ice, or in water. They continue thus till revived by the returning warmth of spring. They then become reanimated, change their skin, and appear abroad in a new coat. Many of them cast their skins frequently in the year; but Tortoises and some other Reptiles have an osseous covering which they do not change.

The Amphibia, though they are occasionally found in great numbers together, cannot be said to congregate, since they do nothing in common, and, in fact, do not live in a state of society. The flesh and eggs of some of the species constitute a palatable and nutritious food.

Of the Serpents. There is much geometrical elegance in the sinuous motion of the Serpent tribe. Their back-bone consists of movable articulations, and runs through the whole length of their body. The breast and abdomen are surrounded with ribs. Some of the species can render their bodies perfectly stiff, and by this means they are enabled to spring with great force and velocity on their prey.

Most of them are covered with scales; and Linnæus has endeavored to mark the different species by the number of scaly plates on the abdomen and beneath the tail. Experience, however, has proved, that these are too variable and uncertain to be depended on.

The head is connected to the trunk without the intervention of a neck; and their jaws are so formed that the animals are able to swallow bodies as thick and frequently even thicker than themselves. The tongue is slender and cleft.

The poisonous Serpents, which are not more than one sixth of the whole number of species, differ from the others in having long tubular fangs on each side of the head calculated to convey the venom from a bag or receptacle at the base of these fangs into the wound made by their bite. The venomous Serpents have only two rows of true or proper teeth, (that is, such as are not fangs,) in the upper jaw, whilst all others have four. A head entirely covered with small scales is also in some degree a character, but by no means a universal one, of poisonous species; as are also scales on the head and body furnished with a ridge or prominent middle line.

The Amphibia are divided by Linnæus into two orders: viz. Reptiles and Serpents The Reptiles are furnished with legs. They have flat and naked ears, without auricles. The principal tribes are, Tortoises, Lizards, and Frogs.

Serpents are destitute of feet. Their jaws are dilatable and not articulated; and they have neither fins nor ears.

FISHES.

Were we acquainted with no other animals than those which inhabit the land, and breathe the air of our atmosphere, it would appear absurd to be told that any race of beings could exist only in the water: we should naturally conclude, from the effect produced on our own bodies when plunged into that element, that the powers of life could not there be sustained. But we find, from experience, that the very depths of the ocean are crowded with inhabitants, which, in their construction, modes of life, and general design, are as truly wonderful as those on the land. Their history, however, must always remain imperfect, since the element in which they live is beyond human access, and of such vast dimensions, as to throw by far the greater part of them altogether out of the reach of man.

That they are in every respect, both of external and internal conformation, well adapted to their element and modes of life, we are not permitted to doubt. The body is, in general, slender, flattened at the sides, and always somewhat pointed at the head. This enables them, with ease, to cut through the resisting medium which they inhabit. Some of them are endowed with such extraordinary powers of progressive motion, that they are able not only to overtake the fastest sailing vessels, but, during the swiftest course of these, to play round them without any apparently extraordinary efforts.

Their bodies are in general covered with a kind of horny scales, to keep them from being injured by the pressure of the water. Several of them are enveloped with a fat and oily substance, to preserve them from putrefaction, and to guard them from extreme cold. They breathe by means of certain organs that are placed on each

FUNCTIONS OF FISHES.

25 side of the neck, and called gills. In this operation they fill their mouth with water, which they throw backward, with so much force as to lift open the great flap, and force it out behind. And in the passage of this water, among the feather-like processes of the gills, all, or at least the greatest part, of the air contained in it, is left behind, and carried into the body to perform its part in the animal economy. In proof of this fact, it has been ascertained that, if the air be extracted from water into which fish are put, they immediately come to the surface and gasp as if for breath. Hence, distilled water is to fish what the vacuum formed by an air-pump is to most other animals. This is the reason why, in winter, when a fish-pond is entirely frozen over, it is necessary to break holes in the ice, not that the fish may come to feed, but that they may come to breathe. Without such precaution, if the pond be small, and the fish be numerous, they will die from the corruption of the water.

