Natural oyster beds occur in every sea where the coast affords the proper conditions with a shelving and not too rocky bottom. In France the beds of Rochelle, Rochefort, the isles of Re and Oleron, the bay of St. Brieuc, Cancale and Granville are the most famous. On the Danish coast there are forty or fifty beds on the west coast of Schleswig, the best lying between the small islands of Sylt, Amzon, Fohr, Pelworm and Nordstrand. The oyster beds of England extend from Gravesend, in the estuary of the Thames and midway along the Kentish coast, and in the estuary of the Coluc and other small streams on the Essex coast. The Frith of Forth is also famous for its oyster beds. The product of these beds has diminished in recent times; according to some authorities from too improvident and persistent dredging, but Mr. Buckland attributes the decrease in the yield to sudden changes in the temperature at the critical period when the spat, or young oysters, are just formed, rather than to over-dredging.
The United States is more abundantly furnished with oyster beds than any other country. They extend along almost the entire coast. Those of Virginia are estimated to comprise nearly 2,000,000 of acres. The sea-board of Georgia is famous for its immense supplies, while the whole 115 miles of Long Island is occupied with them.
The oyster is one of the lowest forms of the mollusk. Its mouth opens right into its stomach, which is surrounded by its liver, permeated by a yellow liquid, the bile. It may thus be said that they have their stomach and intestine in the liver, the mouth upon the stomach and the opening of the intestine in the back. They have a heart which circulates a colorless blood. They breathe at the bottom of sea, having an organ which separates from the water the small amount of oxygen it contains. Their respiratory organs are two pair of gills, or branchiae, curved and formed by a double series of very delicate canals placed close together, resembling the teeth of a fine comb. This apparatus, like the mouth, is hidden under the fold of the mantle. They have no brain, but a ganglion of nerves, a whitish substance situated near their mouths. From this originate the nerves, which branch off to the region of the liver and stomach; here they re-unite in a second ganglion which is placed behind the liver. The nerves of the mouth and its tentacles originate in the first ganglion, those of the respiratory organs in the second. It has no sense of sight or hearing, the sense of touch is all that it has, and this resides in the tentacles of the mouth. Its taste, if it has any, must be very feeble. Its powers are most limited; imprisoned forever in its shell, it has no power of locomotion, and being without any distinction of sex, its wants or desires must be very few.
Still the oyster appears to be a social animal, and loves to gather together in great numbers, so that despite their apparently low grade of intelligence, we cannot say that they have not sympathetic feelings. Uniting as they do both sexes in each individual, the oyster's organs of reproduction are visible only at the period they are in use. Their young are produced from eggs, which are produced between the folds of their mantle, and in the midst of their respiratory organs. The number of these eggs is prodigious. According to some authorities the number produced by a single oyster reaches 10,000,000. Naturalists, however, at present consider this estimate too high, and limit it at about 2,000,000 for each individual. The eggs are yellow, are hatched in the mantle, and when the embryo leaves its parent it can breathe. The spawning time is from June to September. The oyster differs from most shell-fish in that when the young leave the parent they can support themselves; ordinarily the shell-fish throw out their eggs committing them to chance for their protection. In the spawning season an oyster bed is the most interesting place; each oyster is throwing out a whole array of descendants, filling the water with a cloud of living dust, so that the sea is clouded with the spat as it is called.
Under the microscope the spat is seen to be provided with a shell, and with vibratory cils which enable it to swim. When the current carries it against any stationary body, it immediately adheres to it, the cils disappear and the young oyster, becoming fixed, commences to develop. It takes three years for them to attain their full size. While the spat is swimming about, before becoming fixed, it is said that if anything alarm them they seek refuge again within the maternal shell. Such prolific production would soon stock the whole sea, were it not for the fact that the young are feeble swimmers, and that millions of them are annually swept away and lost by the current, or fall a prey to the numerous animals which feed upon them.
FAGGOTS SUSPENDED TO RECEIVE OYSTER SPAT.
The favorite place for the oyster is on the shore, in water not very deep and free from currents; here they are very prolific. The idea of breeding them is as old as the Romans, and to-day the planting of oyster beds, and fishing from them gives occupation to thousands. Some of the oyster beds of France which were nearly exhausted twenty years ago have been made again very productive by attention and care. The plan of suspending faggots upon which the spawn should adhere, has been found very successful. From the Bay of St. Brieuco two faggots, taken up at random, were found to contain about 20,000 young oysters, ranging in size from one to three inches in diameter. Their exhibition excited astonishment; they looked like leafy branches, each leaf being a living oyster.
In the island of Re oyster farming is in full operation. It is calculated that the beds contain 600 oysters to the square yard, the majority of marketable condition, making a total of 378,000,000 in these beds alone. In the United States, the productiveness of the beds is almost inestimable, and yet, despite the immense number of oysters yearly brought to market, the demand continually outstrips the supply. The modern methods of canning have opened a so much wider market, the whole inland country being thus opened to the supply, it is almost impossible to overstock the market.
The peculiar green color of the oysters in France, which have been planted in beds, or claries, and which is thought to make their flavor better, arises from some cause, concerning which naturalists differ. It seems, however, to be some kind of disease, arising from the condition of the water in these beds.