the oyster, in zoology, a genus belonging to the order of vermes testacea. The shell has two unequal valves; the cardo has no teeth, but a small hollowed one with transverse lateral breaks. There are 31 species, principally distinguished by peculiarities in their shells. The common oyster is reckoned an excellent food; and is eaten both raw and variously prepared. The character of the genus, in the words of Barbut, is, "The animal a tethys; the shell bivalve, unequivalve, with something like ears; the hinge void of teeth, with a deep oval hole, and transverse breaks on the sides. There is no womb nor anus." The genus is divided into four families, of which ostrea is the last. See PECTENS. The same author gives us the following enlarged account of the oyster.
"This sea-fish occupies in the scale of nature one of the degrees the most remote from perfection; destitute of defensive weapons and progressive motion, without art or industry, it is reduced to mere vegetation in perpetual imprisonment, though it every day opens regularly to enjoy the element necessary to its preservation. The animal figure, and the springs of its organization, are scarce discernible through the coarse and shapeless mass; a ligament placed at the summit of the shell serves as an arm to its operations. Oysters are reputed to be hermaphrodites; the spawn which they cast in May adheres to the rocks and other matters at the bottom of the sea; and in the space of 24 hours is provided with shells, in which are contained other oysters, that never leave the spot on which they were fixed, till the greedy fisherman tears them from the element. The green oysters eaten at Paris are commonly brought from Dieppe. Their colour is owing to the care taken to bed them in creeks, encompassed with verdure, whence they acquire their delicacy. Common oysters should be fresh, tender, and moist. The most esteemed are those caught at the mouth of rivers, and in clear water."
Great account is made of oysters from Brittany, but still greater of those that come from Marennes in Saintonge. Preference is given to those that are edged with small brown fringe, or beard, which epicures call fecundated oysters; but that those are females is a mistake. The want of fresh water renders oysters hard, bitter, and unpalatable. Mud and seaweeds destroy them in their very birth; galangal root, muscles, scollops, sea-stars, and crabs, are formidable enemies to the oyster. There are found in Spain red and russet coloured oysters; in Illyria, brown coloured, with the flesh black; and in the Red Sea, of the colour of the Iris. Oysters of the mangletree are of two sorts; those of St Domingo are delicate, adhering to the flumps of the trees that dip in the water. The negro divers cut them off with a bill, and they are served upon table with the roots."
Britain has been noted for oysters from the time of Juvenal, who, satyrizing Montanus an epicure, says,
Circe's nata forent, an Lucrinum ad saxum, Rutupinseae edita fundo, Ostrea, callebat primo deprenere morfu.
He, whether Circe's rock his oysters bore, Or Lucrine lake, or distant Richborough's shore, Knew at first taste.
The luxurious Romans were very fond of this fish, and had their layers or stews for oysters as we have at present. Sergius Orata was the first inventor, Pennant's as early as the time of L. Craufus the orator. He did Brit. Zool. not make them for the sake of indulging his appetite, p. 102. but thro' avarice, and made great profits from them. Orata got great credit for his Lucrine oysters; for, says Pliny, the British were not then known.
The ancients eat them raw, having them carried up unopened, and generally eating them at the beginning of the entertainment, but sometimes roasted. They had also a custom of stewing them with mallows and ducks, or with fish, and esteemed them very nourishing.
Britain still keeps its superiority in oysters over other countries. Most of our coasts produce them naturally; and in such places they are taken by dredging, and are become an article of commerce, both raw and pickled. The very shells, calcined, become a useful medicine as an absorbent. In common with other shells, they prove an excellent manure.
Stews or layers of oysters are formed in places which nature never allotted as habitations for them. Those near Colchester have been long famous; at present there are others that at least rival the former, near the mouth of the Thames. The oysters, or their spat, are brought to convenient places, where they improve in taste and size. It is an error to suppose, that the fine green observed in oysters taken from artificial beds, is owing to copperas; it being notorious how destructive the substance or the solution of it is to all fish. We cannot give a better account of the cause, or of the whole treatment of oysters, than what is preserved in the learned bishop Sprat's history of the Royal Society, from p. 307 to 309.
