FINS 77 



which is supported by the fin-rays is visible without dissection. 

 These rays may be simple or branched, and in some of the 

 Cat-fishes there is a stout spine along the outer edge of the 

 fin, which may be saw-edged along one or both of its margins 

 and attached to the body by an elaborate joint (Figs. 29A; 

 34k). In the Mad Toms or Stone Cats [Noturus, Schilbeodes) of 

 the United States, each of the spines is provided with a special 

 poison gland at the base. A South American Cat-fish {Doras) 

 uses the spines of the pectorals for progression overland, pro- 

 jecting itself along on the tips by the elastic spring of the 

 tail (Fig. 34k). ^ , . i7- u 



The shape of the pectorals also varies to some extent. Irishes 

 of moderate or slov/ speed, which may use these fins for pro- 

 pulsion or for backing water, have broad, rounded or spatulate 

 pectorals (Fig. 34e). In speedy fishes, on the other hand, where 

 they are employed in executing wheeUng or turning move- 

 ments, the fins are always longer and frequently sickle-shaped 

 (falcate) (Fig. 34c). The pecuhar leaf-like paired fins of the 

 Australian Lung-fish {Epiceratodiis) have been described on an 

 earher page (Fig. 99c). In the other Lung-fishes from Africa 

 [Protopterus) and South America (Lepidosiren) the central lobe 

 becomes long and narrow, the marginal fringe is reduced or 

 entirely suppressed, and the fins take the form of long, tapermg 

 filaments (Fig. 99A, b). Rarely are the pectoral fins wanting, 

 although they may be much reduced in size and efficiency. In 

 some of the Pipe-fishes, however, and in certain of the Eels, 

 they are absent. 



The pectoral fins, therefore, are concerned mainly with 

 propulsion or steering. The older authors laid considerable 

 stress on their use as organs of balance, but more recent experi- 

 ments tend to show that neither of the paired fins plays any 

 important part in the maintenance of equilibrium. A number 

 of fishes have been experimented upon by removing some or 

 all of these fins, and in no case was the horizontal position 

 seriously affected, provided the individuals remained at rest 

 and attempted no turning movements. True, sick or dead 

 fishes generally float belly upwards, but this is probably due 

 to physiological causes. As in the case of the dorsal and anal, 

 the pectorals have become variously modified in certain fishes 

 for the performance of new functions, and the more interesting 

 of these adaptations may now be examined. 



The Flying-fishes [Exocoetidae) have greatly enlarged pec- 

 torals, often extending backwards as far as the tail (Fig. 34J), 



