Natural History, Mollusca/Monomyaria
ORDER I. MONOMYARIA.
(Oysters and Scallops.)
On account of the beauty possessed by many members of this family, (a beauty comprising elegance of form, elaborate sculpture, and the most rich and brilliant colours,) their high development of organization, and, above all, the estimation in which they are held, and the extent to which they are consumed as human food, this must be considered as the most important of all the families of the Conchifera, or even of the Mollusca. Considerable variation, indeed, is found in the anatomy of these animals, and some of them entirely lack those organs which are found well developed in others; yet they possess so many characters in common, and glide into each other by gradations so close, that it is difficult to divide the group. All the tribe have the mantle widely open, no siphonal tubes, a single adductor muscle, and a ligament either entirely or in part concealed in the edge of the shell, lodged in a cardinal groove, and sometimes accompanied with teeth. In most cases there is a minute foot capable of spinning those threads which are called byssus, but this power is for the most part exercised only while the animal is young.
The Limes (Lima) and the Scallops (Pecten) are among the most active members of this Class of animals; they have been called the butterflies of the shell-fishes, a comparison not less apt on account of the delicacy and beautiful colouring of the wing-like shell, than of the agile motions which they exhibit. Though inhabitants of the deep sea, these bivalves take long and rapid leaps, shooting hither and thither, and fluttering about through the water with an irregular zig-zag movement, produced by the alternate opening and shutting of the valves with great force. The motions thus performed appear to be without any determinate direction, and to depend upon the impact of the valves upon the water; but these animals (the Pectens at least) have the power of effecting a more deliberate and precise locomotion, in the performance of which the mantle is the principal agent. The following observations, which I had recently an opportunity of making upon a young specimen of the Common Scallop or Quin (P. opercularis) which I was keeping in captivity, will serve to illustrate the form and office of the foot, as well as the faculty more immediately under consideration.
My attention was attracted to the Pecten by this curious circumstance, that it was adhering by one valve (the flat one) to the side of the glass phial, at some distance from the bottom. On close examination with a lens, I discovered that it was attached by a very delicate byssus. Curious to ascertain how it contrived to mount from the bottom to this position, I touched it slightly, and caused it to loose its hold. In the course of half an hour I found that it had resumed the same position again. I again disturbed it, and began to watch its motions. It was lying with the convex valve downwards on the bottom of the phial. The first thing I observed was the thrusting forth of the delicate little foot, an organ which seemed to me appropriately named, when I marked its close resemblance in form to a human foot and leg, enveloped in a white stocking. What I may call the sole of this tiny foot was pressed against the side of the glass, feeling about from place to place; while with the lens I could distinctly see, in the part corresponding to the toe, the opening of the fleshy lips, or sides of the grooves, in which the threads of byssus are said to be formed. While it was thus engaged my surprise was excited by seeing it suddenly throw itself with a jerk into an upright position; but the action was too startling to allow me to see how it was performed. I again laid it prone, and though for a moment it closed the valves, it presently opened them again, and performed a similar feat. This was followed by several leaps in different directions, in quick succession; but I was still at a loss to know the modus operandi. It appeared to me certain, that the ordinary supposition, viz. that the action is performed by the vigorous opening and shutting of the valves, was not the correct one. At length a favourable observation gave me a suspicion of the truth. I perceived the lips of the mantle (which were held in contact, though the valves were considerably separated) suddenly open to a partial extent, as if by blowing from within. At this instant there was a leap in the opposite direction, attended with a considerable agitation in the water. With this clue I observed more definitely. Having rendered the water a little turbid, in order the more distinctly to see any motion of the particles suspended in it, several leaps confirmed the notion that had suggested itself to me. The mode of proceeding is as follows: when the Pecten is about to leap, it draws in as much water as it can contain within the mantle, while the lips are held firmly in contact. At this instant the united edges of the lips are slightly drawn inward, and this action gives sure warning of the coming leap. The moment after this is observed, the animal, doubtless by muscular contraction, exerts a strong force upon the contained water, while it relaxes the forced contact of the lips at any point of the circumference, according to its pleasure. The result is, the forcible ejection of a jet of water from that point; which, by the resilience of its impact upon the surrounding fluid, throws the animal in the opposite direction, with a force proportioned to that of the jet d'eau. The action may be well imitated by the human mouth blowing a stream of air from any determined point, while the lips are held firmly together at all other points. The resemblance, indeed, of the mantle to the human lips performing such an action, (a resemblance perhaps more close than flattering,) struck me as ludicrously faithful. Nor was the appearance less suggestive of a pair of bellows without a nose, of which the valves were the covers, and the mantle the leathers, discharging their contents from any part of their sides.