Fishes are nearly of the same specific gravity with water, and swim by means of their fins and tail. The muscular force of the latter is very great. Their direct motion is obtained by moving the tail from one side to the other, with a vibrating motion; and, by strongly bending the tail sideways, this part of their body acts like the rudder of a ship, and enables them to move in an opposite direction. The fins of a fish keep it upright, especially the belly-fins, which act like feet; without these it would float with its back downward, as the centre of gravity lies near the back. In addition to the fins and tail, the air-bladder is of material assistance to fish in swimming, as it is by means of this that they increase or diminish the specific gravity of their bodies. When, by their abdominal muscles, they compress the air contained in this bladder, the bulk of their body is diminished, their weight compared with that of the water, is increased, and they consequently sink. If they want to rise, they relax the pressure of the muscles, the air-bladder again acquires its natural size, the body is rendered more bulky, and they ascend towards the surface. This bladder lies in the abdomen, along the course of the back-bone. In some fish it is single, and in others double. The air appears to be conveyed into it from the blood, by means of vessels appropriated to that purpose, and it can be discharged thence either into the stomach or the mouth. Those fish which are destitute of air-bladders have much less facility in elevating themselves in the water than any others. The greater number of them, consequently, remain at the bottom, unless the form of their body enables them to strike the water downwards with great force. This the Skate, the Thornback, and other species of Rays do with their large pectoral fins, which are of such size and strength as almost to resemble wings; and the mode in which these fish elevate themselves in the water, is precisely the same as that which is employed by birds in flying.

The teeth of fish are usually situated in their jaws: in some species, however, there are teeth on the tongue and palate, and even in the throat. These are generally sharp-pointed and immovable; but in the Carp they are obtuse, and in the Pike so movable as to appear fixed only to the skin. The tongue is in general motionless and fleshy. Being furnished with nostrils and olfactory nerves, there can be little doubt that fishes possess the sense of smelling.

The bones of these animals are formed of a kind of intermediate substance, between true bones and cartilages. The back-bone extends through the whole length of the body, and consists of vertebræ, strong and thick toward the head, but weaker and more slender as they approach the tail. The ribs are attached to the processes of the vertebræ, and enclose the breast and abdomin. Several fish, as the Rays, have no ribs; and others, as the Eel and Sturgeon, have very short ones. In many of the species there are small bones between the muscles, to assist their motion. The sight of fishes is perhaps the most perfect of all their senses. The eye, in general, is covered with the same transparent skin that covers the rest of the head; the use of which is probably, to defend this organ in the water, for none of the species have eyelids. The globe of the eye is somewhat depressed in front, and it is furnished behind with a muscle, which serves to lengthen or flatten it, as the animal may require. The crystalline humor, which in quadrupeds is flattened, is in fishes nearly globular. The eyes of fish are usually thought to be immovable, but this does not appear to be the case: those of some species are known to turn in the sockets.

In fishes the organ of hearing is placed at the sides of the skull; but differing in this respect from that in quadrupeds and birds, it is entirely distinct and detached

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26

ON THE STRUCTURE AND

from it. In some fishes, as those of the Ray kind, the organ of hearing is wholly surrounded by the parts containing the cavity of the skull: in others, as the Salmon and Cod, it is partly within the skull. In its structure this organ is by no means so complicated as in quadrupeds and other animals that live in the air. Some genera, as the Rays, have the external orifice very small, and placed upon the upper surface of the head; but in others there is no external opening whatever.

The food of these animals is extremely various. Insects, worms, or the spawn of other fish, sustain the smaller tribes; which, in their turn, are pursued by larger foes. Some feed on mud and aquatic plants, but by far the greater number subsist on animal food only, and they are so ravenous as often not to spare even those of their own kind. Innumerable shoals of some species pursue those of others through vast tracts of the ocean; from the vicinity of the pole sometimes even to the equator. In these conflicts, and in this scene of universal rapine, many species must have become extinct, had not the Creator accurately proportioned their means of escape, their production, and their numbers, to the extent and variety of the dangers to which they are exposed. The smaller species are consequently not only more numerous and prolific than the larger, but their instinct impels them to seek for food and protection near the shore, where, from the shallowness of the water, many of their foes are unable to pursue them.

Fishes are in general oviparous : some few, however, produce their offspring alive. The males have the milt, and the females the roe, but some individuals of the Cod and Sturgeon tribes are said to contain both. The spawn of the greater number is deposited in the sand or gravel: many of the fish, however, which reside in the ocean, attach their ova to sea-weeds. The fecundity of these tribes far surpasses that of any other race of animals. In the spawn of a single Cod upwards of nine millions of eggs have been ascertained, and nearly a million and a half have been taken from the interior of a Flounder.

