convulsed, and will not survive more than a few minutes.

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. When about to move itself, the fish turns the end obliquely to the water, and moves it through it in that position. The water re-acts obliquely against the tail, and moves him partly forward, and partly laterally. The lateral motion is corrected by the next stroke the contrary way, while the progressive motion is continued. Assisted by their tail, they turn sideways striking strongly with it on that side, and keeping it bent, it acts like the rudder of a ship. The fins of a fish keep it upright, especially the belly fins, which act like two feet: without these he would swim with his belly upwards, as the centre of gravity lies ncar the back. By contracting or expanding the fins, these also assist him in ascending and descending: by inclining his tail obliquely, and turning it a little from an erect position to one side, it helps him to rise and fall.

In addition to the fins and tail, the air-bladder is of material assistance to the 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 press the air contained in it, 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; but in the latter case the two parts communicate by a small canal. The air appears to be conveyed into it from the blood, by means of vessels appropriated to the purpose, and it can be discharged thence either into the stomach or the mouth. -Those fish that are without air-bladders have much less facility in elevating themselves in the water. The greater part of them remain at the bottom, unless the form of their body enables them to strike the water downwards with great force. This the Rays do with their large pectoral fins, which are sometimes, and not improperly, called wings, since the means which these fishes use in elevating themselves are precisely the same as those employed by birds in flying. When the bladder of a fish is burst, it is never afterwards able to rise. From a knowledge of this fact, the fishermen, after taking a quantity of Cod-fish, are able to keep them alive for a considerable time in their well-boats. They perforate the sound or air-bladder with a needle, disengage the enclosed air, and then throw them into the well, where they immediately sink to the bottom. Without this operation, they would not be able to keep them under water.

The teeth of fishes are usually situated in their jaws sometimes, however, they are found on the tongue or palate, and even in the throat. They are

generally sharp-pointed and immoveable; but in the Carp they are obtuse, and in the Pike so moveable as to appear fixed only to the skin.-The tongue is in general motionless, obtuse and fleshy; and in the Herring, and some other species, this is set with teeth, to enable them the better to retain their food. -Being furnished with nostrils and olfactory nerves, there can be little doubt of fishes possessing the sense of smelling.

The bones 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 towards the head, but weaker and more slender as they approach the tail. Each species has a determinate number of vertebræ, which increase in size with the body. The ribs are attached to the processes of the vertebræ, and enclose the breast and abdomen. Several fish, as the Rays, have no ribs; and others, as the Eel and Sturgeon, have very short ones. Between the pointed processes of the vertebræ lie the bones that support the anal and dorsal fins, which are connected with the processes by a ligament. At the breast lie the sternum, the clavicles, and the scapula, on which the pectoral fins are placed; the bones that support the ventral fins are called the ossa pelvis. Besides these there are often other 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 the greater part of them, is covered with the same transparent skin

that covers the rest of the head. The use of this is, probably, to defend it in the water, since there are no eyelids. The globe is somewhat depressed in front, and it is furnished behind with a muscle, which serves to lengthen or flatten it, according to the animal's necessities. The crystalline humour, which in quadrupeds is flattened, is in fishes nearly globular. The eyes are usually thought to be immoveable, but Gold Fish have been observed apparently to turn their eyes in their sockets, as their occasions require.-These fish take little notice of a lighted candle, though applied close to their heads; but on any sudden stroke against the stand, on which the bowl containing them is placed, they flounce about, and seem much frightened. This is more particularly the case when they have been motionless, and are perhaps asleep: from their eyes being always open, it is not, however, easy to discern when they are sleeping and when not.

In fishes the organ of bearing is placed on the sides of the skull, or the cavity that contains the brain; but, differing in this respect from that in quadrupeds and birds, it is entirely distinct and detached from the skull. 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 in part within the skull. In structure it is by no means so complicated as in the quadrupeds and other animals that live in the air. Some genera, as the Rays, have the external orifice very small, and

placed on the upper surface of the head; but in others there is no external opening whatever.

The food of these animals is almost universal in their own element. 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 part subsist on animal food alone; and they are so ravenous as often not to spare those of their own kind. Those that have the most capacious mouths pursue nearly every thing that falls in their way, and frequently meet in fierce opposition. The fish with the widest mouth is usually victorious, and he has no sooner conquered than he devours his antagonist. Innumerable shoals of some species pursue those of another 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 nature 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 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, as the Eel, and one of the species of Blenny, produce their young alive. The males have the