478 



FISH. 



shoulder, and on various other places ; and when a 

 large spine of this description is observed upon any 

 part of a fish, it is always prudent to keep out of the 

 way of it, so long 1 as the fish is alive, as no animal, 

 either of the sea or the land; is ever furnished by 

 nature with a weapon without being at the same time 

 endowed -with the faculty of using it in the most 

 effective manner. Even the lesser weever, which is a 

 little thing about five inches long, will strike upwards, 

 or right and left, and inflict very painful wounds 

 with the spine of its dorsal fin, small as it is. 



Organs of motion. We have already alluded to this, 

 both in the fins and in the muscles by which these 

 are put in motion ; we shall therefore merely make 

 one or two general remarks here. Every one who 

 examines the muscular structure of a fish, and ob- 

 serves that each side of the whole body, from the 

 nape to the tail fin, consists of a rough mass of 

 muscle, cannot fail to perceive the great advantage 

 that arises from the division of this mass into so 

 many different flakes, each of which is really a 

 separate and independent muscle, receiving its own 

 nerves and vessels from the spinal column without 

 being in the least dependent on the others, and yet 

 all of which can act miscellaneously and in concert 

 whenever such action is necessary. So also, in con- 

 sequence of this division of the mass into independent 

 short lengths, the greater part of the fish may become 

 not a paddle merely, with the fin on the tail, but an 

 action something analogous to that of a many-oared 

 cutter, striking right and left at the same time, and 

 thus making the way of the ^animal in a perfectly 

 straight line, while it is apparently turning along like 

 a corkscrew. We have a very neat example of this 

 in the common eel, the motions of which are close, 

 but performed apparently in the most smooth and 

 easy manner imaginable, and with the least possible 

 fatigue. Then if there is a cross current to contend 

 with, or anything else that causes more resistance on 

 the one side than on the other, the greater power of 

 the action can instantly be thrown where the greater 

 effort is required, and the fish can keep its course 

 without drifting, where any other creature would be 

 completely at the mercy of the current. 



Nor must we overlook the advantage of this ac- 

 cumulation of muscles in the event of any local 

 injury taking place. The limbs of mammalia, and 

 the wings of birds, are in their several articulations 

 dependent on few muscles, and those of the one joint 

 do not assist those of the other, so that if one is ren- 

 dered unserviceable the whole limb is crippled. But 

 in the compound muscle of a fish, though one or 

 more of the flakes happen to be deeply wounded, 

 there are still many others performing the very same 

 office, and thus a very severe wound in one place 

 will not greatly lessen the swimming power. This is 

 of great service to fishes as a protection against each 

 other. As is usually said, the fishes "care not a 

 rush for the weather, but make themselves happy in 

 eating one another whether it is foul or fair." Now 

 this is very nearly, if not altogether, the literal fact of 

 the case ; and so, when numbers of them are con- 

 gregated together in one place, and the shoals often 

 amount to many millions, numbers of them must be 

 constantly getting bit.es ; and if they were as much 

 affected as land animals are when bitten or torn, the 

 sea would literally be encumbered with crippled fish. 

 Anglers often catch a trout or a salmon which pro- 

 bably an otter has made pay the forfeit of nearly a 



pound of flesh, and yet, with a great notch in his 

 back, if it does not reach down nearly to the spinal 

 cord, a fish will take the bait, or rise to the fly with 

 nearly the same alacrity as if his skin was whole. 



There is one other consideration worthy of notice 

 with regard to the general condition of the organs of 

 motion in fishes. They have really less work to do 

 than the organs of any other animals, not excepting 

 their neighbours of the deep. The Crustacea have a 

 dead weight to carry ; and, in the cae of a crab or a 

 lobster, this dead weight forms no small fraction of the 

 whole. So also the shelled mollusca have often to 

 carry about five times their own weight in the house 

 which they make for themselves ; and this house is 

 always specifically heavier than sea water, so that 

 those which rise to the surface require a particular 

 apparatus for floating it upwards. Land animals have 

 also their own weight to carry ; which, making allow- 

 ance for difference of structure, appears to be almost 

 equally laborious in those which walk and those which 

 fly. But a fish has no weight to carry ; for though, 

 of course, the total pressure of the water increases 

 with the depth, the specific gravity varies but little, 

 because water is not much compressible ; and from 

 what we experience ourselves when exposed to dif- 

 ferent degrees of atmospheric pressure, we can readily 

 understand that a fish may be as comfortable under 

 the pressure of a hundred atmospheres of water, as a 

 land animal is under that of the light atmosphere of a 

 mountain top. Thus the only exertion which a fish 

 requires to make is that which conducts it from place 

 to place, either in search of its food, or on those jour- 

 neys which many fishes perform seasonally, chiefly 

 with a view to breeding. This appears to be the rea- 

 son why fishes have so few blood vessels in the mus- 

 cular parts of their bodies. From what we know of 

 circulation, we may safely conclude that the waste of 

 the system, or of any part of the system, is in propor- 

 tion to the number of blood vessels, and the quantity 

 of blood which circulates through them. Now birds, 

 and especially mammalia, have those vessels so com- 

 pletely ramified through every part of their bodies, 

 except the solid bones (and there is blood in vari- 

 ous bones of the mammalia when young), the tendons 

 and the simple membranes, that no part of their system 

 can be lacerated, or even scratched, without the effu- 

 sion of blood, for the skin itself is full of blood vessels ; 

 but before red blood can be obtained from a fish, the 

 wound must be a pretty deep one, unless it is given 

 through the tissue of the gills, through which the blood 

 passes. We have already mentioned the names and 

 situations of the principal fins ; and so we have only 

 to say a few words upon the difference of position in 

 the abdominal ones, which are those that most difl'er 

 in position ; and this is all that is necessary to be at- 

 tended to in a general glance, because the relative 

 shape and degree of development in the different 

 fins properly form part of the particular descriptions 

 of the races. Now, in those species which have the 

 ventral fins placed backwards, we generally find that 

 the usual line of motion in swimming is nearly hori- 

 zontal ; and, in proportion as the ventral fins are 

 brought farther and farther forward, the fish in its 

 habit has more occasion to exert itself in raising the 

 head upward when it moves from place to place. In 

 general, too, those fishes which have the ventral fins 

 far backwards, have the body spindle-shaped, and the 

 head not very large ; whereas those which have these 

 fins brought so far forward as to be connected with 



