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CHAPTER III.

THE STRUCTURE OF SILVER-SHELL.

THE PHRASE STUPID AS AN OYSTER "-HEADLESS BEINGS-THE MANTLE OF SILVER-SHELL-THE STOMACH-THE LIVER-THE

HEART-THE BREATHING ORGANS-THE ORGANS OF NUTRITION.

SILVER-SHELL, taking to its bed, while we rise from ours, to gain a subsistence, may, at a hasty glance, be undervalued. "Stupid as an oyster" has become a proverb. Of this Shakespeare was cognisant, as is evident when Benedick, describing the strange change that had passed on Claudio, says-" He was wont to speak plain and to the purpose, like an honest man and a soldier, and now is he turned orthographer; his words are a very fantastical banquet-just so many strange dishes. May I be so converted, and see with these eyes ? I cannot tell; I think not; I will not be sworn, but love may transform me to an oyster; but I'll take my oath on it, till he have made an oyster of me, he shall never make me such a fool."*

It is said of some persons, "they have no head." Not that they are supposed to resemble the sign of

*"Much Ado about Nothing," act ii., scene 3.

"the good woman," which is still sometimes to be seen as a headless figure; much less that they walk abroad as the Parisians say St. Denis did, carrying his head in his hand. The declaration is evidently figurative, and denotes that such persons make no proper use of their heads, and act with so total a want of all thought and discretion, that it is as if they had actually none.

But to say an oyster has no head is to state a literal fact. Accordingly it is ranged by naturalists among headless beings;* and unquestionably it is manifestly inferior to those which are gifted with a brain. Such creatures, prepared for a higher order of instinct, often delight and astonish us; as the spider, when spinning its web on the garden wall with admirable precision; or the bees, in all the economy of the hive, subject as they are to the authority of a queenly presence, from which, like the attendants of a court, no one retires except by a backward movement. If, however, there are tribes of beings far superior to the oyster, it is still fully prepared for the condition it is destined to occupy. Its internal structure is admirably perfect, and, however regarded, it is obviously suited to a passive life. A creature designed for locomotion has evidences of existing things, sometimes to supply its wants, and at others to apprise it of danger; but of these the oyster is destitute, for, being destined to rely entirely on its fixed resources, any other powers would tantalise it in vain.

* Acalephæ.

Oyster in shell, the upper valve removed. a, upper portion of the mantle, covering the mouth with its four lips; b, c, the mantle; d, the breathing organs; e, portion of the lobes of the mantle, between which is the extremity of the intestinal canal; f, part of the heart; g, adductor muscles.

The body occupies the great concavity of the under shell (2), presenting to view a squared margin, opposite

to the hinge, and a projecting margin along its two sides. The surfaces of the body have a lacework of fat when the oyster is in good condition. The marginal borders, proceeding alike from the upper and under surfaces, are gradually extended as they advance towards the edges of the shells, and they form the outline of those extended membranes to which the names of the pallium, the coverlet, and the mantle have been given.

That a clear idea may be formed of this very remarkable portion of the oyster, it may be still further observed, that if one of these creatures be placed with its concave shell downwards, and having the hinge next the observer, the right and left sides will then be determined. The lower folds of the mantle then become united on the right side, nearly opposite to the muscular ligament, and they form an entrance to the interior of the branchiæ, or breathing organs, which has been termed the branchial porch. The mantle is free throughout its circumference, except a part of its margin on the straight side, where it forms a kind of hood.

The oyster has a mouth (6), placed at the narrowest part of the body-a simple orifice with no kind of teeth, but bordered by four thin lips, ranged on the two sides of the aperture, and is represented covered by a part of the mantle. The tube called the œsophagus, from two Greek words, meaning "I eat,"

and "to carry," and more commonly the gullet, is extremely short, so that in such creatures the mouth appears to open into the stomach.

The stomach is a kind of bag (3), placed immediately behind the opening of the mouth; and when, in any instance, the stomach is cut open, it will show the apertures of several large vessels, by which the bile is conveyed from the liver-an organ which entirely surrounds the stomach. The liver is very large, of a greenish and sometimes a dark chocolate colour.

Fig. 3.

Ex

ternally it exhibits a regular series of equal-sized granules (4), which may be shown by boiling the oyster, and then tearing off its loosened external covering. Internally it presents arborescent vessels, which converge into excretory ducts, as they approach the