Page:Cyclopaedia, Chambers - Supplement, Volume 2.djvu/747

 URT

Meceflary parts of an animal could not be found in fuch a piece of one,

Though the generality of thefe animals are of the fimple colour ofa jelly, there are fome of a grecnifh calf, and others which ■have a broad band of a beautiful purple round their extremity ; and fome are beautifully fpotted with brown. Their figure is very well expieffed by that of the head of a large mufhroom ; their upper furface is convex in the fame manner, and this convexity is greater or lefs in the different kinds, as' it is in the different fpecies of mufhrooms ; all that is to be obferved on this convex furface, is, that it has feveral little protuberances on it, fhaped like (o many nipples, and placed in an irregular manner ; thefe are of the fame colour with the reft of the body ; but though there is nothing more to be feen on this furface, the under, or concave one, gives proof enough of a regularly organized body. The edge is very thin, and cut in feveral places ; and juft within that there appears a great num- ber of concentric circles, which cover the reft of the furface. Thefe are not all complete ; however, thofc which are near the center, are divided into fixteen arcs, and thofe more diftant into eight. Thefe reparations in the circles arc made by certain tubes, which are always full of water, which they can, at pleafure of the animal, communicate to other verv final! and fine tubes, placed between the circumferences of funic two of the circles, Thcfc fmali tubes arc of great con- fequencc to the well-being of the animal, and they are known to be tubes by their figure, when full, and arc cafily proved to have communication with thcfc other refer voirs, by the pref- fing the larger, which always fends the water into thcfc Smaller ones. The large veffcls, which go from the center to the circumference, and thcfc finall circular ones feem, in fome meafure, to referable in their ofEce the veffefs of larger animal bodies ; and this water contained within them, to he a liquor elaborated there, and analogous to blood, which fills out and difiends the very fine and final 1 fulid parts, of which this animal's body is compofed. If one of thefe animals be dried in the fun in hot weather, there remains nothing of it but a fubftance like a thin parchment ; but if one of them be boiled in water, it docs not diflolve away as might have been expected, but only regularly decreafes in fize ; and when it has become of about one fourth of its natural bignefs, it there flops the decreafe, and continues nearly of that fize, and af- ter that will not melt away upon the hand. Near the end of the ftrait tubes, all the animals of this fpecies are divided into fqur parts, by four bands or columns, for they are round in fome, and flat in others. Thefe are fumetimes raifed almoff. perpendicularly on the bafe ; fometimes they make an acute angle, and they all join at length to a round trunk of about their own length; this trunk is ofacylindric figure, and is divided into eight branches. In the fpace con- tained under the four columns, there is a large canal formed by a thick membrane,' which fcems the only folid fubftance in the animal ; this membrane is folded into a fort of purfe, and forms a fort of canal, which becoming round near the bafe of the columns, takes the fame figure which a ribband would have, if turned round the four arms of a large and regularly fhaped croft. This large canal is full of a yellowifh glutinous liquor, and it ufually gives one or two branches to each of the columns. Thefe four colums terminate, as before obferved, in a trunk, which then divides into eight branches, and their route may be further traced through the whole body of the ani- mal, as they contain the fame yellowifii liquor with this large veflel, which is every where diltinctly feen, as being very different from the reft of the body in colour. All the creatures of this fpecies, which we fee thrown upon the fhores, are found lifelefs and without motion ; but there is nothing wonderful in that, becaufe the violent fhocks and blows which they muft have received, in being dabbed againft the rocks or fands by the waves, are enough to kill fo tender an animal. One proof that thefe animals once lived, is, that all thofe which we find about the fhores are heavier than the water, and fink to the bottom, whereas all thofe feen out at fea, fwim upon the furface ; and this could not be the cafe in regard to any fubftance heavier than water, unlefs kept up by fome voluntary motion. This motion Mr. Reaumur has ob- ferved -to be a reciprocal contraction and dilatation of the whole body, in the manner of a fyftole and diaftole. In the contraction it elevates the convexity of the hodv, and in the dilatation it makes it more flat, and by continually repeating thefe motions, it keeps above water as a man does by fwim- ming. Mem. Acad. Par. 1710.

Urtica Marina, the Sea-Nettle, in botany. See the articles Lamium and Archangel.

