fize. The middle of each mefh is not empty but filled with a globular body, the furface of which ftands up above the level of the reft, fo that the whole cornea or external furface of the eye, appears no other than a multitude of little globular bodies, ftuck into a fubftance proper to retain them in their proper places ; and the matter in which they are placed forms a rectilinear figure furrounding them, which is fquare in fome fpecies, and hex- angular in others. The whole cornea may be therefore compared to a glafs cut into a number of convex faces ; or in properer terms, the cornea may be faid to be compofed of a prodigious number of cryftallines, arrang'd in a beautiful order clofe together. The number of cryftallines that go to the formation of one of thefe eyes, is fcarce to be conceiv'd; but as different authors have been at the pains of counting them in different Itifefts, and as our own obfervations may at any time evince the truth of each calculation, there is no doubt of the reality of them. Lewenhoeck counted 31S1 in the fingle eye of a beetle, and Scoo in the eye of a fly. Mr. Puget, an author of great accuracy, counted 17325 in the'eyc of a butterfly; and Malpighi, from the moft careful obfervations, and analogy with the parts of other animals, declares each of thefe to be a diftinct and feparate eye ; fo that inftead of the vulgar opinion of a butterfly's having no eyes, we find it has in reality no lefs than 34650. And the fucceeding obfervations of the curious in microfcopes, have found that every one of thefe eminences in the cornea of In- fetls, has all the neceffary parts, and performs all the offices

I N S

of an

eye.

The accuracy of the Abbe Catalan, and after him of feveral others, has yet gone farther in the obfervation of thefe eyes. They have pick'd out a fingle one from the net, and making it clean, have examined and found it to have all the proper- ties of an eye. The whole cornea may alfo be cut off, and wafh'd clean on the infide by means of a foft pencil and warm water ; and when perfectly clean'd in that manner, it be- comes beautifully tranfparent, and if held up in the apparatus of a microfcope, and pointed againft any object, it multiplies and diminifhes it in fize in a manner not to be defcribed, and with a beauty not cafily conceiv'd. A fingle foldier viewed thro* it, gives the appearance of an army of pigmies ; and the arches of a bridge are fo multiplied in number, and ap- pear fo elegantly difpos'd over and about one another, as that they make an object of beauty fcarce to be defcrib'd. The light of a candle viewed thro' it, is feen elegantly multiplied into an immenfe number of candles ; and indeed none of the common multiplying glaffes, nor any that can be made by art, can ever fhew fuch a number of faces. Reaumur's Hift. Inf. vol. 1. P. 1. p. 267.

The cxiftence of thefe numerous cryftallines is then a point no longer to be doubted, and authors have gone yet farther in their obfervations and gueffes concerning them. Lewen- hock difcovered the bundles of optic nerves which ferve thefe fmall lenfes ; and Reaumur fuppofes thefe nerves to fupply the place of all that is wanting behind the lenfes, for the organifation of an eye compleat for vifion; and he thinks that the tunica choroides being of different colours indifferent InfcJs, is the reafon why we fee their eyes of different co- lours.

We ouvfelves fee objects with two eyes at once, and yet thofe 1 objects appear fingle to us ; and the fame mcchanifm that makes us fee them fo, may make the Infect clafs fee them fingle alfo, tho' they fee them thro 5 many thoufands of eyes at once.