The Oysters (Ostrea), on the other hand, are stationary; never moving from the spot where the egg is first deposited. Every one is aware that the shells are frequently found adhering in the firmest manner to rocks or stones, or to each other; the substance of the shell having been deposited upon the foreign body, so as to conform perfectly and minutely to every irregularity of its surface. "The shelly case of the Oyster," observes Sir Anthony Carlisle in his eloquent oration, "is its sole security, and a superior delicacy of touch, diffused over the whole of the living surfaces, warns the creature of every danger, and bids the closing of senseless valves. The inward organization is equally simple with the exterior forms, and both are suited to a passive life; for locomotive beings demand evidences of distant things,—sometimes to supply their wants, and on other occasions to inform them of danger; but a stationary creature, being doomed to rely on its fixed resources, would only be tantalised by evidences placed beyond its control."
In the Pectens, the edges of the mantle are furnished with eyes and tentacles; the Limes have the latter greatly developed, but the former organs are wanting, or very minute; the Oysters are destitute of both eyes and tentacles. The appearance of the eyes of the common Pecten has been already described (see p. 5). If we examine one of these organs under a microscope, say with a power of 220 diameters, we distinctly perceive it to be composed of a large globose lens, invested in a transparent coat, which is buried for more than half its volume in a socket of granular substance, and of a yellowish brown colour, having an ill-defined circle near its front part, of a blackish hue. This last, under continued pressure, bursts, and discharges a deep crimson pigment.The genera composing this family are very extensive, and widely spread; particularly in the seas of warm and temperate climates. In general
they are eaten wherever found, and are highly sapid and delicate. The common Scallop (P. opercularis) is said to have derived its local name of Quin from the partiality which the celebrated epicure of that name manifested for it; and the Great Scallop or Frill (P. maximus), a much rarer species, is sought after for the London markets. "Scalloped with bread crumbs in its own shell, or fried with a little vinegar and pepper, it forms a very delicious morsel; it has the sweet flavour which characterizes all the scallops. The deep valves of this shell are much used to contain scalloped oysters, and in fishermen's huts for rude but useful lamps."
The Oysters have a shell composed of two unequal valves, usually thick and irregular, connected by a hinge of the simplest character, without teeth. Externally the surface is rough, and composed of a great number of foliations loosely plaited, or marked with radiating furrows. The lower valve is more or less hollowed, the upper one flat.
The animal is shaped like the shell, having an open mantle with double edges, bordered by short fringes; the eyes, the tentacles, and the foot, are wanting.We have but one British species, the Oyster, par excellence (Ostrea edulis), but the abundance and renown of this species compensate for the absence of others. The British Oysters were held in the highest estimation by the ancient Romans, who were even at the expense of bringing them to Rome for their luxurious feasts. "Excellent as the oysters of Britain undoubtedly are, there are many degrees of that excellence, the animal varying much both in size and flavour, according to the nature of the coast, and the food with which the locality is furnished. The oysters on the south coast are generally very well flavoured;
ANIMAL OF THE OYSTER.
but it has been said that the best are found at Purfleet, and the worst at Liverpool. The Tenby oyster is large and rather coarse; but when fat is well-flavoured, and excellent when well stewed or pickled. Colchester, and other places in Essex, are the great nurseries or feeding-grounds for supplying the metropolis, and indeed, in a great measure, England generally, with this highly flavoured species. Here the Oysters collected at various places on the coast, even as far as Scotland, are brought, and laid on beds in creeks along the shore, where their flavour and size are rapidly improved. They have been known to augment the circumference of their shell even to the extent of an inch during the first two months, but in such cases the concavity within the valves is shallow."