Urtica Marina, in zoology, the name of a remarkable genus of fifties, fo called from their affecting the fkin on touching them, with a painful fenfation like that of the flinging of net- tles, Thefe are an animal of the loweft clafs, and have by many been reckoned among thofe creatures called zoophytes, or plant animals, as fuppofed to partake of the nature of vege- tables and of animals. Some of the fpecies of this fifti are found loofe upon the fmooth fhores, and fome fixed to the rocks which are always covered with water. This has given birth to a diftinction of them into two claiTes, which is as 3

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old as Anftotle ; thofe of the one being fuch as move in the open fea, and thofe of the others fuch as are fixed to rocks and were fuppofed always to remain immoveably in the fame place. The accurate Mr. Reaumur has obferved, however, that even thefe laft have a power of a progreffive motion, and arc not doomed to an eternal refidencc on the fame fpot The motion of thefe creatures is fo flow, that it might eafily pafs unobferyed by lefs accurate obfefvers ; this gentleman com- paring it to that of the hour-hand of a clock, and adding, that a journey of an inch takes them up commonly between one and two hours.. He obferves alfo, that many of the fpe- cies have no property of flinging; of caufmg any painful fen- fation on the fleih. Ariftotle and Pliny, who were both in- clined to make thefe creatures of a middle nature between plants and animals, yet differ in their accounts of them ; the former affirming that they have no anus or exit for their excre- ments, and the other allowing them an extremely fine tube or pipe for that purpofe. What Pliny fecms to mean by this pipe, muft he one of the horns of the creature ; but the mat- ter it difcharges from that, has nothing of the appearance of excrements,' being mere clean water. "Senfation; a power of eating and digefting food," and locomotion, being certainly fufneient characters of animal life, and this creature being evidently pofleflcd of them all, there is no room to doubt its being as truly and properly an animal, as a whale or an ele- phant.

Thefe creatures occafionally change their bodies into fomany different forms, that there is no giving any defcriptii .n of their fi- gure. The molt natural and 'general ihapej feems that of a trun- cated cone, the bafe of which is applied to the rock 5 but this bafe is often round, often elliptic, and often of a perfectly irregu- lar figure. This bafe is alio fometimes perpendicular to the fummit ; but very often it is oblique ; and in changing the fi- gure and extenfion bfthisj the animal alters its own whole Ihape at pleafure ; for the (mailer this bafe is, the more ele- vated is the top ; and, on the contrary, the broader it is, the flatter and lower is the whole fifh. The furface of the top of the cone is not flat, but convex, and has in its center aii aperture, which the creature makes larger or fmaller at plea- fure. In fome pofitions the whole fifli not unaptly refemblcs a purfe, only with this difference, that the body is not drawn up into any folds or wrinkles by the doling the aperture or mouth. In the middle of this purfe, as we call it, is placed the body of the fifh, touching this outer covering at the bottom on every fide, and of a conic figure, as that is. At its top, however, it is loofe, and ftands every way free from its co- vering ; the fides are more or lefs diftant from this free or loofe part of the body, as the aperture at the top of the cone is more or lefs open ; when it is nearly fhut up, very little of the body of the animal can be ken; but when it Opens it to different widths, mere or lefs of the body becomes vifible, and when it is at the wideft, every part of it, and all the horns, are feen perfecty diflinct. Thefe horns referable in ap- pearance thofe of the common fna'd ; but in their ufe they feem much more allied to the pipes or probofcides of the chamae kind, the fifh generally throwing out water at them on being touched. They are placed in three ranges on the internal furface of the covering, and are very numerous, their whole number not being lefs than 150.

The creature very often not only opens the outer covering or purfe to the utinoft width it is capable of, but at the fame time turns back its extremities ; in this cafe the internal part, or body of the fifh, becomes vifible on the furface, and at the fame time all the horns being, by this bending back of the fkin on which they grow, thrown into the pofture of fo many rays; the whole makes a very remarkable figure, and not unaptly refembles an anemony, or fome other fuch flowery when fully open. Very often alfo there is a great addition to the beauty of this appearance, by feveral round veficles of water, which appear blue, or of fome other lively colour. The general colour of the different fpecies of this fifh, or in- deed of the fame fpecies in different eircamftanees, is as va- variable as the fhape ; fometimes they are feen pellucid and colourlcfs, fometimes white, often yellowfli, fometimes of a rofe colour ; at other times they are of a beautiful green, and often of various (hades of brown. In fome thefe colours are equally diffufed through every part ; in others they are only feen in form of fpots and clouds or variegations ; fometimes thefe are irregularly difpofed, fometimes more regularly ; buc always with great beauty. The green ones have ufually a broad line of bl ue all round their bafe. The colours nor f hapes of thefe animals can be no marks of different fpecies; but the firmnefs of their flefh may ; in this they remarkably differ one from another, and this is a difference the more obvious, as their flefh is always open to the touch, there being no ihell, nor any other hard fubftance to cover it. However flow the progreffive motion of this fifh is, when examined it is found to depend on a very remarkable me- chanifm, to underftand which we muft attentively cortfider what is obvious to the eye in the ftructure of the creature, and remember the comparifon of the whole fiih to a purfe. We find that what refembles the bottom of that purfe is fiat, and is fixed to the rock, while the body of the fifh is

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