24-2 



HISTORY OF FISHES. 



Most fish offer us the same external form ; 

 sharp at either end, and swelling in the mid- 

 dle; by which they are enabled to traverse the 

 fluid which they inhabit, with greater celerity 

 and ease. That peculiar shape which Nature 

 has granted to most fishes, we endeavour to 

 imitate in such vessels as are designed to sail 

 with the greatest swiftness : however, the pro- 

 gress of a machine moved forward in the water 

 by human contrivance, is nothing to the ra- 

 pidity of an animal destined by nature to re- 

 side there. Any of the large fish overtake a 

 ship in full sail with great ease, play round it 

 without effort, and outstrip it at pleasure. 

 Every part of the body seems exerted in this 

 despatch ; the fins, the tail, and the motion 

 of the whole back-bone, assist progression ; and 

 it is to that flexibility of body at which art 

 cannot arrive, that fishes owe their great velo- 

 city. 



The chief instrument in a fish's motion, are 

 the fins, which, in some fish, are much more 

 numerous than in others. A fish completely 

 fitted for sailing, is furnished with not less 

 than two pair ; also three single fins, two above 

 and one below. Thus equipped, it migrates 

 with the utmost rapidity, and takes voyages 

 of a thousand leagues in a season. But it 

 does not always happen that such fish as have 

 the greatest number of fins have the swiftest 

 motion ; the shark is thought to be one of the 

 swiftest swimmers, yet it wants the ventral or 

 belly fins; the haddock does not move so swiit, 

 yet it is completely fitted for motion. 



But the fins serve not only to assist the ani- 

 mal in progression, but in rising or sinking, 

 in turning, or even leaping out of the water. 

 To answer these purposes, the pectoral fins 

 serve, like oars, to push the animal forward ; 

 they are placed at some little distance behind 

 the opening of the gills ; they are generally 

 large and strong, and answer the same pur- 

 poses to the fish in the water, as wings do to 

 a bird in the air. With the help of these, and 

 by their continued motion, the flying fish is 

 sometimes seen to rise out of the water, and 

 to fly above a hundred yards ; till, fatigued 

 with its exertions, it is obliged to sink down 

 again. These also serve to balance the fish's 

 head, when it is too large for the body, and 

 keep it from tumbling down to the bottom, as 

 is seen in large-headed fishes, when the pec- 

 toral fins are cut off. Next these are seen the 

 ventral fins, placed towards the lower part of 

 the body, under the belly ; these are always 

 seen to lie flat on the water, in whatever situ- 

 ation the fish may be; and they serve rather 

 to raise or depress the fish in its element, than 

 to assist progressive motion. The dorsal fin 

 is situated along the ridge of the back ; and 

 serves to keep it in equilibrio, as also to assist 

 its progressive motion. In many fishes this 



is wanting ; but in all flat fishes it is very 

 large, as the pectoral fins are proportionabiy 

 small. The anal fin occupies that part of the 

 fish which lies between the anus and the tail; 

 and this serves to keep the fish in its upright 

 or vertical situation. Lastly, the tail, which 

 in some fishes is flat, and upright in others, 

 seerns the grand instrument of motion ; the 

 fins are but all subservient to it, and give di- 

 rection to its great impetus, by which the fish 

 seems to dart forward with so much velocity. 

 To explain all this by experiment ; a carp is 

 taken, and put into a large vessel. The fish, 

 in a state of repose, spreads all its fins, and 

 seems to rest upon its pectoral and ventral fins 

 near the bottom ; if the fish folds up (for it has 

 the power of folding) either of its pectoral fins, 

 it inclines to the same side ; folding the right 

 pectoral fin, the fish inclines to the right side ; 

 folding the left fin, it inclines to that side in 

 turn. When the fish desires to have a retro- 

 grade motion, striking with the pectoral fins, 

 in a contrary direction, effectually produces 

 it. If the fish desires to turn, a blow from 

 the tail sends it about ; but if the tail strikes 

 both ways, then the motion is progressive. 

 In pursuance of these observations, if the dor- 

 sal and ventral fins be cut off, the fish reels to 

 the right and left, and endeavours to supply 

 its loss by keeping the rest of its fins in con- 

 stant employment. If the right pectoral fin 

 be cut oil', the fish leans to that side ; if the 

 ventral fin on the same side be cut away, then 

 it loses its equilibrium entirely. When the 

 tail is cut off, the fish loses all motion, and 

 gives itself up to where the water impels it. 



From hence it appears, that each of these 

 instruments has a peculiar use assigned it; 

 but, at the same time, that they all conspire 

 to assist each other's motions. Some fish are 

 possessed of all, whose motions are yet not 

 the swiftest ; others have but a part, and yet 

 dart in the water with great rapidity. The 

 number, the size, and the situation of the fins, 

 therefore, seem rather calculated to correspond 

 with the animal's figure, than solely to answer 

 the purposes of promoting its speed. Where 

 the head is large and heavy, there the pec- 

 toral tins are large, and placed forward, to 

 keep it from oversetting. Where the head is 

 small, or produced out into a long beak, and 

 therefore not too heavy for the tail, the pec- 

 toral fins are small, and the ventral fins totally 

 wanting. 



As most animals that live upon land are 

 furnished with a covering to keep off the in- 

 juries of the weather, so all that live in the 

 water are covered with a slimy glutinous mat- 

 ter, that, like a sheath, defends their bodies 

 from the immediate contact of the surrounding 

 fluid. This substance may be considered as a 

 secretion from the pores of the animal's body : 