Almost all the information we yet possess on the economy of the Oyster, is derived from Bishop Sprat's "History of the Royal Society," and is contained in a paper entitled, "The History of the Generation and Ordering of Green Oysters, commonly called Colchester Oysters." It reads as follows:—
"In the month of May the oysters cast their spawn (which the dredgers call their spat); it is like to a drop of candle, and about the bigness of an halfpenny. The spat cleaves to stones, old oyster-shells, pieces of wood, and such like things at the bottom of the sea, which they call cultch. It is probably conjectured that the spat in twenty-four hours begins to have a shell. In the month of May, the dredgers (by the law of the Admiralty Court) have liberty to catch all manner of oysters of what size soever. When they have taken them, with a knife they gently raise the small brood from the cultch, and then they throw the cultch in again, to preserve the ground for the future, unless they be so newly spat that they cannot be safely severed from the cultch; in that case they are permitted to take the stone or shell, &c. that the spat is upon, one shell having many times twenty spats. After the month of May it is felony to carry away the cultch, and punishable to take any other oysters, unless it be those of size (that is to say) about the bigness of a half-crown piece, or when, the two shells being shut, a fair shilling will rattle between them. The places where these oysters are chiefly catched are called the Pont-Burnham, Maiden, and Colnewaters. * * * This brood, and other oysters, they carry to creeks of the sea at Brickel-sea, Mersey, Langro, Fringrego, Wivenho, Folesbury, and Saltcoase, and there throw them into the channel, which they call their beds or layers, where they grow and fatten, and in two or three years the smallest brood will be oysters of the size aforesaid. Those oysters which they would have green, they put into pits about three feet deep in the salt-marshes, which are overflowed only at spring-tides, to which they have sluices, and let out the sea- water until it is about a foot and a half deep. These pits, from some quality in the soil co-operating with the heat of the sun, will become green, and communicate their colour to the oysters that are put into them in four or five days, though they commonly let them continue there six weeks or two months, in which time they will be of a dark green. . . .
"The oysters, when the tide comes in, lie with their hollow shell downwards; and when it goes out they turn on the other side. They remove not from their places unless in cold weather, to cover themselves in the ooze. The reason of the scarcity of oysters, and, consequently, of the dearness, is because they are of late years bought up by the Dutch. There are great penalties by the Admiralty Court laid upon those that fish out of those grounds which the court appoints, or that destroy the cultch, or that take any oysters that are not of size, or that do not tread under their feet, or throw upon the shore, a fish, which they call a five-finger, resembling a spur-rowel, because that fish gets into the oysters when they gape, and sucks them out.... The oysters are sick after they have their spat; but in June and July they begin to mend, and in August are perfectly well. The male oyster is black sick, having a black substance in the fin. They are salt in the pits, salter in the layers, saltest at sea."
