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OYSTER

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Originally appearing in Volume V20, Page 424 of the 1911 Encyclopedia Britannica.
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OYSTER . The use of this name in the See also:

vernacular is See also:equivalent to that of Ostrea (See also:Lat. from Gr. &rTaeov, oyster, so called from its See also:shell, 5omov, See also:bone, shell) in zoological nomenclature; there are no genera so similar to Ostrea as to be confounded with it in See also:ordinary See also:language. Ostrea is a genus of Lamellibranch Molluscs. The degeneration produced by sedentary habits in all lamellibranchs has in the oyster reached its most advanced See also:stage. The valves of the shell are closed by a single large adductor muscle, the anterior adductor being absent. The See also:muscular See also:projection of the ventral See also:surface called the See also:foot, whose various modifications characterize the different classes of See also:Mollusca, is almost entirely aborted. The two valves of the shell are unequal in See also:size, and of different shape; the See also:left See also:valve is larger, thicker and more See also:convex, and on it the See also:animal rests in its natural See also:state. This valve, in the See also:young oyster, is attached to some See also:object on the See also:sea-bottom; in the adult it is sometimes attached, sometimes See also:free. The right valve is See also:flat, and smaller and thinner than the left. In a corresponding manner the right See also:side of the animal's See also:body is somewhat less See also:developed than the left, and to this extent there is a departure from the bilateral symmetry characteristic of Lamellibranchs. The organization of the oyster, as compared with that of a typical lamellibranch such as Anodon (see See also:LAMELLIBRANCHIA), is brought about by the reduction of the anterior See also:part of the body accompanying the loss of the anterior adductor, and the enlargement of the posterior region.

The pedal ganglia and auditory See also:

organs have disappeared with the foot, at all events have never been detected; the cerebral ganglia are very See also:minute, while the parieto-splanchnic are well developed, and constitute dangerous. It acquired considerable application in See also:platinum the See also:principal part of the See also:nervous See also:system. See also:works, this See also:metal being only fusible in the oxyhydrogen See also:flame According to Spengel, the pair of ganglia near the mouth, and the electric See also:furnace; and also for the See also:production of limelight, variously called labial or cerebral, represent the cerebral pair as in See also:optical (magic) lanterns.

End of Article: OYSTER

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