FISHES CONSIDERED AS A CLASS. 251 



is chiefly by the Lateral motions of the tail and body that 

 Fishes are propelled; although some Fishes as Pipe- 

 fishes (Fig. 311) swim principally by the undulation of 

 the dorsal fin. The fins are employed mainly in balancing 

 and directing. 



The muscular system is generally highly developed. 

 The flesh, excepting certain muscles which are deep red, 

 is paler than that of Birds and Mammals, and in some cases 

 is pure white. One large and complicated muscle on each 

 side, and filling up the space from the head to the tail, fur- 

 nishes the principal motive power. 



The brain is exceedingly small, and seldom fills the 

 cavity in which it is situated (Fig. 292). 



With few exceptions, the eye of Fishes has no motion ; 

 arid the iris neither contracts nor dilates, and the pupil is 

 not altered, whatever be the quantity of light. 



The ear of Fishes is inclosed on every side in the bones 

 of the head, and consists merely of a sac, representing the 

 vestibule, and of three membranous semicircular canals. 

 In the former are suspended small hard bodies. 



The sense of taste, of smell, and of touch, are regarded 

 as feeble ; although, in relation to taste, it should be stated 

 that some fishes show a decided preference for one kind 

 of bait over another, not only in taking it, but in cling- 

 ing to it. 



Most fishes are oviparous in their manner of reproduc- 

 tion ; but some species bring forth living young. They 

 produce a far greater number of eggs than any other 

 vertebrates. A Salmon sometimes contains as many as 

 20,000 eggs; a Perch, 28,000; a Herring, 36,000; a 

 Mackerel, 546,000 ; a Flounder, 1,357,000 ; a Sturgeon, 

 7,600,000; a Cod, 9,000,000; and a species of Upeneus, 

 13,000,000! 