For the most recent information respecting the oyster-beds which supply the London market, the extent of the supply, and the opinions of those practically concerned in their management and in the sale of their products, on points in the history and value of what may be termed cultivated oysters, we are indebted to Messrs. Forbes and Hanley, who obtained it from gentlemen of practical experience in the trade. From their valuable History of the British Mollusca the following particulars are extracted:—
"The oyster-beds from which the principal supply for the London market is procured, are those of Whitstable, Rochester, Milton, Colchester, Burnham, Faversham, and Queenborough, all artificial beds, furnishing natives. Since the introduction of steam-boats and railroads, considerable quantities of sea-oysters are brought from Falmouth and Helford, in Cornwall, from the coast of Wales, the Isle of Wight and its neighbourhood in Sussex, and even from Ireland and Scotland, after the winter sets in, as before they would not keep fresh enough when brought from long distances. The supply derived from natural beds varies much, since on some of them the oysters are not sufficiently abundant to pay for dredging. The sea-oyster is often, before being brought to market, kept for a time in artificial beds, in order to improve its flavour.
"The most esteemed oysters are those of the small ovate, but deep-shelled variety, called Natives, among which, those of the river Crouch, or Burnham Oysters, are pre-eminent for the marine flavour; probably on account of the facilities for rapid importation of them in fine condition. Much of the quality depends on the ground and condition of the beds: the oysters of different years from the same place often vary materially in this respect. They are considered full-grown for the market when from five to seven years old; sea-oysters at four years. The age is shown by the annual layers of growth, or 'shoots,' on the convex valve. Up to three or four years, each annual growth is easily observed, but after their maturity it is not so easy to count the layers. Aged oysters become very thick in the shell. In the neighbourhood of fresh water the oyster grows fast, and improves in body and flavour. The flavour is said by some to improve by shifting the oysters as they approach their full growth. Frost kills numbers, and when they are left dry at low ebbs, the run of fresh water from the land turns them, what is called, 'foxy,' of a brownish red colour. They are sometimes seized with sickness during the spawning season, and considerable numbers may die. Much labour is required to keep the beds in good order, cleansed from shells and rubbish, star-fishes, barnacles, corallines, and sea-weed, which grow freely in the spring of the year. On the cleanliness of the ground the prolific character of the bed, if the oysters breed there, depends. If carefully attended to, a bed may last any length of time; but if neglected, it will become overgrown with weed and buried in mud, so that it can only be reclaimed by restocking at a great expense, or is altogether destroyed. Artificial beds, for the purpose of keeping a supply at hand for the London market, are said to have been commenced about the year 1700, by the Kent and Essex Companies of Dredgers. The oyster does not breed freely, often not at all, on artificial beds, so that they require to be constantly restocked; and when they do spawn under such circumstances, the fry are said seldom to come to perfection. On their natural grounds they spawn profusely during the season, i.e. during the summer months."
The nature of the "spat" is thus explained by Sir Anthony Carlisle: "Oysters are viviparous, and the young are found within the tracheal passages, and between the folds of the coverlit (mantle), during the months of June and July in this climate. In its first state the oyster exhibits two semi-orbicular films, of transparent shell, which are continually opening and closing at regular intervals. The whole brood are associated together by being involved in a viscid slime, and in that state called the spat; it being common among viviparous animals of this kind to have their spawn deposited in contact with the lungs; the involving slime serves as the first nutriment, and we may infer, that the fœtal food so influenced by the gills is, at the same time, a respiratory supply to the imperfectly formed young."
"In London the chief consumption of common oysters is from the 4th of August to January, and of natives from October to March. The consumption is said to be greatest during the hottest months after the commencement of the oyster season; the warmer the weather, the more oysters are consumed. They are brought to market in craft of various sizes; they are packed in bulk closely in the hold; in some cases a cask of saltwater is kept, from which to sprinkle them superficially. Those that come by rail are packed with the convex shells downwards, in bags or barrels. From the boats they are transferred to the salesmen, who keep them in a little salt and spring water, and shift them every twelve hours. Some pretend to improve them by 'feeding' them on oatmeal. Oysters, like other bivalves, live chiefly on infusoria. The quantity consumed annually in London varies in different seasons. One informant states twenty thousand bushels of natives, one hundred thousand bushels of common oysters, to be about the mark: another estimates the quantity sold in the season, from the 4th of August to the 12th of May, to be nearly one hundred thousand London bushels; each bushel being three Manchester, or imperial, bushels; and that about thirty thousand bushels of natives are sold during the same period by various Companies. During the season, commencing on August the 4th, 1848, and ending May 12th, 1849, Mr. Wickenden estimates about one hundred and thirty thousand bushels of oysters to have been sold in London, though of that quantity about one fourth was sent away to various parts of the United Kingdom and the Continent." 
