WORMS.*

GENERAL ECONOMY.

Why are certain animals called invertebral?

Because they are destitute of skull and vertebral column, for the protection of the brain and the spinal

marrow.

Why are these animals furnished with crusts, scales, or hairs?

Because these appendices may supply the place of bones, and serve as a protection to the viscera, and as supports to the muscles. The blood, in those cases where a circulating fluid can be detected, is usually of a white or gray colour, seldom inclining to red.

Why are certain of these animals called mollusca? Because they are soft, (from molluscus, Latin) and have no skeleton. Their muscles are attached to their skin, and their nervous system is irregular in its form and distribution.

Why are others called annulosa?

Because they have the body divided into joints or rings, (from annulus, a ring) and, they either possess articulated feet or have certain processes which supply their place.

Why are some mollusca enabled to creep?

Because they alternately contract and relax the foot, or expand their muscles, which serve as suckers, and make their motion analogous to that of serpents.

Why do others swim?

Because they make serpentine undulations of the foot and body, or exert tentacula, or expanded portions of the integuments. Many species rise or sink in the water by aid of an organ somewhat resembling the

* Arranged in Six Orders:-1. Intestina-2. Mollusca-3. Testacea-4. Crustacea-5. Corallia-6. Zoophyta.

air-bladders of fishes. Others keep, or shift their position by a sudden jerk, produced by shifting the valves of the shell rapidly. The common scallop and the river mussel have the latter properties.

Why have some of these animals extraordinary power of suction?

Because they may fix themselves more securely; the sucker acting in the same manner as the moistened circular piece of leather, with a cord fixed to its centre, and applied to the surface of a stone. In the limpet, its surface is smooth and uniform; and the adhesion appears to depend on its close application to every part of the opposing surface. In other animals, as the leech and sea-urchin, the sucker is formed at the extremity of a tube; the muscular motions of which may serve to pump out any air which may remain, after the organ has been applied to the surface of the body. In a third class, the sucker is more complicated in its structure, consisting of many smaller ones, so disposed as to act in concert, as on the breast of the lump-fish. Neither quadrupeds nor birds possess any sucker. It is found among a few reptiles and fishes. The extremities of the toes of many insects possess complicated suckers. Among the mollusca and zoophytes, there are few in which suckers in some form do not exist. By means of this organ, whose power of cohesion must depend, not only on the extent of its surface, but the strength of the muscles which produce the vacuum, these animals can remain in the same spot, although acted on by forces to which their own weight could offer no adequate resistance. Pennant states that he heard of a lamprey, which was taken out of the Esk, weighing three pounds, adhering to a stone of twelve pounds weight suspended at its mouth.-Fleming.

Why are zoophytes considered the lowest family of animals?

Because they have not a heart or system of vessels,

THE EARTH-WORM.

Why is the earth-worm so called?

Because it swallows the soil or earth, from which, in its passage through the intestines, it extracts its nourishment.* Mr. Leon_Dufour has recently determined the earth-worm to be an oviparous and not a viviparous animal. The eggs resemble a chrysalis or a cocoon, but their pulp, &c. prove them to be true eggs.

The lower we go in the scale of creation, the more surprising is the reproductive faculty. The gardener cuts the earth-worm with his spade; but the injury, far from diminishing animal life, increases it; for each portion of the animal so divided, becomes a separate creature, having a system of parts speedily regenerated.

THE LEECH.

Why does the leech advance faster than other worms? Because the organs of adhesion are double, one at each extremity, the mouth adhering to one part of the surface, while the tail is brought up towards it, and is fixed, the body being at this time like an arch. The head then quits its hold, the body extends itself, and, when at full length, the head is then attached, and the tail brought up. By these alternate movements, the leech, at every step, advances nearly the length of its own body.-Fleming.

The stomach occupies the greatest part of the body in the leech, and is divided internally, by means of ten imperfect fleshy partitions, into somewhat separate portions.

* In a recent paper in the Foreign Quarterly Review we read of other earth-eaters, in South America, where the women, children, serpents, lizards, and ounces of the river St. Francisco have a singular and most economical propensity of eating earth. It seems that the soil contains a small portion of salt-petre, which is agreeable to the palate. Boys and girls, however, are less select in their tastes, and sometimes eat the whitewash off the walls, and occasionally, wood, charcoal, or cloth.

Why is the wound of the leech of three-sided form? Because within its mouth are three semicircular projected bodies, with a sharp toothed edge, with which it bites.

Why is a certain species called the flying leech?

Because it has the power of springing, by means of a filament, to a considerable distance. It is much smaller than the common leech; the largest, when at rest, not being more than half an inch long, and may be extended till it becomes a fine string; the smaller ones are very minute. It is common in the jungles in Ceylon; Bishop Heber tells us that "the native troops on their march to Canely, suffered very severely from the bites of flying leeches, occasionally even to the loss of life or limb: their legs were covered with them, and streamed with blood."

SNAILS.

Why do snails carry their shells with so much ease? Because they are bound to the shells by two muscles, which arise from the pillar, and having penetrated the body below its spiral part, run forward under the stomach, and spread their fibres in several slips, which interlace with those of the muscles proper to the foot, the substance of which they enter. It is obvious from this direction, that on their contraction, the body of the snail must be drawn within the shell. When it wishes to re-issue, the head and foot are forced out by circular fibres, which surround the body immediately above the foot.-Cuvier.

Blumenbach says "Whether the black points, at the extremities of what are called the horns of the common snail, are organs which really possess the power of vision, is still problematical."-Compar. Anat.

Why does the snail mark its track with a silver line of concrete slime?

Because the slime enables the slug to attach one part of its body more firmly to the surface on which