FISH. 



475 



other hand, is one complete structure, actuated by 

 a single principle, and having all its parts adapted to 

 each other with a perfection of scientific principle 

 which it would be vain for man to attempt imitating-, 

 except at the most humble distance. The fish does 

 not bend the posterior part of its body right and left 

 upon a single point, but brings it to a curve by an 

 immense number of vertebrae ; and in many species 

 the pieces composing this vertebral column are in 

 themselves so flexible, that the support of the muscles, 

 or that which is moved in the striking of the fish 

 right and loft as it swims, may be compared to an 

 elastic rod. But there is also something farther and 

 more beautiful in this piece of mechanism. The 

 muscles, or moving forces, are placed in flakes 

 attached to cartilaginous septa or divisions, which 

 proceed in an oblique, and generally in a curved 

 manner, from the vertebral column and its processes, 

 to the skin on each side ; and this succession of 

 muscular flakes is continued, not only the whole 

 length of the posterior part which we have supposed 

 to have the chief motion in ordinary swimming, but 

 from the base of the skull to the caudal fin. The 

 individual fibres of those muscles are placed, generally 

 speaking, in a longitudinal direction, and their con- 

 traction bends the whole fish in a graceful curve 

 towards the contracting side ; and in cases of great 

 exertion this curve may become an entire semicircle, 

 nay, almost an entire circle with the muzzle touching 

 the extremity of the tail, as may often be seen in a 

 salmon when it attempts to lea)) a cascade of consi- 

 derable elevation ; nor would one readily believe, 

 without actually seeing it, the height to which the 

 unbending of this curvature by the action of the 

 muscles on the other side can project the fish. This 

 leap is of course taken laterally through the air; and 

 so must be the leap of every fish when it rises to a 

 considerable height out of the water that is to say, 

 the fish must project itself " broadside on," but it is 

 very remarkable that when it falls in the water, a cat 

 does not fall more certainly upon its feet than a fish 

 falls in that attitude of the body which is natural to 

 it in swimming. It is further not a little curious, 

 that if the fish falls upon land or on a rock, it does 

 not right itstlf in this manner, but rather alights on 

 the side, as may be observed of leaping salmon when 

 they fall on the banks, or of flying fishes when in 

 their attempts to escape from their pursuers they 

 alight on the decks of ships. The mechanical action 

 of fishes is, however, a matter which has been but 

 little investigated ; and though from the variety, the 

 freedom, the rapidity, and very often the gracefulness 

 of their motions, it is a subject fraught with a vast 

 deal of mechanical information, it is one which, 

 however desirable it would be, we cannot for obvious 

 reasons prosecute further in a popular work. 



PUINCU-AL OUGANS OF FISHES. We shall give 

 very shoit notices of the principal systems of organisa- 

 tion in the finny tribes, and leave the reader to 

 ralise them. They may be conveniently brought 

 under the heads of support, protection, sensation, 

 motion, adhesion, respiration, circulation, nourish- 

 ment, and reproduction ; for we may pass over the 

 ins of absorption and secretion, and refer the 

 electric powers which are possessed by certain fishes 

 to the particular descriptions of the Gj/nniotits, the 

 Torpedo, and the various other species which have 

 this property. 



System oj support. This system consists of bones, 



as it does in the other vertebrated animals"; but the 

 bones are of a softer consistency. Even the hardest of 

 those which properly fcrm parts of the skeleton, are 

 to a great extent cartilaginous, and thus flexible, 

 while others contain very little salt of lime. This 

 affords a good general division of fishes into two very 

 distinct and well marked sub classes ; bony fishes, or 

 those which have the bones more or less firm, and 

 cartilaginous fishes, which have the bones flexible. 



It would be foreign to our purpose to enter into a 

 minute description of the skeleton, or indeed of the 

 anatomy of any part of the fishes, and the subject is 

 by no means an easy one, even for those who devote 

 their chief attention to the structure of animals. The 

 skeleton is in general very complicated, though com- 

 paratively concentrated into one mass, as compared 

 with that of land animals, but the greater number of 

 the articulations or unions of the pieces are quite dif- 

 ferent from these ; and it is only in the jaw-bones 

 and the dorsal and anal fins that we meet with any 

 thing that can, properly speaking, be called a joint, 

 or which consists of the motion of one bone imme- 

 diately upon another. In every other part of the 

 skeleton, the two adjoining pieces of bone are united 

 by a greater or smaller extent of cartilaginous sub- 

 stance ; and it is the yielding of this substance which 

 forms the bending of the articulation, so that there is 

 in the joint itself a certain degree of tendency to 

 spring back again when it is bent, without muscular 

 exertion. In mammalia and birds, the state of repose 

 is a certain degree of flexure in which the joints are 

 relaxed, and can be moved to some extent either way. 

 by very little external force ; but the repose of the 

 fish implies perfect straightness in the spinal column, 

 and there is no relaxing either way, because all the 

 muscles are equally in a state of repose, and the 

 joints are held in an even state by the action of the 

 cartilage alone. There is, perhaps, no animal in 

 which rest is so complete and perfectly without effort 

 or pressure upon any part of the body more than 

 another, as in a fish when it is motionless in the 

 water. The specific gravity of that fluid is of course 

 exactly equal to that of the reposing fish, otherwise 

 the fish would either sink downwards or rise up- 

 wards ; and the water presses equally upon it in every 

 part, so that it is impossible to conceive a kind of 

 suspension more favourable to perfect inaction or 

 waste of the system in any way, and this perfect rest 

 is probably one of the reasons why fishes are capable 

 of so much exertion at other times, and also why they 

 appear to have unlimited powers of growth and 

 endurance. 



In taking the simplest view possible of the skeleton 

 of fishes, we may consider it as consisting of a cranium, 

 a spine, and ribs, together with the bones that sup- 

 port the lateral, the dorsal, and the anal fins. The 

 cranium, or bones of the head, has no investment but 

 the skin, and therefore its form is easily seen. It 

 often consists of a vast number of pieces, but these 

 generally soon become soldered together. The head 

 is, generally speaking, united to the vertebral column 

 by a single' tubercle, and it has very little motion; 

 few of the osseous fishes have any vertebra which 

 can be called a neck, but some have, as, for example, 

 the common herring, in which there are four. In 

 the cartilaginous fishes the vertebra of the neck are 

 generally soldered into one general piece. In the 

 rest of the column the dorsal and caudal vertebra are 

 easily distinguished from each other, as the latter 