The members of this family effect a transition from those genera which have but a single muscle, to those which have two; for though their shells display two, or even more muscular impressions, one is always found to predominate greatly over the rest, which are but small.
The shell has its exterior portion commonly black, or of the colour of horn, and composed of prismatic cellular substance; the interior layers are composed of nacre, and are therefore brilliantly pearly. Their form is very irregular, the valves being unequal, and always developed more towards one side than the other. The hinge is without teeth, the ligament thin, simple, or notched.
The animals have a mantle which does not adhere to the shell, entirely open all round, prolonged into irregular lobes, without siphons; there is a small foot which is grooved, and capable of spinning a strong byssus.
The most important genus of the family contains the Wing-shells, one species of which is the Pearl-oyster, from the interior shell of which we obtain the substance known as mother-of-pearl, which is largely imported into this country, and manufactured into shirt-buttons, knife-handles, and various trinkets; it is also much used for ornamental inlaying. But that which renders this shell of much more value is the production of pearls, the beauty of which has always rendered them fit companions of the choicest precious stones, for the purpose of personal adornment.
Pearls are indeed produced by several genera of shells both bivalve and univalve, but the most precious are obtained from the species named Avicula margaritifera, which is a native of the Indian Ocean. On the coast of India and Persia numerous fisheries are established, which supply the markets of the world with precious pearls. Some of these have been carried on from very ancient times; that for example at Catifa in Arabia, which produced the celebrated pearl bought by Tavernier for 110,000l., is mentioned by Pliny.
The most productive fisheries are prosecuted in the Persian Gulf, and on the coast of Ceylon; that of the Bahrein Islands, in the former locality, often produces pearls to the value of 90,000.l sterling in two months, the time in which it is prosecuted. This is free to all adventurers on payment of the tax, but the fishery of Ceylon is a monopoly in the hands of government.
"There is perhaps no spectacle," says the author, "which the island of Ceylon affords more striking to a European than the Bay of Condatchy during the season of the pearl fishery. This desert and barren spot is at that time converted into a scene which exceeds, in novelty and variety, almost anything I ever witnessed: several thousands of people of different colours, countries, castes and occupations continually passing and repassing in a busy crowd; the vast numbers of small tents and huts erected on the shore, with the bazaar or market-place before each; the multitude of boats returning in the afternoon from the pearl banks, some of them laden with riches; the anxious expecting countenances of the boat owners, while the boats are approaching the shore, and the eagerness and avidity with which they run to them when arrived, in hopes of a rich cargo; the vast numbers of jewellers, brokers, merchants of all colours and all descriptions, both natives and foreigners, who are occupied in some way or other with the pearls, some separating and assorting them, others weighing and ascertaining their number and value, while others are hawking them about or drilling and boring them for future use,—all these circumstances tend to impress the mind with the value and importance of that object which can of itself create this scene.
"The Bay of Condatchy is the most central rendezvous for the boats employed in the fishery. The banks, where it is carried on, extend several miles along the coast from Manaar southward off Arippo, Condatchy and Pomparipoo. The principal bank is opposite to Condatchy, and lies out at sea about twenty miles. After the survey of the state of the beds, and the consequent report to Government, the particular banks to be fished are put up for sale to the highest bidder, and are usually purchased by a black merchant. The Government, however, sometimes judges it more advantageous to fish the banks on its own account, and to dispose of the pearls to the merchants.
