41-3 HIS roil V or 



fatigued with its exertions, it is obliged to sink down agaiii. 

 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 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 

 fiat 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 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 pro- 

 portionably 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, 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 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 pec- 

 toral fins, it inclines to the same side ; folding the right pectoral 

 fin, the fish inclines to the right side; folding the left fin, it in- 

 clines to that side in turn. When the fish desires to have a re- 

 trograde motion, striking with the pectoral fins, in a contrary 

 •lirection, eflfectually 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 off, the fish 

 reels to the right and left, and endeavours to supply its loss by 

 keeping the rest of its fins in constant 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 fisii are possess- 



