Page:Cyclopaedia, Chambers - Supplement, Volume 2.djvu/796

 W O R

W O R

tion of the microfcope, and when viewed with tins afliftance there are difcovered in it parts extremely deferving our atten- tion. Phil. Tranf. N°. 469. p. 47 e.

They are of a reddifh brown colour, and of about two or three inches in length ; their thicknefs is that of a common wire ; they are compofed of a feries of membranous rings, which continually decreafe in thicknefs as they approach the extremities. Each of thefe rings has on its under part four^ five, or fix whitifh fpines, fupplying the place of legs ; and the clearnefs of the fkin gives a happy opportunity of feeing the mufcular ftrudture of the body, every ring being compofed of a great number of annular or circular muXcles, placed clofe by one another.

The head is of no determinate figure, but the creature Wretches or contracts it in length and breadth at pleaiure ; and fometimes it fhews two fmall round elevations, placed one on each fide the head, which might be very eafdy taken for eyes ; the extremity terminates in a point, that the crea- ture may be the more eafily able to pierce into the mud. The mouth is placed in that part where the head is largeft, between the two elevations before-mentioned ; this is ter- minated by two brown ftrokes, and is of the figure of a crefcent. But when the mouth is opened, it appears an a- perture of a circular figure, and is furrounded by a thick and ftrong mufcle. This mufcle is of great fervice to the animal alfo in its progrefiive motion, as it lays firmly hold of any fmooth fubftance, and the animal is then able by means of its annular mufcles to draw up its whole body to that place : At the other extremity of the body, there is. an oblong opening which ferves as an anus. There is nothing, however, more remarkable in this crea- ture, than the great artery. This veffel in caterpillars, and in many other infects, runs all along the back ; and is, by Malpighi, called a chain of hearts : But in this Worm it'is folded in different degrees, in the different parts ; and is in a manner only a long feries of folds, or doublings from one end to the other. Through thefe crooked paffages there creeps along a liquor analogous- to blood, and every mo- ment a drop of it may be traced running up from the tail, and lofing itfelf in the brain ; and it is eafy to trace this moll part of its way, by reafon of the contraction and dila- tation of the rings which follow one another fucceflively a:, it panes. Phil. Tranf. N°. 469. P.47L It feems indeed that every portion of this artery, contained in the compafs of one of the rings, is a true heart, which pufhes on to the next heart that drop of liquor which it hadjuft before received from the preceding one; and the continual repetition of the fyftoles and diaftoles in fuch a fucceffive train of hearts, is an object that may be viewed a long time with pleafurc. It is belt, of all perceived in the middle of the body, where both the rings and the hearts are largcft, and confequently the motions moft eafily diicernible. About the fifth or fixth ring from the head this artery or chain of hearts becomes a fmall and delicate filament, and from thence to the head diminifhes in thicknefs, till it is wholly loft near the mouth ; but what is very obfervable, is the fwiftnefs with which the blood is driven on in this part. Toward the tail the artery is alfo fmall, and the alternate motion of the fevcral portions of it confound themfelves to- gether, fo that the regular contractions and dilatations are not feen here, but only a fort of undulatory motion of cer- tain clouds of a fluid as it were fucceflively rolling one over another, but this with great regularity. Under every junction of the rings there are to be feen fmall veflels dividing themfelves into numerous ramifications, all thefe feem to be branches propagated from the principal artery.

All along, and immediately under this artery, is extended the channel of the inteftines ; this would not be very vifible in itfelf, but the terreftrial matter with which it is filled, ufually makes it eafily diftinguifhable : This is furnifhed like the inteftines of larger animals with different orders of inufcular fibres, which ferve to protrude the remainder of the food ; and this operation is alfo by means of the great tranfparency of the creature's fkin, eafily ken as it panes within the body.

It appears very evidently, from the contents of the ftomach, and bowels of this animal, that it receives earth or mud into its body, and has its nourishment from it. Together with this earth it alfo fometimes ncceflarily receives fome bubbles of air ; and as the air in the body of fifties ferves them very greatly in raifing and finking their bodies at plea- fure, fo in the bodies of thefe Worms the air is not without its effect, but this is generally too powerful for the crea- ture.

The bubbles of air are eafily difcerned in the body of the . creature, and when they are in any great quantity they bring up the animal againft its will, and all its ftrength will not ferve to carry it to the bottom ; but it floats on - the furfitce, till it has difcharged a part of this troublefome matter. This appears no eafy thing for the creature to do, but there is often a great ftraggle feen within its body, as It lies upon the farfjee of the -water; the bubbles bein^

driVen toward the anus, and againi forcing their way up W the head feveral times together.

