NATURAL THEOLOGY. 245 



the fish leans to that side ; if the ventral fin on 

 the same side be cut away, then it looses its equi- 

 librium entirely ; if the dorsal and ventral fins be 

 cut off, the fish reels to the right and left. When 

 the fish dies, that is, when the fins cease to play, 

 the belly turns upwards. The use of the same 

 parts for motion is seen in the following ob- 

 servation upon them when put in action. The 

 pectoral, and more particularly the ventral fins, 

 serve to i^aise and depress the fish ; when the fish 

 desires to have a retrograde motion, a stroke for- 

 w^ard with the pectoral fin effectually produces it ; 

 if the fish desire to turn either way, a single blow 

 with the tail the opposite way sends it round at 

 once ; if the tail strike both ways, the motion pro- 

 duced by the double lash is progressive, and en- 

 ables the fish to dart forward with an astonishing 

 velocity.* The result is, not only in some cases 

 the most rapid, but in all cases the most gentle, 

 pliant, easy, animal motion with which we are 

 acquainted. However, when the tail is cut off, 

 the fish loses all motion, and gives itself up to 

 where the water impels it. The rest of the fins, 

 therefore, so far as respects motion, seem to be 

 merely subsidiary to this. In their mechanical 

 use, the anal fin may be reckoned the keel ; the 

 ventral fins, out-riggers ; the pectoral muscles, the 

 oars , and if there be any similitude between these 

 parts of a boat and a fish, observe, that it is not 



* Goldsmith, Hist, of An. Nat. vol. vi. p. 154, 

 21* 



