Page images
PDF
EPUB
[ocr errors]

surfaces a calcareous matter, which produces a shell around them.

Among the animals belonging to this class are the earth-worm, the leech, and the hair-worm.

The appearance of Earth-worms is familiar to all. They attain sometimes to the length of a foot, and have as many as a hundred and twenty rings, each of which is furnished with the little bristles or spines above mentioned. They emit through certain pores a slimy fluid, which lubricates their bodies, and thus gives them an easier passage through the earth, which they traverse in every direction. They feed upon roots, woody fibres, and the remains of animal and vegetable matter. They swallow earth also in considerable quantities, but this is probably on account of the animal, or vegetable matter, in a state of decomposition, which it may contain. When cut through the middle, each portion becomes a distinct individual. And in some worms nearly resembling the earth-worm, but residing in the water, the power of reproduction is nearly equal to that of the polypes.

The Leech has three jaws, or rather lancets, with which it pierces the skin of animals, in order to suck their blood. Its tail is furnished with a shallow cup or disk, by which it is able to fix itself firmly to different objects, while obtaining its nourishment in this manner; and by means of the same organ, it moves from place to place. There are several species of the leech, of which the medicinal is the most valuable, from the use made of it in local bloodletting. The horse-leech has the same power of drawing blood, but the wounds which it makes are sometimes followed by bad effects.

A

The body of the Gordius, or Hair-worm, is long, shaped like a thread or hair, nearly smooth, and round. It is a vulgar notion that the hair of the human head, or of a horse's tail, if thrown into the water, acquires life, and is converted into a worm. species of the hair-worm, in Africa and the Indies, is extremely noxious. It is of a pale, yellowish color, and is frequently met with among the grass, especially when covered with dew. It often insinuates itself into the naked feet or limbs of children and unwary persons, where it produces an inflammation that is some

times fatal. Great care and attention are required in extracting it; for if it be broken during the operation, the part which remains in the flesh continues alive, and is quite as troublesome as the whole.

CHAPTER VIII.

THIRD BRANCH OF THE ANIMAL KINGDOM.- MOLLUSCOUS ANIMALS.

UNDER this division are included a great variety of animals, of most of which the structure, residence, and habits are less perfectly known than those of the preceding classes. In their internal structure and organization, they are, for the most part, superior to the members of the division of Articulata, but as to intelligence and instinct, they are upon the whole inferior. Among them are the cuttle-fish, squid, oyster, clam, snail, and nearly all those commonly known as the testacea or shell-fish.

The Mollusca are destitute of bones and of articulated limbs. Their bodies are generally of a soft texture, and in many, at first sight, appear to be little else than a simple mucous mass, without parts, and almost without organization. Their muscles are fixed into the skin, which is naked, very sensible, and constantly moistened by a fluid furnished by its pores. The contractions of these muscles produce various motions of their whole bodies, often obscure and indistinct, by means of which, nevertheless, they are enabled to swim and crawl, or even seize those objects which are adapted to their nourishment. But as no part is supported by any solid foundation, like the bones of vertebral animals, their motions are for the most part slow, awkward, and limited.

Their bodies are generally covered by a fold or reflection of the skin, which envelops them completely, and is called their mantle. (Fig. 8, Oyster.) In some species, the two folds of the mantle are united at their edges, so as to form a complete bag,

in which the body of the animal is contained, opening only at one end by a sort of canal or snout: in some, it extends in two opposite directions, so as to answer the purpose of fins or oars. Sometimes there is only this simple membranous covering; but more frequently there is a hard external shell, which serves as a retreat into which the animal may withdraw itself, and which it can carry about upon its back in all its changes of place. These shells differ a good deal in shape, color, and texture, in different species; and among them are found some, whose form, polish, and splendid tints place them among the most beautiful objects in nature.

The

The Mollusca have no brain nor spinal nerve. Their nervous system consists merely of a number of masses, distributed in different parts of their bodies, from which are sent out a great many small branches, that mutually unite with each other. principal of these, which is sometimes called the brain, is situated around the oesophagus, and envelops it like a collar. In a few species it is contained in a cartilaginous case. Their respiration is not uniform. It is generally carried on by organs resembling the gills of fishes, which are acted upon either by fresh or salt water; but, in some cases, air is respired directly from the atmosphere. The circulation is double; that is to say, there is a passage of the blood through the respiratory organs, distinct from that through the rest of the body. by either one or more hearts. situated so as to receive the blood from the gills, and circulate it through the body. When there are two, the second is situated so as to circulate through the gills the blood coming from the body. In some species, there are three hearts; and in this case, as there are two sets of gills, a distinct heart is devoted to each. The blood in the Mollusca is thin, of a bluish white, and of the temperature of the medium in which they live.

