FUNCTIONS OF FISHES. 



17 



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 anj 

 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 tind, 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 tho 

 greater part of them altogether out of the reach of man. 



That they are in every respect, both of external and internal yonformatioa, 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 pro- 

 gressive 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 watei. Several of them are enveloped with a 

 fat and oily substance, to preserve them from putrefaction, and to guard them from 

 oxticme cold. They breathe by means of certain organs that are placed '■n eacli 

 ide 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 tlie feather-like pro- 

 cesses of the gills, all, or at least the greatest part, of the air contained in it, is left 

 behind, and carried into tho 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 »nd 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 en- 

 tirely 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. 



Fishos 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 tiuH 

 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 

 boiy 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. Tha 



