TELEOLOGY OF THE SKELETON OF FISHES. 157 



fins upon the sides, two single fins upon the back, and one upon the 

 belly, or rather between the belly and the tail. The balancing use of 

 these organs is proved in this manner. Of the large-headed fish, if 

 you cut off the pectoral fins, that is the pair which lies close behind 

 tlie gills, the head falls prone to the bottom ; if the right pectoral fin 

 only 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 ; if the 

 dorsal and anal 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 follow- 

 ing observation upon them when put into action. 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 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 produced by 

 the double lash is progressive, and enables the fish to dart forwards 

 Avith 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. Plowever, Avhen the tail is 

 cut off, the fish loses all motion, and it gives itself up to Avhere the 

 w^ater 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 outriggers ; 

 the pectoral fins the oars ; and if there be any similitude between 

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

 of imitation, but the likeness which arises from applying similar 

 mechanical means to the same purpose." (xli. p. 257.) * 



* See also Carlisle I'liil. Trans. 1806, p. 3. 