This circulation is carried on When there is only one, it is

The organs of digestion vary very much. Sometimes there are organs for mastication, and sometimes not. Some species have only a single stomach, and others have several; the structure of this organ, in some species, very much resembling that of the gizzard of birds. In some species there are four stomachs, which bear a great analogy to those of the ruminating animals,

and have been supposed to answer a similar purpose. In the intestines there is as great a variety.

This branch is divided into several classes, according to the general form and structure of the species composing it. A few of the most important particulars that distinguish some of them will be pointed out..

In the first class, containing the cuttle-fish, squid, and nautilus, the body consists of a sack formed by the mantle, enveloping all the parts except the head, which projects from it, and is provided with a number of fleshy arms or feet, tapering towards their end, frequently of great length and of great power. These arms are capable of being moved in every direction, and are furnished with a large number of suckers in the form of cups, by which the animal can attach itself very closely to whatever object it embraces. They serve for swimming, for creeping, and for seizing prey. In all its motions, the head goes last, so that the animal in a manner pushes itself backward in whatever direction it wishes to move. Between the arms is placed the mouth, which is furnished with two strong jaws of a horny texture, and in shape resembling the beak of a parrot.

Some of these animals have the power of ejecting a peculiar liquid of a black color, when in any danger, for the purpose of discoloring the water of the sea around them, and thus concealing themselves from their enemies. The cavity containing this liquid is situated in the abdomen, and is sometimes found in the very substance of the liver. It has been supposed, that the celebrated paint called Indian ink, is made by the Chinese from. the inky fluid of some animal of this kind.

Their eyes are large and perfect. They have an ear; but no organ for smelling has been discovered, although they probably possess that sense. Their nature is fierce and cruel. They are very voracious, and devour great numbers of fishes and other aquatic animals.

Some of these animals grow occasionally to a great size. This is more particularly the case with the eight-armed cuttlefish. In the Indian seas, it is popularly supposed to attain to such a magnitude, that its arms are nine fathoms in length, and the other parts of its body large in proportion. The natives hold

.

it in great dread, fearing that it will lay hold of their boats, and drag them under water. They keep themselves provided with hatchets, to cut off its arms, should any danger arise from this

cause.

In another class, which includes the snail and the greater part of cockles, the foot, or instrument of motion, is placed under the belly of the animal, and consists of a fleshy plate or disk, protected underneath by a layer of a horny or calcareous substance, which, when the animal retreats into its shell, serves to close up its opening. Their mantle is fixed upon the back, and covers more or less of the body, the head also being partly enveloped by it. The mouth has generally a few tentacula or feelers beneath it, but they are sometimes wanting. The eyes are very small, sometimes fixed to the head, and sometimes situated upon the end of the tentacula; but they are also sometimes wanting. These animals are almost always furnished with shells, which serve them as a residence.

The Mollusca of another class, including the oyster, the clam, the quahaug, the mussels, and, in short, all the bivalve shell-fish, have no apparent head, but only a mouth surrounded by four tentacula, and situated beneath the folds of their mantle. The mantle is generally composed of two folds, which inclose the body between them, as a book is contained within its covers. Sometimes the edges of the two folds are united together, and form a complete sack. In the common clam, this sack terminates in a long, double, fleshy tube, which is usually called the head of

* A curious but perhaps apocryphal account of an enormous animal, which was probably of this kind, is found in the works of Pliny, who cites it from a writer named Trebius. This animal made its appearance on the coast of Cartein, and was in the habit, during the night, of robbing of their contents certain reservoirs of salt fish, which were situated near the seaside. Its depredations were not prevented by a row of stakes which were so planted as to intercept communication with the sea. It was found that the animal made use of a tree, which grew near the stakes, to assist it in climbing over them, and it was finally attacked, while in the reservoir, by a number of dogs and men. It made a powerful resistance, and lashed the dogs smartly with its arms, but was finally killed. Its body was as big as a hogshead; its arms, called its beards, were as big as a man could clasp, and thirty feet long; and its cups or suckers held four gallons each. It weighed 700 pounds. The popular belief in an animal called the Kraken may have been derived from the appearance of very large specimens of creatures of this description.

« PreviousContinue »