The longevity of fish is far superior to that of other creatures; and there is reason to suppose that they are, in a great measure, exempted from disease. Instead of suffering from the rigidity of age, which is the cause of natural decay in land animals, their bodies continue to increase with fresh supplies; and, as the body grows, the conduits of life seem to furnish their stores in greater abundance. How long these animals continue to live, has not yet been ascertained. The age of man seems not equal to the life of the most minute species. In the royal ponds of Marli, in France, there are some particular fish which, it is said, have been preserved tame since the time of Francis the First, and which have been individually known to the persons who have succeeded to the charge of them ever since that period.

Fish, like land animals, are either solitary or gregarious. Some, as Trout, Salmon, &c., migrate to considerable distances in order to deposit their spawn. Of the sea-fish, the Cod, the Herring, and many others, assemble in immense shoals, and migrate in these shoals through vast tracts of the ocean.

In the Gmelinian edition of the Systema Naturæ, the Fishes are divided into six orders:

1. Apodal; with bony gills, and no ventral fins, as the Eels.

2. Jugular; with bony gills, and ventral fins before the pectoral ones, as the Cod and Haddock.

3. Thoracic; with bony gills and ventral fins placed directly under the thorax, as the Turbot, Sole, Perch, and Mackerel.

4. Abdominal; with bony gills, and ventral fins placed behind the thorax, as the Salmon, Pike, Herring, and Čarp.

5. Branchiostegous: with gills destitute of bony rays, as the Pike-fish and Lumpfish.

6. Chondropterygious; with cartilaginous gills, as the Sturgeon, Shark, Skate, and Lamprey.

FUNCTIONS OF INSECTS.

27

INSECTS.

The insect division of the animal world received its name from the individuals of which it is composed having a separation in the middle of their bodies, by which they are cut, as it were, into two parts. These parts are in general connected by a slender ligament or hollow thread.

Insects breathe through pores arranged along their sides; and have a scaly or bony skin, and many feet. Most of them are furnished with wings. They are destitute of brain, nostrils, and eyelids. Not only the place of the liver, but of all the secretory glands, is, in them, supplied by long vessels that float in the abdomen. The mouth is in general situated under the head; and is furnished with transverse jaws, with lips, a kind of teeth, a tongue, and palate: it has also, in most instances, four or six palpi, or feelers. Insects have also movable antennæ, which generally proceed from the front part of the head, and are endowed with a very nice sense of feeling.

In a minute examination of this class by Professor Cuvier, neither a heart nor arteries have been detected; and this gentleman says that the whole organization of insects is such as we might have expected to find, if we had previously known that they were destitute of such organs. Their nutrition, therefore, seems to be carried on by absorption, as is the case with the polypes, and other zoophytes.†

Nearly all Insects (except Spiders, and a few others of the apterous tribe, which proceed nearly in a perfect state from the egg) undergo a METAMORPHOSIS, or change at three different periods of their existence.

The lives of these minute creatures, in their perfect state, are in general so short that the parents have seldom an opportunity of seeing their living offspring. Consequently, they are neither provided with milk, like viviparous animals, nor are they, like birds, impelled to sit upon their eggs in order to bring their offspring to perfection. In place of these, the all-directing Power has endowed each species with the astonishing faculty of being able to discover what substance is fitted to afford the food proper for its young; though such food is, for the most part, totally different from that which the parent itself could eat. Some of them attach their eggs to the bark, or insert them into the leaves of trees and other vegetable substances; others form nests, which they store with insects or caterpillars that will attain the exact state in which they may be proper food for their young ones, when they shall awaken into life; others bury their eggs in the bodies of other insects; and others adopt very surprising methods of conveying them into the body, and even into the internal viscera of larger animals. Some drop their eggs into the water, an element in which they would themselves soon be destroyed. In short, the variety of contrivances that are adopted by insects to ensure the subsistence of their offspring, are beyond enumeration.

