FINS: THEIR USES. 63 



astern, to check further forward movement, or to 

 move actually backwards. The chief use of the 

 pectoral fins is to serve as steering agents. When 

 the fish wants to turn to the right, for instance, 

 he gives a sudden turn of the tail to the left, 

 the left pectoral fin acting at the same time, 

 whilst the right remains closely pressed against 

 the body. But the chief function of the paired 

 fins is that of balancers. Thus, when the pectoral, 

 or pectoral and pelvic of one side are removed, 

 the fish at once loses its balance and falls over to 

 the opposite side ; if both pectoral fins are lost, 

 it seems the fish's head sinks ; if the dorsal and 

 anal fins are lost, the course of the fish at once 

 becomes very erratic. The loss of all the fins 

 causes the fish to float belly upwards, like a dead 

 fish. 



The forms which the fins take are very varied. 

 Let us begin our study of the variation of the 

 fins with the pectorals. These, by an enormous 

 increase in size, may serve as parachutes, en- 

 abling the fish to take long parachute-like flights 

 through the air as in the "flying herrings' 7 and 

 41 flying-gurnards." Or some of the rays may be 

 modified to form finger-like organs for creeping 

 along the sea-floor as in the gurnards ; or some, 

 or all of the rays, may be enormously elongated to 

 form delicate organs of touch. Thus in Pentamerus 

 from the West Coast of Africa, and West Indies, 

 some five of the pectoral rays may be produced 

 into long hair-like filaments much longer than 

 the body. The South American cat-fish (Doras) 

 goes to the other extreme, and has the pectoral 

 modified into a sharp spine. In one of the 



