Oysters are delicate morsels—still appreciated by that class of the population which nevertheless shudders at the thought of eating the high-flavoured “whilk” or the gristly “periwinkle,” and neglects the admirable mussel, so rightly valued by our French friends. There are a number of interesting facts about the nature and life-history of oysters, and the different kinds of them—a knowledge of which does not diminish, but, on the contrary, rather adds to the pleasure with which one swallows the shell-fish. I remember the time when “natives” were sold in London at sixpence the score. When I was a schoolboy at St. Paul’s they were no more than sixpence a dozen at the best shops in Cheapside. That inevitable form of British enterprise which is known as “monopoly,” many years since laid hold of the oyster business, and rapidly raised the price of the best natives to eight times what it had been, while the typhoid “scare” came subsequently as a sort of poetical justice, and threatened to ruin the oyster monopolists. As a matter of fact, there is no difficulty in freeing oysters from any possible contamination by the typhoid germ. They have only to be kept for ten days or a fortnight in large tanks of sea-water of unquestionable purity—after removal from the fattening grounds (tanks or waterways), and they rid themselves of any possible infection. It is the interest of the oyster merchant to make sure that this treatment is strictly enforced. It is a noteworthy fact that the anciently established habit of drenching an oyster with vinegar before eating it is precisely the best treatment, except cooking them, which could have been adopted in order to destroy the vitality of typhoid germs—although the existence of such germs was unknown when the practice arose, and vinegar or lemon-juice was taken with uncooked oysters as a matter of taste, not as a safeguard.

The oyster is sometimes grandiloquently styled “the succulent mollusc”—and it is classed together with other bivalve shells and true “shell-bearing” shell-fish, such as whelks and snails (not lobsters and crabs, which are Crustacea), in a great division of animals known to naturalists as the Mollusca. This word is only a Latin form of the name Malakia, which was given to the cuttle-fishes by that wonderful man Aristotle, the Greek—and means “soft creatures.” A bivalve, or two-shelled mollusc, like the oyster, may be compared to an oblong notebook. The hard covers correspond to the two shells and the back to a horny piece by which the two shells are united, forming the hinge. If you place a piece of indiarubber (a thickish bit) between the covers of the notebook so that it lies near the back, and then try to shut the book, you find that it requires some pressure to do so; when you leave off pressing them the covers gape. The horny hinge-piece or ligament of the shells of the oyster and other bivalves acts in this way. The shells are only kept closed by a strong muscle, which runs across from shell to shell (Figs. 28 and 30m). When the oyster is at rest or when it is dead the muscle does not act, and the elastic hinge-piece or ligament causes the shells to gape. The animal within the shells may be compared to the leaves of the notebook. Suppose there are twenty-six leaves, then the outermost leaf on each side corresponds to the two soft living membraneous flaps which secrete the two shells or covers of the oyster and lie closely on them (a, b, Figs. 28 and 30); the next two on each side (rather shortened leaves, folded in from below) are the flat gills or “gill-plates” of the mollusc (g¹ to g⁴ in Fig. 28); whilst we must suppose the twenty middle leaves to be “pulped” and fused together to represent the body of the shell-fish.

The oyster’s gill-plates, commonly called “the beard,” are covered on the surface by microscopic hairs of a very remarkable kind (Fig. 29). They are soft, living protoplasm, and are continually “lashing,” bending forwards and straightening again at the rate of some three or four hundred strokes to the minute. They all work rhythmically together, and produce a strong current in the water, which bathes the surface of the oyster when the shells are open. Such microscopic vibrating hairs are very common in aquatic animals, and are called “cilia.” The current which they produce causes oxygen-holding water to flow from without over the gills, and so aerate the blood of the oyster, and also carries into the chamber protected by the shells excessively minute particles, chiefly microscopic plants, which are driven on to the small, open mouth of the oyster, placed far up on its body. These microscopic food-particles are wafted down the oyster’s throat by similar vibrating hairs into the stomach and intestine. An oyster has no other means of taking food, and almost without cessation, as the oyster lies on the sea bottom with its muscle relaxed and its shell “gaping,” the nourishing stream is kept going. If poisonous matter, bad water, or some violent disturbance make themselves apparent, the shell-muscle acts, and the oyster tightly closes his shell. Such things make themselves “apparent” to the oyster, for it has a nervous system, and though it has no eyes (the nearly allied “scallop” has a number of eyes) it has a delicate sense of smell and touch, and also what is usually considered to be an organ of hearing.

