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A HISTORY OF 



The chief instruments in a fish's motion, 

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

 more numerous than in others. A fish com- 

 pletely 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 swift, 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 be- 

 hind the opening of the gills; they are gene- 

 rally large and strong, and answer the same 

 purposes 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 an 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 prone to the 

 bottom, as is seen in large-headed fishes, 

 when the pectoral 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 situation the fish may be ; and 

 they serve rather to raise or depress the fish 

 in its element, than to assist progressive mo- 

 tion. The dorsal fin is situated along the 

 ridge of the back; and serves to keep it in 

 equilibrio, as also to assist its progressive mo- 

 tion. In many fishes this is wanting ; but in 

 all flat fishes it is very large, as the pectoral 

 fins are proportionably small. The anal fin 

 occupies that part of the fish which lies be- 

 tween the anus and the tail ; and this serves 

 to keep the fish in its upright or vertical situa- 

 tion. Lastly, the tail, which in some fishes 

 is flat, and upright in others, seems the grand 

 instrument of motion; the fins are but all 



subservient to it, and give direction to its 

 great impetus, by which the fish seems to dart 

 forward with to 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 dorsal 

 and ventral fins be cut oJF, the fish reels to 

 the right arid 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 off, 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 pectoral fins 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 pectoral fins are small, and 

 the ventral fins totally wanting. 



As most animals that live upon land are 

 furnished with a covering to keep ofT the in- 

 juries of the weather, so all that live in the 

 water are covered with a slimy glutinous 

 matter, that, like a sheath, defends their bo- 



