82 



THAT S IT ; 



means of fins, 5, and tails, 6 ; 



most of them are covered with 

 cartilaginous scales, 

 9 ; while a few have #J! 

 a complete covering 

 of horny plates, 358. 

 The elongated oval 

 form of their bodies 

 facilitates their motion in water. 

 Many of them are provided with 

 air-bladders, 8 ; by increasing or re- 

 ducing the amount of air 

 in these, they facilitate 

 their rising or sinking in 

 the water. The Jins con- 

 sist of a thin elastic mem- 

 brane, supported by bony 

 rays, and are named, from 

 their position on the body, 

 the pectoral, 10, ventral, 

 11, anal, 12, dorsal (some- 

 339 - times consisting of one long 

 fin, otherwise divided into two), 

 13, 14*. The caudal fin, 15, is 

 more commonly called the tail. 



3i0. 



The use of fins is not alone to promote the 

 motion of fish : they are also, used, in certain 

 circumstances, as instruments of touch. Pro- 

 fessor Owen says : — " You may notice the tac- 

 tile action of the pectoral fins, 10, when gold 

 fiaJi are transferred to a strange vessel : their 

 eyes are so placed as to prevent their seeing 



* Called the first dorsal Vi, and second dorsal, U, 

 when so divided. 



what is below them ; so that they c'Ompresa 

 their air-bladder, 8, and allow themselves to 

 sink near the bottom, which they sweep, as it 

 were, by rapid and delicate vibrations of the 

 pectoral fins, apparently ascertaining that no 

 sharp ston£ or stick projects upwards, which 

 might injure them in their rapid movements 

 around their prison." 



The tails of fishes, 15, have cer- 

 tain distinctions of form, adapted 

 to the uses of the different tribes : 

 there is the simple tail of the 

 eel, 16, the expanded tail of the 



341. 



salmon, 18, the rounded tail of 

 the wrasse, 17, the unequally 

 bilobate # tail of the shark, 19. 

 Tails are their principal organs 

 of locomotion : they skull them- 

 selves along by rapid strokes from 

 side to side. The fins assist their 

 motions principally by balancing 

 the body, and guiding it as it 

 moves along. 



The sight of fishes is quick and 

 accurate. 

 They have no 

 eyelids, be- 

 cause the wa- 

 ter in which 

 they swim at 

 once cleanses 

 and moistens 

 the surface of 342. 

 their eyes, which are generally 

 large, 20, and placed in that posi- 



• Divided into two* 