"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 a half-penny." penny. The spat cleaves to stones, old oyster-shells, pieces of wood, and such like things, at the bottom of the sea, which they call clutch. It is probably conjectured, that the spat in 24 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 forever. When they have taken them, with a knife they gently raise the small brood from the clutch, and then they throw the clutch in again, to preserve the ground for the future, unless they be so newly spat, that they cannot be safely severed from the clutch; in that case they are permitted to take the stone or shell, &c. that the spat is upon, one shell having many times 20 spats. After the month of May, it is felony to carry away the clutch, and punishable to take any other oysters, unless it be those of size, (that is to say) about the bigness of an half-crown piece, or when, the two shells being shut, a fair shilling will rattle between them.
"The places where these oysters are chiefly caught, are called the Pent-Burnham, Molden, and Colne-waters; the latter taking its name from the river of Colne, which passeth by Colchester, gives name to that town, and runs into a creek of the sea, at a place called the Hythe, being the suburbs of the town. This brood and other oysters they carry to the creeks of the sea, at Brickelsea, Melfy, Langno, Fingrego, Wivenho, Tollesbury, and Saltcoate, 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 salt-water until it is about a foot and 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. To prove that the sun operates in the greening, Tollesbury pits will green only in summer; but that the earth hath the greater power, Brickelsea pits green both winter and summer: and for a further proof, a pit within a foot of a greening-pit will not green; and those that did green very well, will in time lose their quality. 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 place, unless in cold weather, to cover themselves in the ose. The reason of the scarcity of oysters, and consequently of their dearth, 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 clutch, 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-fowl, because that fish gets into the oysters when they gape, and sucks them out.
"The reason that such a penalty is set upon any that shall destroy the clutch, is, because they find that if that be taken away, the ose will increase, and the mussels and cockles will breed there, and destroy the oysters, they having not whereon to stick their spat.
"The oysters are sick after they have spat; but in June and July they begin to mend, and in August they are perfectly well: the male oyster is black sick, having a black substance in the fin; the female white-sick (as they term it), having a milky substance in the fin. They are salt in the pits, salter in the layers, but fattest at sea."
The oyster affords the curious in microscopic observations a very pleasing entertainment. In the clear liquor many little round living animalcules have been found, whose bodies being conjoined, form spherical figures, with tails, not changing their place otherwise than by sinking to the bottom, as being heavier than the fluid; these have been seen frequently separating, and then coming together again. In other oysters, animalcules of the same kind were found, not conjoined, but swimming by one another, whence they seemed in a more perfect state, and were judged by Mr Leeuwenhoek to be the animalcules in the roe or semen of the oyster.
A female oyster being opened, incredible multitudes of small embryo oysters were seen, covered with little shells, perfectly transparent, and swimming along slowly in the liquor; and in another female, the young ones were found of a browner colour, and without any appearance of life or motion.
Monsieur Joblot also kept the water running from oysters three days, and it appeared full of young oysters swimming about nimbly in it; these increased in size daily; but a mixture of wine, or the vapour of vinegar, killed them.
In the month of August oysters are supposed to breed, because young ones are then found in them. Mr Leeuwenhoek, on the 4th of August, opened an oyster, and took out of it a prodigious number of minute oysters, all alive, and swimming nimbly about in the liquor, by means of certain exceeding small organs, extending a little way beyond their shells; and these he calls their beards. In these little oysters, he could discover the joinings of the shells; and perceived that there were some dead ones, with their shells gaping. These, tho' so extremely minute, are seen to be as like the large oysters in form as one egg is to another.
As to the size of them, he computes, that 120 of them in a row would extend an inch; and consequently, that a globular body, whose diameter is an inch, would, if they were also round, be equal to 1,728,000 of them. He reckons 3000 or 4000 are in one oyster, and found many of the embryo oysters among the bairds; some fastened thereto by slender filaments, and others lying loose: he likewise found animalcules in the liquor 500 times less than the embryo oysters.
It is not very uncommon to see on oyster-shells, when in a dark place, a shining matter or bluish light, like a flame of brimstone, which sticks to the fingers when touched, and continues shining and giving light for a considerable time, though without any sensible heat. This shining matter being examined with a microscope, was found to consist of three sorts of animalcules.