"The banks are divided into three or four different portions, which are fished annually in succession. These portions are distinct, and are set up separately to sale, each in the year in which it is to be fished. A sufficient interval is thus given to the oysters to attain their proper growth; and as the portion first used has generally recovered its maturity by the time the last portion has been fished, the fishery becomes almost regularly annual, and may thus be considered as yielding a yearly revenue. The oysters are supposed to attain their complete state of maturity in seven years.
"The fishing season commences in February, and ends about the beginning of April. The period allowed to the merchant to fish the banks is six weeks, or two months at the utmost; but there are several interruptions which prevent the fishing days from exceeding more than about thirty. If it happen to be a very bad season, and many stormy days intervene during the period allotted, the purchaser of the fishery is often allowed a few days more. …
"A signal gun is fired at Arippo about ten o'clock at night, when the whole fleet sets sail with the land-breeze. They reach the banks before daybreak, and at sunrise commence fishing. In this they continue busily occupied till the seabreeze, which arises about noon, warns them to return to the bay. As soon as they appear within sight, another gun is fired, and the colours hoisted, to inform the anxious owners of their return. When the boats come to land, their cargoes are immediately taken out, as it is necessary to have them completely unloaded before night. Whatever may have been the success of their boats, the owners seldom wear the looks of disappointment; for although they may have been unsuccessful one day, they look with assurance of better fortune to the next; as the Brahmins and conjurors, whom they implicitly trust, in defiance of all experience, understand too well the liberality of a man in hopes of good fortune, not to promise them all they can desire.
"Each of the boats carries twenty men, with a tindal, or chief boatman, who acts as pilot. Ten of the men row and assist the divers in re-ascending. The other ten are divers; they go down into the sea by five at a time; when the first five come up, the other five go down, and by this method of alternately diving, they give each other time to recruit themselves for a fresh plunge.
"In order to accelerate the descent of the divers, large stones are employed: five of these are brought in each boat for the purpose; they are of a reddish granite, common in this country, and of a pyramidal shape, round at the top and bottom, with a hole perforated through the smaller end sufficient to admit a rope. Some of the divers use a stone shaped like a half-moon, which they fasten round the belly when they mean to descend, and thus keep their feet free.
"These people are accustomed to dive from their very infancy, and fearlessly descend to the bottom in from four to ten fathoms water in search of the oysters. The diver, when he is about to plunge, seizes the rope to which one of the stones we have described is attached, with the toes of his right foot, while he takes hold of a bag of network with those of his left, it being customary among all the Indians to use their toes in working or holding as well as their fingers; as, such is the power of habit, they can pick up even the smallest thing from the ground with their toes almost as nimbly as a European could with his fingers. The diver, thus prepared, seizes another rope with his right hand, and holding his nostrils shut with the left, plunges into the water, and by the assistance of the stone speedily reaches the bottom. He then hangs the net round his neck, and, with much dexterity and all possible despatch, collects as many oysters as he can while he is able to remain under water, which is usually about two minutes; he then resumes his former position, makes a signal to those above by pulling a rope in his right hand, and is immediately by this means drawn up and brought into the boat, leaving the stone to be pulled up afterwards by a rope attached to it."
The serious effects which so protracted a submersion must produce upon the human frame, are manifested by a discharge of water from their mouths, ears, and nostrils, and frequently of blood. But this does not hinder them from going down in their turn. "They will often," continues our author, "make from forty to fifty plunges in one day, and at each plunge bring up about a hundred oysters. Some rub their bodies over with oil, and stuff their ears and noses to prevent the water from entering, while others use no precautions whatever. Although the usual time of remaining under water does not much exceed two minutes, yet there are instances known of divers who could remain four or five minutes, which was the case with a Caffre boy the last year I visited the fishery. The longest ever known was that of a diver who came from Anjango in 1797, and who absolutely remained under water full six minutes."
