Page:Cyclopaedia, Chambers - Supplement, Volume 2.djvu/235

 PHO

PHOLAS, in natiiral hiftory, the rianie of a genus of {hells, the characters of which are thefe : It is an oblong multiValve fhell, compofed of five fhells, tho* in fome, improperly ac- counted fpecies of this genus, only of two. It is fmooth in fomefpecies, in others rough, and in fome reticulated; in fome fpecies it fhuts clofe and even, in others it gapes always open. Of the oblong fhells, ufually called pholades, and confift ing only of two fhells, we meet with the following fpecies : 1. The fmooth pbolas, of Rondeietius. i. The fmooth nar rower pbolas, of Aldrovand. 3. The wood-pbolas, of Rum- phius. 4. The fmooth mufcIe-Jikc pbolas. 5. The finger- fholas,of Bonani. 6. The pale red and white pbolas. Of the oblong and irregular pho'ades, which confift only of two valves, we have the following fpecies: 1. The great American pbolas. 2. The broad pbolas, with the long trunk. Of the oblong irregular pbolas, confifting of five valves, we have only one known fpecies, which is the pbolas of Lifter. See Tab. of Shells, N°. 29. and Hift. Nat. Eclairc. p. 356. The word pbolas is derived from the Greek, and fignifies no more than any thing which is hidden ; the name was given to this genus of fhell-fifh from their cuftom of making themfelves holes in earth, fend, ftones, or wood, and living hidden in them. Many being of opinion, that thefe fifh could not work themfelves into the fubftance of hard ftones, have thought that they were hatched in holes accidentally formed in ftones, and that the fhells naturaly grew of fuch a fhape as was neceflary to fill the cavity. Nor is this the only error propagated concerning the pbolas ; for as all that was fignified by the name being only that the fhell was hidden in fome folid fubftance, whenever an author found a ihell-fifh of what- ever kind thus buried in (lone, he defcribed it under the name of pbolas.

There are many fpecies cf the fhell-fifh, and thefe of feveral different genera, which thus hide themfelves in ftone ; and thefe have therefore been called by different authors pholades ; and hence it has been faid, that the pbolas was in fome fpecies a bivalve, and in others a muitivalve fliell. The true pboIas 3 which Lifter has very well defcribed, is a genuine muitivalve. being compofed of live pieces ; but this is a very fcarce fifh, and feveral of the mufcles and of the chamae being often found in ftone, they have all been called bivalve pholades ; and fuch as have found the chamse thus immerfed, and found them really to confift of only two fhells, have cenfured the authors of error who have defcribed the pbolas as having five. Hift. Nat. Eclairc. p. 362.

All the fpecies of fhell-fifh which are found in ftone, have certainly been the means of making the holes in which they are found: the facTt is inconteftible, but the means yet wholly unknown. Perhaps when fome accurate obferver fliall have an opportunity of examining the fifh alive, the myftery will be cleared up. All that we know at prefent is, that they are firft buried in the ftone while very fmall ; fince the aperture on the furface of the ftone is ufually much fmaller than the diameter of the fliell contained within, and only ferves to admit the fea water, or to give paflage to the probofcis of the inclofed fifh.

The chamae, which are frequently known among us under thi name of die pbolas, and common about our fhores, are often found in a foft ftone of the feptaria or ludus Hehnontii kind _ an4 as there is a great refemblance between this ftone and a hardened clay in its external appearance, many have fallen into an opinion of its being a petrified clay. On this prin ciple it has feemed eafy to account for the ftrange phsno^ menon of the fho'ades or chamae being found in it, fince it has been fuppofed that they made their way into it while in the ftate of clay, and that it afterwards became petrified or hardened into ftone while they were in it. But not to men tion the error of the opinion of this fort of ftone being ; petrified clay, or the abfurdity of fuppofing that fuch a pe- trifaction, were it made at all, could be effected in fo (hort a time as during the life of the fifh. It is eafy to anfwi this opinion by another obfervation, which is, that on the coafts of Italy it is not uncommon to find wrought pieces of hard marble, formed into pillars and other ornamental parts of building, in which are lodged the true pholades, as alfo cha- nge and mufcles, in the fame manner as in our fofter ftones. It is not to be fuppofed that thefe pieces of marble were ever any thing elfe but marble; and we have an account from Woodward of certain columns of marble which were dragged up out of the fea, after their having been loft there but a few years before, and thefe were all full of pholades. If any thing could he wanting after this to prove the certainty of the fa£r, that the pholades make themfelves the holes they live in, it might be added that they are often found lodged in wood, as well as in different kinds of ftones; the bottoms of fhips being frequently pierced by them. There is an opinion among the vulgar, that the pholades, after a time, change into butterflies; hut this is too abfurd to need a re- futation. 7 he fifh is very good to eat, and is taken in quan- tities on breaking the ftones; for they never live fingly, but many in the fame ftone.