The oyster has also a heart and blood-vessels (Fig. 30) and blood; in some few bivalves and snails the blood is red like our own. The beating of the heart may be seen by careful examination of a freshly opened specimen. The oyster has also a “liver,” or digestive gland, and a kidney and a soft, branched, tubular structure embedded in the body, within which the egg-cells and sperm-cells grow by means of which the oyster propagates itself in the summer. Our north European oyster produces in the same individual both egg-cells, and the male fertilising sperm-cells or spermatozoa. The eggs are just visible to the unaided eye (Fig. 31), and as many as a million are produced in the warm breeding season by a single ripe oyster. About a fortnight after the eggs have been shed, the same tubular chambers in the oyster’s body which produced the eggs by growth from their inner walls, produce the spermatozoa, so that they are too late to fertilise the eggs of the same oyster. They pass out of the oyster into the sea water, and are carried within the shelter of the shells, and so on to the surface of the protected bodies of other neighbouring oysters by the currents created by the “ciliated” gill-plates of these neighbours.

The sperm particles or spermatozoa (Fig. 32) are produced by millions, and form a cloud finer than dust in the sea water. They are carried within the shells of both egg-producing and sperm-producing oysters, and are driven along into the openings of the tubular reproductive sacs, and into those sacs in the case of those oysters which are at the time producing eggs. There they fertilise the eggs. The minute eggs begin to develop whilst still within the parent’s body, and continue to do so whilst remaining within the shelter of the shell, adhering to the gill-plates (Fig. 33). In a day or two each fertilised egg has developed into a very minute creature, provided with a tiny circlet of cilia or vibratile hairs, the movements of which cause it to swim (Fig. 33F). The parent oyster is now said to be “white-sick.” In the course of a couple of days the young oyster still within its parent’s shell becomes dark in colour, and has formed on its surface a pair of symmetrical shells, not like those of an adult oyster, but convex (Fig. 34) like those of a clam or a cockle. The head region, with its circlet of vibrating cilia, can be projected between the open shells or withdrawn between them when the shells are shut. The mother oyster, laden with these little dark specks, is now said to be “black-sick.”

In the course of a week or so the brood of dark young oysters escapes by thousands from the parent’s shell into the surrounding water. They swim by their circlet of vibrating hairs, or “velum,” as it is called, towards the surface, and are carried far and wide by the tides. They are active, transparent little “dots,” very unlike their parent (Fig. 34). The next thing that happens to them—after a few days, perhaps weeks—is that owing to the increasing weight of their shells, they sink to the bottom. More than half perish by dropping thus on to bad ground; a vast number have already been eaten by young fishes and shrimps. Those which are lucky enough to fall on to something hard—stones, rocks, old oyster-shells, or the shells of living oysters—become cemented to those hard substances by the new shelly substance formed by the growing edge of the lowermost of their little shells, which now spread out, lose their cockle-like shape as they grow, and become, the one (the left by which it is fixed) large, deep, and bossed, the other flat. The little oysters are only one-fortieth of an inch in diameter when first they become fixed, but they grow rapidly, feeding in the same way as their parents. Vast numbers are eaten by other animals. In some localities in two years, in others in three years, they have grown to a couple of inches in length, and now produce in the summer breeding season a certain quantity of eggs and sperm to start new generations. The oyster continues to grow, and at five to seven years of age is in full vigour and maturity; at ten years of age it produces few eggs, or sperm-cells; and in the course of another year or so, under natural conditions, dies.

Enormous as is the output of young by a single oyster—amounting to something like a million a year in probably four or five successive years—yet it must be remembered that on the whole, taking all the various oyster-beds into account, some of which increase whilst others dwindle or actually die out altogether, there is no increase in the oyster population of the seas. Taking them all round, five million young oysters start life in order that one may finally come to maturity, so many and varied and incessant are the dangers, the predatory enemies, the destructive effects of cold currents, bad ground, and other chances of life and death on to which the swarming swimming young are launched.

The above brief history applies to the North Sea or Channel oyster, which is also found (with other species) in the Mediterranean. The American and the Portuguese oyster differ from it in being of distinct sexes, and in the fact that the eggs are discharged into the sea by the females, and are there fertilised by the sperm discharged by the male oysters, instead of in the parent’s body.

