[Illustration: THE PRAWN.]

THE PRAWN.—This little fish bears a striking resemblance to the shrimp, but is neither so common nor so small. It is to be found on most of the sandy shores of Europe. The Isle of Wight is famous for shrimps, where they are potted; but both the prawns and the shrimps vended in London, are too much salted for the excellence of their natural flavour to be preserved. They are extremely lively little animals, as seen in their native retreats.

[Illustration]

FISH.

CHAPTER VII.

THE NATURAL HISTORY OF FISHES.

199. IN NATURAL HISTORY, FISHES form the fourth class in the system of Linnaeus, and are described as having long under-jaws, eggs without white, organs of sense, fins for supporters, bodies covered with concave scales, gills to supply the place of lungs for respiration, and water for the natural element of their existence. Had mankind no other knowledge of animals than of such as inhabit the land and breathe their own atmosphere, they would listen with incredulous wonder, if told that there were other kinds of beings which existed only in the waters, and which would die almost as soon as they were taken from them. However strongly these facts might be attested, they would hardly believe them, without the operation of their own senses, as they would recollect the effect produced on their own bodies when immersed in water, and the impossibility of their sustaining life in it for any lengthened period of time. Experience, however, has taught them, that the "great deep" is crowded with inhabitants of various sizes, and of vastly different constructions, with modes of life entirely distinct from those which belong to the animals of the land, and with peculiarities of design, equally wonderful with those of any other works which have come from the hand of the Creator. The history of these races, however, must remain for ever, more or less, in a state of darkness, since the depths in which they live, are beyond the power of human exploration, and since the illimitable expansion of their domain places them almost entirely out of the reach of human accessibility.

200. IN STUDYING THE CONFORMATION OF FISHES, we naturally conclude that they are, in every respect, well adapted to the element in which they have their existence. Their shape has a striking resemblance to the lower part of a ship; and there is no doubt that the form of the fish originally suggested the form of the ship. The body is in general slender, gradually diminishing towards each of its extremities, and flattened on each of its sides. This is precisely the form of the lower part of the hull of a ship; and it enables both the animal and the vessel, with comparative ease, to penetrate and divide the resisting medium for which they have been adapted. The velocity of a ship, however, in sailing before the wind, is by no means to be compared to that of a fish. It is well known that the largest fishes will, with the greatest ease, overtake a ship in full sail, play round it without effort, and shoot ahead of it at pleasure. This arises from their great flexibility, which, to compete with mocks the labours of art, and enables them to migrate thousands of miles in a season, without the slightest indications of languor or fatigue.

201. THE PRINCIPAL INSTRUMENTS EMPLOYED BY FISHES to accelerate their motion, are their air-bladder, fins, and tail. By means of the air-bladder they enlarge or diminish the specific gravity of their bodies. When they wish to sink, they compress the muscles of the abdomen, and eject the air contained in it; by which, their weight, compared with that of the water, is increased, and they consequently descend. On the other hand, when they wish to rise, they relax the compression of the abdominal muscles, when the air-bladder fills and distends, and the body immediately ascends to the surface. How simply, yet how wonderfully, has the Supreme Being adapted certain means to the attainment of certain ends! Those fishes which are destitute of the air-bladder are heavy in the water, and have no great "alacrity" in rising. The larger proportion of them remain at the bottom, unless they are so formed as to be able to strike their native element downwards with sufficient force to enable them to ascend. When the air-bladder of a fish is burst, its power of ascending to the surface has for ever passed away. From a knowledge of this fact, the fishermen of cod are enabled to preserve them alive for a considerable time in their well-boats. The means they adopt to accomplish this, is to perforate the sound, or air-bladder, with a needle, which disengages the air, when the fishes immediately descend to the bottom of the well, into which they are thrown. Without this operation, it would be impossible to keep the cod under water whilst they had life. In swimming, the fins enable fishes to preserve their upright position, especially those of the belly, which act like two feet. Without those, they would swim with their bellies upward, as it is in their backs that the centre of gravity lies. In ascending and descending, these are likewise of great assistance, as they contract and expand accordingly. The tail is an instrument of great muscular force, and largely assists the fish in all its motions. In some instances it acts like the rudder of a ship, and enables it to turn sideways; and when moved from side to side with a quick vibratory motion, fishes are made, in the same manner as the "screw" propeller makes a steamship, to dart forward with a celerity proportioned to the muscular force with which it is employed.

202. THE BODIES OF FISHES are mostly covered with a kind of horny scales; but some are almost entirely without them, or have them so minute as to be almost invisible; as is the case with the eel. The object of these is to preserve them from injury by the pressure of the water, or the sudden contact with pebbles, rocks, or sea-weeds. Others, again, are enveloped in a fatty, oleaginous substance, also intended as a defence against the friction of the water; and those in which the scales are small, are supplied with a larger quantity of slimy matter.