The ufes of thefe numerous eyes to thefe fmall animals are obvious j and as they are in continual want of food, and in continual fear of enemies, it is extremely proper that they fhould be well prepared to be aware when either the one or the other is near. It has been fuppofed by many naturalifts, that the eyes in thefe corneae are fo fmall and convex, that they can only ferve the creature to fee very near objects, and muft magnify them extremely ; but obfervation fhews that a fingle eye of thefe held in the focus of a microfcope, ferves with the lens in that apparatus to fee diftant objects dimi- nifhed. We alfo know, that two convex lenfes of great power, may be fo combin'd as to fhew diftant objects very diftinct, and diminifhed in fize, not magnified ; fo that we find fuch eyes may be made to ferve fuch purpofes, and, we have no reafon to doubt, but that what we are able to do by art, is much better done in them by nature. Among all the naturalifts who have been converfant in mi- crofcopes, none could mifs obferving and admiring fuch a wonderful ftructure and organifation as that of thefe parts ; all have obferv'd them, but lome have been of opinion that they are not really eyes ; there is however no doubt, but that parts fo beautifully and nicely organis'd, muft ferve to fome ienfation, and to what other fenfe except that of feeing, can their frame and ftructure feem to point ? Mr. De la Hire was one of the firft who doubted whether thefe reticulated parts were eyes ; fur obferving that flies had belide thefe three lucid points in the front of their heads, he concluded that thofe points were eyes, as indeed they certainly are ; and taking it for granted that three eyes of this kind were enough for fuch an InfeEij he concluded that the other reticular bodies were not eyes ; but it having been fmce obferved, that all Infecli have not thefe other fmaller eyes difcovered by Mr. De la Hire, and particularly that the whole butterfly clafs wanted them, and therefore that fomething elfe certainly fupplied their place, and what fhould do that but thefe reticular eyes? A fly is indeed furprizingly furnifhed by nature with the or- gans of fight; it has two large and reticulated bodies, each of which contains many thoufands of eyes ; and befide thefe, has not barely three, but has twelve, fifteen, or more of thefe fingle brilliant eyes, placed in feveral parts of its head. The fpider has alfo a great number of thefe lucid or brilliant fingle eyes, and they are placed in different parts of the head, and are of different fizes, fo that it fhould feem as if nature has furnifhed them with different eyes, fuited to different purpofes, fome being of ufe to fee near objects, and others the more diftant; and that thefe creatures inftead of eyes deftined like ours for the fame purpofes, had microfcopes and telefcopes always in readinefs for their feveral occafions. In the butterfly clafs, there are feveral which have a great number of hairs growing on the reticulated bodies, placed on the fides of the head ; thefe hairs have been urged by thofe who w r ere unwilling to allow the reticulated bodies to be eyes, as a great objection to the received opinion of their being fo : But the anfwer is eafy, that tho* if each of thefe reticulated bodies was a fingle eye, the vifion muft neceifa- rily be troubled by fuch a number of hairs growing in the midft of them ; yet as they appear to be in reality each com- pos'd of a-vaft multitude of eyes, thefe hairs may perhaps ferve only in the office of eyelids to them, and that their breaking off a part of the rays of light may be no injury to vifion, but even neceffary to eyes of fo tender a ftructure. Reaumur's Hift. Infect, vol. 1. P. 1. p. 273. Anatomical ufe of Insects. The lnfed world affords us nu- merous ufes, and thofe many of them fuch as no one would at firft thought imagine, and which no other operations or operators could fo well effect. In the minutiae of anatomy, where knives cannot be introduced, the maggot or the ant may be employed with great fuccefs. Skeletons of foetus's have been prepared by burying them In an ant-hill, and that in fo accurate and perfect a manner, that all who have ken them, have admired by what means they could be fo nicely finifhed ; and the fecret of the great Ruyfch, by which he cleared away the parenchymatous fubftance from his vnfcular preparations, was of this kind. After injecting the veffels of any part with wax, all that remained to the compleating thefe preparations, was the taking off the parenchymatous or flefhy matter from between and among them. Other anato- mifts of his time did this by the knife, or by maceration in water, and other liquors ; but it appeared a fort of magic to them, that his were always not only much fooner executed, bur. to a greater nicety and perfection than theirs ever poffibly could be. His method was only to put a number of the common flefh-eating maggots, to the fubftance; and thefe regularly eat away all the flefh, their heads getting into crevices which no inftrument could reach, and the whole fubftance of the injection remained unhurt, as their foft bodies could glide between its niceft parts without injuring them ; and the wax being no food for them, was in no dan- ger of being eroded, even in its fmalleft pieces. The feveral

fizes