From the eggs of all insects proceed what are called larvæ, grubs, or caterpillars. These consist of a long body, covered with a soft, tender skin, divided into segments or rings. The motions of many of the larvæ are performed on these rings only, either in the manner of serpents, or by resting alternately each segment of the body on the plane which supports it. Such is the motion of the larva of Flies, emphatically so called, and of Wasps and Bees. Sometimes the surfaces of the rings are covered with spines, stiff bristles, or hooks, this is the case in Gad-flies. Crane-flies, and some others. The bodies of the larvæ, in some orders of insects, have, toward the head, six feet, each formed of three small joints; the last of which is scaly, and terminates in a hook: this is usual in those of Beetles and Dragon-flies. The larvæ of Butterflies and Moths, besides six scaly articulated feet, have a variable number of other false feet, which are not jointed, but terminate in hooks disposed in circles

* The Crab and Lobster tribes form an exception to this rule, for they respire by means of gills.

† He excepts the Crabs and Lobsters, which he arrangos in a class by themselves, and denominates Crustaceous animals.

and semi-circles. These hooks, which are attached to the skin by a kind of retrac. tile tubercles, serve as cramps to assist their motion on other bodies. The larvæ of such insects as undergo only a semi-metamorphosis, as Locusts, Crickets, and Cockroaches, and those of insects that undergo no transformation, as the Spiders, Ticks, and Mites, do not differ, with respect to their feet, from the perfect insects. In this larva state many insects remain for months, others for a year, and some even for two or three years. They are, in general, extremely voracious, oftentimes devouring more than their own weight in the course of twenty-four hours.

As soon as all their parts become perfected, and they are prepared to appear under a new form, called a pupa or chrysalis,* most species of insects fix upon some convenient place, for the performance of this arduous operation. This is generally a place where they are not exposed to danger; for in their transformation, they have neither strength to resist, nor swiftness to avoid, the attack of an enemy. That Power which instructed the parents to deposit their eggs in a proper receptacle, directs the offspring to the most secure and appropriate situation for their future defenceless state. Some of them spin webs or cones, in which they enclose themselves; others undergo their change in decayed wood; and others conceal themselves beneath the surface of the earth. Preparatory to the transformation, they cease to take any food, and, for some days, continue in a state of inactivity. During this time the internal organs are gradually unfolding themselves. When the completion is at hand, many of them may be observed alternately to extend and contract their bodies, in order to disengage themselves from the caterpillar skin. The hinder parts are those first liberated: when this is done, the animals contract, and draw the skin up towards their head; and, by strong efforts, they soon afterward push it entirely off. In their chrysalid state they remain for some time, to all appearance, inanimate; but this is only in appearance, for, on being taken into the hand, they will always be found to exhibit signs of life. It is singular that, in the changes of insects, the intestinal canal is frequently very different in the same individuals, as they pass through the three states.

As soon as the animal, within the shell of the chrysalis, has acquired strength sufficient to break the bonds that surround it, it exerts its powers, and appears to the world in a perfect state. For a little while it continues humid and weak; but, as the humidity evaporates, its wings and shell become hardened, and it soon afterward commits itself in safety to its new element.

Some writers have conjectured that the antennæ or horns of insects are their organs of hearing; for it is evident, from various experiments, that insects are possessed of this sense in a degree as exquisite as most other animals, although, from their minuteness, we perhaps may never discover by what means. The antennæ, however, seem little likely to answer the purpose of ears. These instruments, of apparently exquisite sensibility, appear adapted to very different purposes, but to purposes with which we may remain long unacquainted.

The eyes of insects are formed of a transparent crustaceous set of lenses, so hard as to require no coverings to protect them. These, like multiplying glasses, have innumerable surfaces, on every one of which objects are distinctly formed; so that, if a candle be held opposite to them, it appears multiplied almost to infinity on their surfaces. Other creatures are obliged to turn their eyes; but insects have always some or other of these lenses directed toward objects, from what quarter soever they may present themselves. All these minute hemispheres are real eyes, through which every thing appears topsy turvy.

M. Leeuwenhoek, with the aid of a microscope, used as a telescope, looked through the eye of a Dragon-fly, and viewed the steeple of a church, which was two hundred and ninety-nine feet high, and seven hundred and fifty feet from the place where he stood. He could plainly see the steeple, though not apparently larger than the point of a fine needle. He also viewed a house; and could discern the front, distinguish the doors and windows, and perceive whether the windows were open or shut. Mr. Hook computed that there were fourteen thousand of these lenses in the two eyes of a Drone; and M. Leeuwenhoek reckons twelve thousand five hundred and forty-four lenses in each eye of the Dragon-fly. The pictures of objects that are delineated on these, must be millions of times less than those formed on the

The chrysalis is occasionally called Aurelia, Bean, or Cod.