158 NATURAL THEOLOG-r. 



body tlirough a resisting medium, or to maintain the posture, 

 or to support or restore the balance of the body, wliich is 

 always the most unsteady where there is no weight to sink 

 it. For these offices the fins are as large as necessary, 

 though much smaller than wings, their action mechanical, 

 their position and the muscles by which they are moved in 

 the highest degree convenient. The followmg short account 

 of some experiments upon fish, made for the purpose of ascer- 

 taining the use of their fins, will he the best confirmation of 

 what we assert. In most fish, besides the great fin, the tail, 

 w^e find two pairs of fins upon the sides, two single fins upon 

 the back, and one upon the belly, or rather between the 

 belly and the tail. The halancing 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 

 the gills, the head fpJls 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 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 

 observation upon them when put in action. The pectoral, 

 and more particularly the ventral fins, serve to raise and 

 dejoress the fish : when the fish desires to have a retrograde 

 motion, a stroke forward with the pectoral fin eff^ectually 

 produces it ; if the fish desires to turn either way, a f5ingle 

 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 jn-ogressive, and enables the fish to dart for- 

 ward 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 ac- 

 quainted. However, when the tail is cut off', the fish loses 

 all motion, and gives itself up to where the water impels it 

 * Gold>mitli, History of Animated Nature, vol. 6, p. 154. 



