ACTIOX OF THE FINS IN FISHES. 6^ 



to tlie right and left ; when the caudal fin is cut ofi* the 

 fish loses the power of progressive motion ; when the fish 

 dies, and the fins cease to play, the belly turns upwards. 

 Paley thus sums up the actions of the fins of fishes : 

 "The pectoral, and more particularly the ventral, fins 

 serve to raise and depress the fish ; when the fish desires 

 to have a retrograde motion, a stroke forward with the 

 pectoral fin efiectually 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 produced by the double lash is progressive, 

 and enables the fish to dart forwards with an astonishing 

 velocity. The result is not only in some cases the most 

 rapid, but in all cases the most gentle, pliant, easy ani- 

 mal motion with which we are acquainted." " In their 

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

 the ventral fins, the outriggers; the pectoral fins, the 

 oars ;" and we may now add " the caudal fin, the screw- 

 propeller." And if there be such similitude between 

 those parts of a boat and a fish, " observe," adds Paley, 

 "that it is not the resemblance of imitation, but the like- 

 ness which arises from applying similar mechanical means 

 to the same purposes."^ 



» "Nat. Theology," 8vo., 1805, p. 257. 



