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 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:—

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.)