The Book of Shells. Containing the Classes Mollusca, Conchifera, Cirrhipeda, Annulata and Crustacea

In reviewing the first Division of the animal kingdom, namely, the vertebral animals, we cannot fail to have been delighted with the wonderful and appropriate faculties bestowed upon each individual; but, beautiful and well adapted to the use of their possessors as these faculties may have appeared, our pleasure must be still greater in tracing the powers with which those creatures are endowed, which constitute what we have been accustomed to call the lower orders of animated nature.

When contemplating the graceful form of the horse or the stag, or the beautiful plumage of the feathered tribes, or when we notice the terrific appearance of the crocodile, or the elaborate finish and metallic lustre of the scales of fishes, we are led to expect that equal care has been bestowed upon the rest of the organization of the different individuals, and that equal attention has been paid to the various instincts and powers that are necessary to their preservation; but when we observe a snail, or a worm, and compare their more simple appearance, and the perfect absence of what we have been accustomed to consider the organs of motion, namely, feet and hands, we are apt to look on them as having been created for some very subordinate purpose, and, therefore, less carefully formed than the vertebral animals. How much greater then must be our delight, when we find them possessed of 

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every power necessary to their state of existence, as beautifully developed, and as carefully adapted to their necessities, as the highest instincts of other classes are to their possessors. Nor is their organization to be considered less perfect, because we are unable to trace it in all its ramifications; the minute branches of the nerves of the human body are, not only invisible to the naked eye, but even to the most acute observer when assisted by the magnifying power of the microscope, but we are certain that they do exist, from the pain we feel when they are injured. Until lately, the Infusoria, those microscopic animals that are found in infusions of vegetable substances in water, were supposed to be possessed of neither nerves nor stomach, and to be fed by absorption; but the ingenious experiments of a learned foreigner have proved, that, instead of being without a stomach, they are provided with as many as five or six: it is true, that the nerves have not yet been detected, but we have a right to infer their existence from their effects; so that these minute creatures, which we have been accustomed to consider as nearly destitute of organs, are, in fact, beautifully formed, and as perfect in their kind as any other of the Creator’s works.

The second Division of the objects of natural history, namely, the Invertebral animals, which we have now to describe, are placed by themselves, on account of their being without an internal skeleton, consisting of a series of vertebræ, or bones of the back. This distinction is explained in the introductory chapter to the Book of Animals. They have been separated, by Lamarck, into Eleven Classes, namely:—

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1. Mollusca, (soft-bodied animals,) in general covered with a shell; as, for instance, a snail; or without a shell, as a slug.

2. Conchifera, (shell-bearing animals,) with a shell, consisting of two valves, as an oyster or mussel.

3. Cirrhipeda, (with feet like cirri, or hairs.) The inhabitant of the acorn-shell, found on the back of the larger kind of shell-fish, &c., is an instance of this class.

4. Annelida, (with body formed of rings;) of this class the leech and the earth-worm are instances.

5. Crustacea, (covered with a hard case,) crabs, lobsters, &c.

6. Arachnidæ, Spiders.

7. Insecta, Insects. A perfect insect has always six legs.

8. Tunicata, (enclosed in a case of a leathery consistence.)

9. Vermes, Worms. With lengthened body without divisions; for instance, worms found in the intestines.

10. Radiariæ, (radiated animals,) with the different parts of which they are formed arranged like rays round one common centre; as, for instance, the Star-fish.

11. Polypi, (many feet.) The animal that forms the Coral is a Polypus.

12. Infusoria, (Infusory animals.) These are found in infusions of vegetable substances in water, and are, in general, too small to be visible to the naked eye.

In the present little book we shall treat of the first five of these Classes.

The Molluscous animals are, on account of their organization, placed first among the invertebral animals, a few of the species resembling, in some respects, the more simply-formed fishes.

The systematic arrangement of the Molluscous animals, considered not only as regards their shells, but having reference also to the anatomical distinctions of the creatures themselves, is a modern study. In ancient authors we merely find a few scattered facts, the beauty of the shells attracting their notice more than the value or nature of the animals.

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Although, at the first glance, the inhabitants of shells appear to be beings of a very uninteresting nature, a due consideration of the valuable properties of many, and the usefulness of all, will enable us to perceive, that, regarding them merely in an interested point of view, they are worthy of the strictest attention of the naturalist. In the first place, the whole of them afford food for the different species of fish, and other inhabitants of the deep. The Tyrian dye, the royal purple of the ancients, was produced by the inhabitant of a small univalve shell, of the genus Purpura. That beautiful ornament in dress, the oriental pearl, is the consequence of disease in a species of mussel, and the inner portion of the shell of the same animal, is the well-known substance, mother-of-pearl. A kind of silk is obtained from the beard of the pinna, which, in some places, is made into gloves. As an article of food we may mention the well-known oyster, the mussel, scallop, &c., and some of the larger kinds form no small portion of the subsistence of the natives of the South-Sea Islands, and the Negro population in the West Indies.

The Teredo navalis, or ship-worm, has, by its destructive powers, ruined the noblest vessels, and rendered useless the timbers, on which many of the constructions in harbours mainly depend for security; on this account great attention has been bestowed on its natural history and habits. The barnacle, which attaches itself to the bottoms of ships, renders the planks so foul, as to interfere materially with the rate of sailing of the vessel itself. These are only a few of the useful and noxious qualities of these inhabitants of the deep.

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The shell with which a Molluscous animal is covered, is absolutely necessary to protect its delicate body from injury; this shell is, in general, composed of much the same substances as bone; but the bone of a bird, or quadruped, is formed by the agency of the blood, and the particles of which it is composed are deposited by that fluid, and again taken up and restored to the circulation, a circumstance which does not take place in the substance of a shell. The shell is formed by the deposition of layer upon layer, in the course of the growth of the animal, and the ridges we perceive on many shells, point out their periodical increase.