Page:Cyclopaedia, Chambers - Supplement, Volume 2.djvu/687

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it as a fingle pointed body, formed to pierce the fkin ; but Lcwenhoek difcovered that it was made up of a vaft number of pointed bodies. There is no occafion, however, for all the accuracy of obfervation of Swammcrdam, nor all the power of the magnifying glaflcs ofLewenhock, todifcover that this is a complex body ; a common fmall magnifying- glafs 5 and a careful examination, will at any time difcoverit. If a gnat be held by the corcelet between the fingers, and a little fqueezed, the fheath or cafe of the Trunk will be fre- quently feen to open itfclf lengthways on each fide, fometimes only a little way,' and at others almoft along its whole length ; and a fine glcfly reddifh filament fhews itfelf at the opening of this cafe. This filament is bent and turned inwards, and one very foon diftinguifbes that it is indeed a congeries of a great number of filaments : thefe one may eafily feparate, in fomc meafure, from one another, by means of any pointed inftrument; and very often the filament feparates of itfelf into feveral in the bending. It is plain, therefore, that the inftru- ment deft ined to pierce the (km, and fuck the blood, is of a complex ftructure ; that what we might naturally take for this inltrument, is only its cafe or fheath, and that this cafe, in- itead of a plain cylindric body, is really a compofition of two femi-cylindric ones, which have the power of feparating from one another for the animal's occafions.

The beft way to get a regular fight of the Trunk of this crea- ture, and of its manner of ufmg it, is to fiiffcr a gnat to fettle upon the hand, and not difturb him in the operation ; but with a magnifying glafs in the other band, to dbfervc all his motions. In this cafe, we may firft fee a fmall and flender point thruft out at the end of the cafe, and try feveral different parts of the fkin with this fharp inftrument ; when it has done this, it choofes that part which is moft eafily pierced ; and where there lies" a veffel underneath, capable of furnifhing as much blood as he will have occafion to fuck. As foon as he has made his choice, the wound is immediately given ; and fince the point of the compound piercer cannot be protruded fo far out of the cafe as it is neceflary it mould to ftrikc to a proper depth, the ufe of the flit in this cafe is feen ; for while the button at the end of this remains firmly applied to the orifice of the wound, where the piercer is in- troduced, and fupports that delicate and feeble inftrument from bending, the cafe opens at the flit, and its two fides bend to give room to the piercer to penetrate ; and at length, when the piercer is funk to its utmoft depth, the two extre- mities of each piece touch, and the fides arc brought clofe to- gether.

Sometimes alfo one may obferve in peculiar fpecies of the gnat kind, when they are about to ftrike the flefh, a more complex ftructure of this fheath ; for one may fee, inftead of the two antennas which all the gnats have, an appearance of four, while the creature is in the aft of fucking. It will be eafy for any one to guefs, that the fecond pair of thefe, which 60 not appear at any time, except when the creature is thus employed, are not true antennae; and on a nice examination, they appear indeed to be no other than parts of the cafe of the piercers, which, as foon as the gnat of this fpecies ftrikes the fkin, are feparated from the upper part of the cafe, and are two flender oblong bodies, of the fame length with the cafe, except that part of it which we call the button. Thefe two pieces of the cafes at this time ftand always in a parallel di- rection with the true antenna, and are very nearly of their length. Each of thefe, examined in this ftate, has the appear- ance of a regular cylinder, but, probably, in its ftate of reft, is hollowed, and of a proper Ihape, to cnclofe and furround a part of the furface of the cafe ; and this muft of neceflity be their real fhape, fince when the Trunk is in a ftate of reft, they are no other way diftinguifhable on it, than by the mak- ing it a little thicker; whereas, were they really cylindric bo- dies, as they appear in. the ftate of action of .the Trunk, they muff, when it was at reft, be (ecn in form of two prominent lines on its furface.

The feveral fpecies of gnats have great variety in their Trunks ; and in the obferving many kinds, the true ftructure of that organ in all will be m oft regularly and eafily found. Some have the cafe of the piercers only one fingle tube fplit length- wife along its upper part ; others have this flit made by the junction of two cafes, which cover clofely a great part of its circumference ; and others have the two tubes fo well adjufted, and nicely fitted to one another, that a good glafs cannot dil- cover them from the reft of the Trunk, when in a ftate of reft ; but in others this ftructure is eafily discoverable, as the extre- mity of one of them, when beft fixed, is ftill to be difcovered fomewhat feparated from the Trunk, and adorned with a pen- cil of fmall hairs, like thofc of the antenna. The male gnats, which have their antenna? feathered, are thofe which have the plumes at the extremities of thefe additional pieces of the cafe of the Trunk ; and thefe have not the beards which are found fituated over the Trunks of the other fpecies of gnats.