In the memoirs of the academy of fciences it is faid, that the fliell of the pbolas is compofed of three pieces, two of Svi'ri.. Vol.. II.

PHO

which are equal in fee and alike in fhape ; and the third* which ,s vartly fmaller than thefe, is placed near the funrmit of the others, and fills up a little fpace, which they leave empty: this is ufually of the figure of a lozenge, one of the (harp ends of it coming in contact with the other fhells at their tops ; but fometimes it is only pointed at both ends and rounded in its intermediate patt, and the external furface ot it is ufually convex. The two large valves of the (hell are twice or three times as long as they are wide, and the cardo, which joins them, is placed near one end; they grow gradually fmaller to the other extremity, where they termi- nate in an oval. They are furrowed and channelled in the manner of a file, having many longitudinal Breaks eroded by a great number of tranfveife ones ; thefe lines mark the age or different growths of the fifh, and their ridges are of- ten befit with fmall points like prickles. The two valves of the fhell are ufually open, and are capable of expanding to a great width ; but they do not expofe, or leave naked the body of the fifh on this occafion ; for they are connected to- gether by a membrane which opens to give them room, and forms with the two fhells a fort of cafe for the body of the fifll ; and indeed this was the more neceflary, as the figure of the fhells is fuch, that they cannot ever perfcaiy clofe to- gether, for when they come into contafl in one part, another neceflarily remains open from their fhape. Mem. Acad. Par. 1712.

The holes in which the pholades lodge are ufually twice as deep, at lead, as the fliell is long; and the figure of thefe holes is, that of a truncated cone, except that they are ter- minated at the bottom by a hollow rounded cavity, and their pofition is ufually fomewhat oblique to the horizon. The openings of thefe holes are what betray the philafs being in the ftone ; hut they are always very fmall, in proportion to the fize of the fifh. There feems to be no progrefTive mo- tion of any animal in nature fo (low as that of the fhclns ; it is immerfed in the hole, and has no movement except a fmall one toward the center of the earth; and this is only proportioned to the growth of the animal. Its work is very difficult in its motion, but it has great time to perform it in, as it only moves downward, (inking itfelf deeper in the ftone as it increafes itfelf in bulk. The part by means of which it performs this, is a fle(hy fubftance placed near the lower extremity of the (hell ; it is of the fhape of a lozenge, and is confiderably large in proportion to the fize of the animal ; and tho' it be of a foft fubftance, it is not to be wondered at that in fo long a time it is able, by coilftant work, to bur- row into a hard ftone. The manner of their performing this may be feen by taking one of them out of the ftone° and placing it upon fome foft clay ; for they will immediately get to work in bending and extending that part allotted to dig for them, and in a few hours they will bury themfelves in the mud in as large a hole as they had taken many years to make in the ftone. They find little refiftance in fo foft a fubftance, and the neccflity of their hiding themfelves evidently makes them haften their work. The animal is lodged in the lower half of the hole in the ftone, and the upper half is filled up by a pipe of a fleflly fubftance and conic figure, truncated at the end : this they ufually extend to the orifice of the hole, and place on a level with the furface of the ftone ; but they feldom extend it any farther than this. The pipe, tho' it appears Angle, is in reality compofed of two pipes, or at leaft it is compofed of two parts feparaled by a membrane. The ufe of this pipe or probofcis, is the fame with that of the probofcides of other fhell-fifh, to take in fea water into their bodies, and afterwards to throw it out again. In the middle of their bodies they have a fmall green veflel, the ufe of which has not yet been difcovereel ; this, when plunged in fpirit of wine, becomes of a purple colour ; but its colour on linnen will not become purple in the fun like that of the murex ; and even if it would, its quantity is too fmall to make it worth preferving. Mem. Acad. Par. 17 12.

The true or muitivalve pbolas is compofed cf two large fhells, two other fmall ones at the back, and one long narrow and crooked one at the cardo. The three fmall fheiis always fall off as foon as the creature is dead ; hence we ufually fee the true pho /as, with only two (hells, in cabinets, and hence fome have called it a bivalve, and others a trivalve Ihell, having found one of the three other valves. Some alfo rretend, that the Englifh pholades befide the five pieces already mentioned, have another, which ferves as an operculum. Many are of opinion, that the pholades bore their way into the ftones, by means of their rough (hells, but Bonani is of opinion, that they do it with certain teeth. Lifer's Hift of Animal. Engl. p. 172. J/dnvand de Teftac. 1 3. Binani Recreat. Ment. et Oculi. p. 16. PHO LIS, in natural biftory, the name of a genus of foffils of the clafs of the gypfums or plaifter ftones,' the tliftinguifhing characters of which are, that the bodies of it are confider- ably hard, compofed of fomewhat broad particles, and of a bright cryftalline luftre.

The word is derived from the Greek pixV, a fcale,or fmall Sake, from thefe bodies being compofed of particles of that form.

2 I i The