The last named period seems almost incredible, but there is no reason to doubt Captain Percival's evidence. The chief horror and danger awaiting the diver are concentrated in the ground-shark. This animal is a common and fearful inhabitant of all the seas in these latitudes; and its terrors are so continually before the eyes of the divers, that they seek a vague safety in supernatural means. Before they begin diving, the priests or conjurors, who are known in the Malabar language by the name of Filial Karras, or binders of sharks, are always consulted, and whatever the conjuror says to them is received with the most implicit confidence.
The divers are paid differently, according to their private agreement with the boat-owners, either in money, or with a proportion of the oysters caught, which they take the chance of opening on their own account; the latter is the method most commonly adopted. The agreements with the people who hire out the boats are conducted much in the same manner. They contract either to receive a certain sum, or permission to fish on their own account. Some of those who pursue the latter plan are very successful, and become rich, while others are great losers hy the speculation. The spirit of gambling is more openly exhibited, for oyster lotteries are carried on to a great extent, and they consist of purchasing a quantity of the oysters unopened, and running the chance of either finding or not finding pearls in them. These lotteries are great favourites with European officers and gentlemen. The boat-owners and the merchants lose some of the best pearls while the boats are on their return to the bay from the banks, as the oysters when alive, and left for a time undisturbed, frequently open their shells of their own accord; a pearl may then be easily discovered, and the oyster prevented, by means of a bit of grass, or soft wood, from again closing its shell, till an opportunity offers of picking out the pearl.
Captain Percival thus concludes his interesting account:—"As soon as the oysters are taken out of the boats, they are carried by the different people to whom they belong, and placed in holes or pits, dug in the ground to the depth of about two feet, or in small square places, cleared and fenced round for the purpose, each person having his own separate division. Mats are spread below them to prevent the oysters from touching the earth, and here they are left to die and rot. As soon as they have passed through a state of putre-faction, and have become dry, they are easily opened, without any danger of injuring the pearls, which might not be the case if they were opened fresh, as at that time to do so requires great force. On the shell being opened the oyster is minutely examined for the pearls; it is usual even to boil the oyster, as the pearl, though commonly found in the shell, is not unfrequently contained in the body of the fish itself.
"The stench occasioned by the oysters being left to putrefy is intolerable, and remains for a long while after the fishing is over. It corrupts the atmosphere for several miles round Condatchy, and renders the neighbourhood of that country extremely unpleasant till the monsoons and violent south-west winds set in and purify the air. The nauseous smell, however, is not able to overcome the hope of gain; for months after the fishing season, numbers of people are to be seen earnestly searching and poring over the sands and places where the oysters had been laid to putrefy; and some are now and then fortunate enough to find a pearl that amply compensates their trouble in searching after them. In 1797, while Mr. Andrews was collector, a coolie, or common fellow of the lowest class, got by accident the most valuable pearl seen that season, and sold it to Mr. Andrews for a large sum.
"The pearls found at this fishery are of a whiter colour than those got in the Gulf of Ormus, on the Arabian coast, but in other respects are not accounted so pure, or of so excellent a quality; for though the white pearls are more esteemed in Europe, the natives prefer those of a yellowish or golden cast. Off Tutucoreen, which is on the Coromandel coast, nearly opposite to Condatchy, there is another fishery; but the pearls found there are much inferior to those two species I have mentioned, being tinted with a blue or greyish tinge.
"In preparing the pearls, particularly in drilling and stringing them, the black people are wonderfully expert. I was very much struck with the instrument they employ in drilling, as well as the dexterity with which they use it. A machine made of wood, of a shape resembling an obtuse inverted cone, about six inches in length and four in breadth, is supported upon three feet, each twelve inches long. In the upper flat surface of this machine holes or pits are formed to receive the larger pearls, the smaller ones being beat in with a wooden hammer. The drilling instruments are spindles of various sizes, according to that of the pearls; they are turned round in a wooden head by means of a bow-handle to which they are attached. The pearls being placed in the pits which we have already mentioned, and the point of the spindle adjusted to them, the workman presses on the wooden head of the machine with his left hand, while his right is employed in turning round the bow-handle. During the process of drilling he occasionally moistens the pearl, by dipping the little finger of his right hand in a cocoa-nut filled with water, which is placed by him for that purpose; this he does with a dexterity and quickness which scarcely impede the operation, and can only be acquired by much practice.