There is, befide all thefe, one fpecies of gnat whofe piercer has no need of the button at the end of the cafe, common to all the reft, to fupport it while it enters the flefh. This has a cafe on which it refts itfelf as on a feventh leg, froi which it darts a piercer, which, without any fupport, is of

fuificient ftrcngth to penetrate trie flefh, 2nd do its office for the animal. This fpecies of gnat has two very long beards placed above its Trunk, and terminated by an end, covered With white fcales ; what remains of thefe beards is covered with brown fcales, and the body of the gnat is brown, and the corcelet reddifh.

Tho' it is cafy to find that the Trunk of a gnat is compofed of feveral pieces, yet it is by no means eafy to fay what the number of them is. The beft microfcopes often mew the whole a fingle body, its feveral parts are fo extremely well joined ; and when they have been found to be more than one, it is very difficult yet to fay how many they are. Lewen- hoek imagined them to be four in number ; and Swatnmerdam j ^vbo had firft believed the whole a fingle filament, afterwards thought he difcovered fix pieces going to it's compofition. After feparating the piercer of the gnat wholly from its fheath, if it be cut tranfverfely near its bafe or infertion in the head, and the fection laid upon the plate of a microfcope, and there touched with an extremely fine pointed inftrument, it may be divided into four, and fometimes into five feparate pieces. Two of thefe mav often be feen to come out of a third, as out of a canal or tube : the fceming neceflity of a tube in this in- ftrument, for the fucking the blood, has made many ready to perfuade themfclvcs that they have feen one : but if we fol- low the analogy of nature in her other works, we mail find there is no abfolute neceflity for fuch an organization in this part; fince, in the gad-fly* the feveral pieces of which the piercer is compofed are of themfelves able to form a tube for the paflage of the blood.

The figures of the feveral conftituent parts of this inftrument are as difficult to be determined as their number ; thus much is certain, however, that the points of all the pieces are by no means alike, for fome are much longer than others. Out of the immenfe number of gnats that one fees in fummer, in wet places, it is eafy to determine that very few have any chance, even once in their lives, to fuck the blood of larger animals. The reft, however, are far from being doom'd to perpetual famine ; the herbs of the field afford them a fuffi- cient nourifhment; for thefe, like many other of the infect tribes, are partly carnivorous, partly otherwife, and feed equally on flefh and vegetables. Reaumur, Hilt. Infect, vol. 4. p. 580. feq*

TRUKK-A-Ianmi. See the article Manna.

TRUNSCHIBIL, a word ufed by Tournefort, to exprefs the manna Perficum, called alfo by fome Trungibin ; both evi- dently corruptions of the terenjabin of the Arabians. See the article Trungibin.

TRUSSED, in the manege. A horfe is find to be well truf- fed, in French bien gigote, when his thighs are large and proportioned to the roundnefs of the croupe. On the con- trary, a horfe with thin thighs, that bear no proportion to the breadth of the croupe, is faid to be illtrufcd.

TRUTTACEOUS, in zoology, the name of a genus of fifties of the trout kind, which are diftinguifhed from all other fifties by a fmall fat fin, which they all have near the extremity of the back, and which has no rays or nerves. Of the fifh of this genus, fome live only in frefh waters, never entring the fea or fait rivers : others frequent both the frefh and fait wa- ters, and are therefore called anadromi or catanadromi? Thefe leave the frefh waters while young, and go into the fait wa- ters to feed and grow, and again return into the frefh rivers at the time of their full growth and (pawning, that their ofF- fpring may have the fame advantages themfelves have had, of being hatched into life in frefh water.

The iruitaceous fifties are divided into two orders, thofe which have, and thofe which have not teeth. Of the edentulous kind, or fuch as have no teeth, are the lavaretus, ferra, thy- mallus, oxyrynchus, and albula; and of the toothed kind, are the falmo, umbra, trutta, carpio, &c. In diffection, the trutiaceous fifties have all apophyfes to the pylorus, and are all a high-taftcd and fine fet of fifh for the table. Ray's Ich- thyography, p. 182.

TRY (Cycl.) — Try, at fea. A fhip is faid to try, when fhe has no fails but her main-fail aboard ; when her tacks are clofe aboard, the bowlings fet up, and the fheets haled clofe aft ; when alfo the helm is tied clofe down to the board, and fo fhe is let lie in the fea. And fometimes when it blows fo hard that they cannot maintain the main-fail, as they fay, that is, cannot bear it out, they make her lie a Try under a mi (Ten -fail only.

TRYBLION, a word ufed by the old medical writers, to ex- prefs the pot or difh in which the medicines ufed in fumiga- tions were placed at the time of ufe.

TRYCHNUS, in botany, the fame as Stryclmus, the name of the nightfhade. The Greeks called it r^x^, and the Latins, as well as themfelves, often left out the initial <?, as they do in many other words j thus they write milax for jhiilax, marag- dus for fmaragdus, &c.

Pliny ufes the word Trychnos as the proper name of the plant; and Diofcorides, willing to diftinguifh the mad nightfhade from the fleepy nightfhade, which are the two poifonous kinds, fo called from their different effects, calls the one Trvcbnos and the other Strychnos. But this is a trivial dif- ference in the name, and would never be efteemed any dif- ference