Other “molluscs,” such as snails and whelks, enclose their fertilised eggs, when they lay them, in egg-shells. Some snails enclose a single egg in a shell which is filled up with clear liquid—corresponding to the “white” of a bird’s egg—in which the egg floats and develops. The eggs of the common snail are not bigger than a hemp-seed, but some Indian snails lay eggs as big as those of a robin, with a hard, calcareous shell, and the young snail has quite a large coiled shell of its own before it escapes from the egg-shell. So that it looks, when one of the big snail’s eggs is broken, as though a snail had managed to get inside a bird’s egg without making a hole in it! The whelks and their kind lay many eggs in one shell or capsule, and the sea-slugs produce a sort of firm jelly, in cords like vermicelli, the jelly enclosing hundreds of little sacs filled with liquid, in which the true germs or fertilised egg-cells float. These are all methods for protecting the young in their earliest condition. One of our pond-snails—the Paludina—keeps her eggs, whilst they develop, inside the dilated end of the tube which leads from the egg-producing organ or ovary to the exterior. The young snails nearest the opening to the exterior are the furthest advanced in development, and are as big as a dried pea. All stages, from the minute germ just fertilised to well-formed young, may be found in these snails, and the whole course of their development and gradual change and growth can be minutely studied with the microscope in one specimen.

Similar devices for protecting the young in their earliest helpless stages of growth from the egg-shell are found in all classes of animals. What is very curious is the fact that, of two closely allied animals, one species will recklessly lay its eggs and leave them, whilst another has special arrangements for retaining in the parent’s body the eggs as they develop, and so preserving them from danger. Such parents are called “viviparous.” Of course, in all viviparous animals, as well as in those which lay their eggs in hard shells, the fertilisation of the egg must be effected within the maternal body. Amongst our common fishes there is the viviparous blenny, often found in pools at low tide on the seashore. All the other British fresh-water and marine fishes lay their eggs and abandon them, excepting some sharks, dog-fish, and skates, which are viviparous; others of the shark and skate tribe lay eggs of large size encased in hard, horny shells. Every one knows that frogs and toads lay their eggs, but there are some kinds in which the eggs remain inside the mother’s body during the development of the young, which only escape into the world as well-formed little frogs. All the hairy, warm-blooded quadrupeds known as “the mammals” are viviparous, except the duck-mole and the spiny ant-eater of Australia. These extraordinary little “beasts” lay eggs like those of a bird.

The most ingenious devices for the protection of the young are (as perhaps those who believe in the superior intelligence of the male would expect) put into practice by the male parent. Thus, there is a large fish in tropical rivers which takes the eggs laid by the female into his capacious mouth, and swims about with them for three or four weeks, giving them the advantage of a current of water which runs through his mouth to his gills. When the young hatch they swim out of their fond father’s mouth. The male of pipe-fishes and of the little “sea-horse” receives the eggs laid by the female into a pouch excavated along his ventral surface. There the young hatch, and are guarded by the nursing father. On the other hand, some fathers impartially eat their own young, as well as those of other parents, and the mother has a hard job to protect her offspring. A female octopus (the poulp or eight-armed cuttle-fish) sits over her eggs in a nest built of pebbles at the bottom of the sea (or of an aquarium tank in the instance studied by me many years ago at Naples), and squirts a stream of pure sea-water over them. She resents the approach of a fish or a crab or a landing-net with splendid fury and recklessness of attack. Often the males of fishes, frogs, and birds guard the eggs, or guard the nest where the female is occupied in caring for the eggs or the young.