"They have also a variety of other instruments both for cutting and drilling the pearls. To clean, round, and polish them to that state in which we see them, a powder made of the pearls themselves is employed. These different operations in preparing the pearls, occupy a great number of the black men in various parts of the island. In the black town or pettah of Columbo, in particular, many of them may every day be seen at this work."
The largest British bivalves belong to the genus Pinna, in which the shell is fibrous, and horny in texture, rather fragile and delicate; the valves are equal, triangular and exceedingly one-sided; the hinge is straight, long and toothless, the ligament marginal, and almost wholly internal.
The animal is triangular, with the mantle freely open and having fringed edges; the foot is small, conical, or tongue-like, and grooved; there is a small anterior muscle in the angle; the posterior one is by far the larger.
The genus contains but few species, which are, however, widely distributed, and most of them are of large size; they range from deep water to near the shore, living on sandy or muddy bottoms, with their beaks plunged deep into the ground, and the broad extremity gaping upwards.
In a cabinet of British shells the eye is sure to be attracted by the great fan-like horny valves of the Pinna (Pinna pectinata), which are not uncommonly seen twelve inches long, and seven broad at the gaping end. Young specimens are of a semi-transparent horny texture, partially covered with rows of hooked spinous scales; but these spines are almost always worn away in old examples. The interior is pearly in a slight degree, and loose pearls of dull colour are sometimes found within the shells. The silky byssus spun by these mollusks, which is capable of being woven into small articles of wearing apparel, has been already noticed.
The great Pinna is found all around the British coast, chiefly in deep water. Montagu found a bed of them in Salcomb Bay, which was occasionally accessible when the tide receded beyond its usual limits. The valves stood upright, with the broader end about an inch above the surface, and the lower end fixed so firmly to the soil by a very large strong byssus two or three inches in length, composed of numerous fine silky fibres of a dark purplish brown hue, as to demand the exercise of considerable force for their removal.
Mr.Couch, in his "Fauna of Cornwall," observes that "this species is found in the greatest abundance at the distance of from three to six leagues south of the Deadman Point, where they stud the bottom in multitudes, with only two or three inches of the pointed end inserted into the soil. It is common for the line or hook to become entangled among these shells, and powerful effort is required to drag them from their attachment, which is only effected by breaking the byssus, or tearing away the ground to which it is attached. In the latter case a rich harvest of shells is often afforded, but the pointed end of the Pinna is usually broken off by the violence. It is perhaps owing to the different degree of solidity of the ground, that the shells living in the deeper water are so much less buried than those of which Montagu speaks, and one of the consequences may be a greater degree of motion in the shell. Montagu observes that the exposed end cannot be closed by art, but the animal is capable of effecting it; and observation has taught me, that this is its method of obtaining food. In its ordinary position this opening is about two inches wide, exposing the contained animal, which occupies but a small portion of the cavity, and seems to offer itself a prey to the first creature that may choose to devour it. Some fish is thus tempted to enter, but the first touch within is a signal for its destruction. The shell closes not only at the side but at the top, the latter action being effected by a separation of the pointed ends, and the captive is either crushed to death, or soon perishes from confinement."
- Hunterian Oration, 1826.
- Forbes and Hanley, ii. 298.
- Juvenal, Sat. iv. 140.
- Penny Cyclop. xvii. 363.
- Rather from the abundant increase in such pits of the green Infusoria and Desmideœ, on which the Oyster feeds.
- Hunterian Oration, 1826.
- Forbes and Hanley, ii. 315.