Upon thefe Worms Mr. Bonet tried the experiment of cut- ing, in the manner of the operation on the polype, with fuccefs. He divided one of them into two halves, and put- ing the feparated pieces into a glafs of water; that half which had the head on it moved about, and ieemed in all refpects as well as before ; but what was much more re- markable was, that the other half which had no head mov- ed about and refted occuilonally, and feemed to perform all its operations in the fame manner as if it had one. It is obferved of the pieces into which an eel is cut, or the tail of a ferpent or lizzard, that they all move about a long time afterward ; but their motion may always be feen to be irregular and convulfive ; on the contrary, the motion of this part of the Worm feemed as regular as ever, and it made its way with tolerable fwiftneis, and that in a volun- tary manner ; the principle of life and motion feeming not to have been deftroyed in it. If it met with any obftacle in its way, it would itop and turn ; and if Jet in the fun- fhine, it was plainly affected by the heat, and became more vigorous and moved more briikiy ; and if a piece of ftick was brought near it while it lay quiet, it wouki immediate- ly {far* and make its way as fait as it could from it. Phil, Tranf. N°. 469. p. 474.

On the third day lome weeds and mud beinp- added to the water, the half which had the head immediately plunged it- felf into the mud, but the other half only hid itfelf amonc the weeds ; and at the cut end of this there was at this time very diftinctly feen a tubercle, which looked like the knot of a branch of a tree ; and at the end of a week each end was become perfect, and the two halves were two absolute- ly perfect Worms, The new head of the one, and the new tail of the other, were perfectly the fame with the old ones j and the ftomach, the grand artery, and other parts had pro- longed themfelves in a necefiary manner. After this experiment, the fame obferver cut other Warms of this fpecies into four, eight, and as far as fourteen pieces ; and moft of thefe in a few days got new heads and tails, and became perfect animals. The feafon of the year in which thefe experiments are made is of great confequence, in regard to their fuccefs.; for in fummer very few of the pieces fail of becoming perfect animals, even though one Worm be cut into near thirty pieces ^ but in winter many fail. Ibid. p. 475.

The fecond or third day after the cutting produces the new heads and tails in fummer, and in winter it is often ten or twelve days before they appear : The head always fhews it- felf firli, and lengthens itfelf continually for the firft or fe- cond week after its firft appearance, and then it ceafes to grow, having by that time arrived at a ninth part of an inch or thereabouts ; this however is not, properly fpeaking, the length of the head alone, but comprifes the rudiments of five or fix rings which are annexed to it. The tail does not begin to grow fo foon as the head, nor does it ftop its growth fo foon, but continues increafin"- in length from day to day for a long time ; and in a tew weeks the pieces of the middle part of a Worm, which were not originally above a fixth part of an inch in length, will be- come perfect Worms of two inches.

Some of the pieces of the fame Worm will grow longer and fafter than others ; and, in general, the ftnalleft or ihorteft pieces of the Worm do not grow fo quick as the longer ones.

The feveral pieces cut from different parts of the fame Worm alfo make a very different progrefs in their growth ; but, in general it appears, that thofe pieces which were cut off near the tail. grow more flovvly than thofe from any other part. The laft fragment, or that which contains the tail of the animal, grows the moft fiowly of all ; and the head-end. which might be expected to grow as remarkably quick as; this does flowly, does indeed exceed many of the parts in this particular, but is not always the very quickeft of all. There are feveral neceffary circumftances to be obfert r ed, in the progrefs of thefe operations ; the moft necefiary of all is, the allowing the creatures food; as it appears plainly that they feed on mud, there fhould always be a proper quantity of this added to the water in which the pieces are preferved, for otherwife thofe which feem to promife the faireft for becoming perfect Worms, will often very foon perifh, merely for want of nourifhment to fubfift on, before they can grow to perfection.

Dr.' Hales, in his vegetable ftatics, relates a curious experi-. ment, by which it is proved, that the bones of animals when they are offified to a certain degree, do not grow any longer, except at their extremities ; and the caie is the fame, in regard to thefe Worms ; for the old piece, which is the middle of the animal never lengthens itfelf, but the ad- dition of new rings to each end make the increafe of length in the Worm,

In all thefe pieces the liquor, which ferves as blood to the animal, is found circulating from the tail-part towards the head, in the ufual way; -and by this motion ef the blood: it.