There are various species of oysters common in all parts of the world which are eaten as delicacies. Primeval (Neolithic) man ate oysters (the common sort) in Denmark in enormous quantity—great heaps of the discarded oyster-shells are found, buried among which are discovered stone axe-heads and bits of rude pottery. In the West Indies travellers relate that the oysters “climb” the trees which overhang the water of quiet creeks and inlets of the sea. The fact is that the branches of the mangrove trees dip into the water, and the young oyster “spat” attaches itself to the immersed twigs. After a year or two, the tree grows vigorously, and raises its branches up in its growth, so that the oysters are carried far up above the sea waves. Of course they die under these conditions, but their position suggests the explanation that the oysters have climbed up the trees. Ship barnacles fix themselves, similarly, to the twigs of willow trees in the quiet sea lochs of the West of Scotland, and this led 500 years ago to the belief that the catkins of the willow tree ripen into barnacles. Since it was also held that the little animal of the barnacle hatches out of its shell as a young goose—the so-called “barnacle goose”—the marvellous story was believed that these geese are actually budded from willow trees. I believe that the supposed relationship of the goose and the ship’s barnacle arose solely from the accidental similarity of the names of the two animals—the “bernack” goose and the sea “barnacle” being names of independent origin. The names were different originally in sound and signification, but were corrupted by fisher-folk into one and the same word. Hence a fantastic fable took its growth.

In Paris you may test and compare several local varieties of the common oyster in a celebrated oyster-shop. There are Courseilles, Cancales, Marennes, Ostend, Zeeland, Arcachon, English natives, CÔtes Rouges (red banks), and Black Rocks. And you can eat sea-urchins there, too, if you wish. They have not, however, got the celebrated oysters from the Lake Fusaro, near Naples. This was the ancient Acherusia palus, and in the neighbouring Lake Avernus and the Lucrine lake oysters were cultivated by the ancient Romans, the young oysters being made to affix themselves at “the fall of the spat” to wooden “stands” or frames, which were then placed in the lake (a salt-water lake), where they had abundant minute vegetable food and grew large and fat. The same cultivation, with the same shape of “stands,” is carried on at the present day in the Lake Fusaro. My friend, Mr. GÜnther, of Magdalen College, Oxford, has published pictures of Roman tiles from this neighbourhood showing the oysters adhering in rows to the wooden frames. These tiles were apparently sold to holiday visitors in the time of the Roman emperors as a memento of a happy day spent at the Lucrine lake, just as a sugar basin or a mug is now sold at our seaside resorts with the inscription, “A present from Margate,” or Southport, or Blackpool, and the picture of a shrimp above it.

The care of the breeding oyster and the plans adopted by the owners of oyster-beds for catching the “spat,” or young oysters, when they fall to the bottom, by placing movable tiles or frames for them to fix themselves to, form an important part of the craft of the oyster-man. It is a difficult business, and is variously carried out in England, France, Holland, and America. The young oysters, when they have fixed themselves, are carried on the movable tiles or frames from one region to another for the purpose of encouraging their growth and avoiding a variety of dangers to their life and health (sometimes from the Bay of Biscay to the mouth of the Thames!). They are often—but not always—finally fed up in sea-ponds or inlets, which are peculiar in containing an enormous number of those very minute microscopic plants, with beautifully shaped siliceous shells, which are known as diatoms. These are so abundant in such ponds as to form a sort of powder or cloud near the bottom, and the oysters draw them, day and night, by their gill-currents into their mouths, digest them, and grow fine and fat. The district of Marennes, on the west coast of France, is celebrated for having sea-ponds or tanks in which a wonderful diatom of a bright blue colour abounds; so abundant are they that the cloud produced by them in the pools is of a deep cobalt-blue. When oysters are placed in these tanks to fatten, their gills or beards become rich blue-green in colour. They lose the colour after ten days, when removed to ordinary tanks. These are the celebrated green oysters or “Marennes vertes” of French restaurants. The colouring matter of the little diatoms—swallowed by the million and digested—is taken up by the blood of the oyster from its stomach, and is excreted by certain corpuscles on the surface of the gills—as I showed some twenty-five years ago—just as red madder is deposited in the bones of a pig fed upon madder, and as the feathers of the canary take up the colour of cayenne pepper when it is mixed with the canary’s food. It used to be thought that the green colour of the green oyster is due to copper—and that opinion was supported by the curious fact that the blood of all oysters and other molluscs, and also of lobsters, scorpions, and king-crabs, does really contain a minute quantity of copper, just as our blood contains iron! It was also supported by the fact that occasionally a fraudulent fishmonger, when asked to supply green oysters, has been convicted of colouring the beards of ordinary oysters with green copper salt, so as to imitate the real article! The real history of the green-bearded oysters is now quite certain, and any one interested in the matter should look at the coloured pictures of the beautiful little blue-coloured Navicula ostrearia—the diatom on which this oyster feeds, published by me in the Quarterly Journal of Microscopical Science in 1885.