|S OF FISHES IN GENERAL^ 



Section II. 



Of the external Parts atul Motloti ofFijhes. 



1 HE external form of the greater part of fi(Kes, tendsF 

 greatly to the eafe and celerity of their motion. It is 

 iharp at either end, and fwelling towards the middle ; 

 and is modelled by nature after that ihape, which we en- 

 deavour to imitate in thofe veiTels, that are intended for 

 the greateft defpatch. Every human contrivance, how- 

 ever, falls far fhort of the rapidity of the natives of the: 

 fea. All the larger fifhes can eafily overtake the bell 

 conflru£led veiiel while in full fail ; and play around it, 

 without any apparent effort. 



The principal inllrument of this great velocity in fiHies, 

 is the tail, aided by the flrength and flexibility of the 

 back-bone. The other fins are too fmall, flender, and 

 flexible, compared with the weight of the animal, to im- 

 pel it through the water with fuch vail rapidity and 

 force. Their principal life is to diiefc and moderate the 

 movement, communicated by the impulfe of the tail. 

 A fifh, when deprived of thefe, and put into a pond, 

 darts upwards, downwards, and laterally, with all its 

 wonted velocity, but without being able to dire6t its 

 courfe *. The ventral and dorfal fins, ferve the pur- 

 jjofe of keeping the fifties in an eredl and pei-pendicular 

 pofition ; and, perhaps, the firft contributes to raife or 

 iiok them in the water. The perioral fins regulate and 

 1'affill: progreffive motion. When fwimming rapidly for- 

 ward, 

 * Sa-i'Ji apiid JVill. de nxotu anim. 



