The Oyster belongs to those Mollusks which are headless, having their gills in the form of membranous plates, and are named Lamellibranchiata, from the Latin word Lamella, a plate; or Conchæ, the Latin name for the whole family of oyster, scollop, cockle, mussel, and other well-known bivalves. Properly speaking, only six kinds are fit to take part in the gastromal treat, to say nothing of the sanitary advantages the family are good enough to provide for the world at large. These six peculiar and most agreeable aristocrats all belong to the family of the common oyster, Ostrea edulis, by far the most important tribe, and in fact, that in behalf of whose meritorious qualities I have more particularly taken up my pen.
The oyster bears different names in accordance to the localities in which it is found, whether on rocky ground, mud, or sand, and has different colours in different places. In Spain, oysters are found of a red and russet colour; in Illyria they are brown, but the fish is black, and in the Red Sea, of the colours of the rainbow. The green oyster, the Parisian delicacy, is brought from Brittany; but the same flavour and colour can be produced by putting oysters into pits where the water is about three feet deep in the salt marshes, and where the sun has great power. In these they become green in three or four days; for these colours are derived from the elementary substance on which they feed; not, however, that it produces any peculiar difference as to flavour. I may, however, as well decide at once that the green oyster is, to my taste, the oyster par excellence, in which decision I shall doubtless be borne out by most gourmets whose knowledge extends to a choice of the good things of this life.
I know, in this, some of my friends north of the Tweed may differ, and, if still living, amongst them I should have had to include Professor Wilson, so long the very life and soul of oyster-suppers and whisky-toddy. But nobody can judge of the true flavour of an oyster without well masticating his delicious food; and, by his own showing, both he and the "Shepherd" bolted their "Pandores." These same "Pandores," by the way, are large fat oysters, much relished in modern Athens, which are said to owe their superior excellence to the brackish contents of the pans of the adjacent salt-works of Prestonpans flowing out upon the beds. Taken away young and transferred to the Ostend beds, these Pandores furnish the very best oysters to be met with on the Continent, surpassing even the far-famed ones of Flensburg, in Holstein. Had "Christopher North" tickled the fish first to death with his incisors before he swallowed it, I might have submitted my judgment to his; but how can a man who bolted his food be quoted as an authority in matters of taste? At best, his must have been but an after-taste, a mere bilious reminder of what the repast had been, in which the whisky played as prominent a part as the "breedy creatures" themselves.
But let us return. The lower shell (*) of the oyster is concave, the upper flat. These shells are opened and closed by the medium of a strong muscle acting upon a hinge (+), far more complete in its structure than ever locksmith could produce, even at the forthcoming Exhibition of all Nations.
On the outside of the shell, when placed in a dark place, we may often observe a shining matter of blueish 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 light is produced by three varieties of minute animalcules, most interesting when examined under the microscope.
The oyster possesses an organ of respiration similar to that of a fish—branchiæ or gills, in fact (br), which are fringed by a mantle or beard divided into two lobes (m), filled up by small membranous fibres which terminate in the mouth (b), in the form of rays, serving the animal also with power to catch and eat. Unlike other shelled mussels the oyster has no feet; thus it is unable to make any other voluntary movement, save that of opening and closing its shell, as already named, in order to receive its food, which consists principally of small microscopical spores and young shoots of marine plants, made soft and thin by the action of the waves; whence arise the green beards or mantles. With some difficulty I have been enabled to separate a small portion of this vegetation from the mantle of an oyster, and having placed it under a strong microscope, discovered sea weed, of precisely the same species as that in which oysters are packed. They also feed on an infusion of sea worms called oyster animalcules. These are very accurately described in the "Journal des Savans," by M. Auzout. Some are irridescent, but others are not, and good specimens of all may be secured immediately the oyster has been taken from the sea.
By means of the beard or mantle described (m), the oyster secures his food, bringing it gradually, by means of little hooks bent inwards, to its mouth (b), wherein it is crushed and slowly consumed.
The stomach (i) is situated near the mouth, and all the organs are very simple. The mantle (m and m') above-named replaces the lungs. The liver (f) is small; the gall, comparatively speaking, large; the larger blood vessels little rarefied. The heart (h) consists of two cameras at a tolerable distance from one another, resembling small round bladders. The pulse beats rather slowly (caused by, perhaps, the want of food and sea water). From the stomach the rectum (a) leads directly to the anus. How digestion is effected in this short and simple way, I can scarce venture to assert. But it is a fact well known, that, after the spawning season, the oyster becomes thin, but a very short time enables it to recover its fat and succulence.
On examining the oyster the mantle (m), divided into two lobes (m and m'), the edges of which are fringed, will be perceived filling the greater part of the shell; also four membranous leaves crossed with stripes, which at their hinder extremities have as many capillary tubes. These leaves, or veins, unequally divided around the edges of the body perform the functions of the lungs, and separate from the water the necessary air for the maintenance of the animal.