184 



SUBKIKGDOM VERTEBRATA. 



CLASS V. PISCES. 



General Characteristics. Fishes rank lowest among 

 vertebrates. Their bodies occupy a horizontal position, with 

 Fig S13f no power even of elevating 



the head independently. 

 Their senses are blunted. 

 Their eyes are large, but 

 generally have no motion. 

 The external ears are want- 

 ing. They progress mainly 

 by horizontal movements of 

 the vertical tail, in marked 

 contrast with the vertical 

 movements of the horizon- 

 tal tail of the mammals in- 

 habiting the water. The 

 two pairs of fins underneath,, 

 corresponding to the four 

 limbs of quadrupeds, as well 

 as the fins upon the back, 

 serve as balancers. Most 

 fishes have a swimming-blad- 

 der a sort of rudimentary 

 lung whose use is doubt- 

 ful, though it is thought to 

 be serviceable in changing 

 their specific gravity. They 

 breathe by means of gills. 

 These are delicate fringes or 

 _ SYSTEM or Fisn.-a. Bran- laminae on each side of the 



chial artery: b. Arterial bulb; c. Van- head, generally protected by 

 tticte of heart; d. Auricle; . FOW i ^ ,, , ,, . 



sinus; I. Vena forte, esc. ; g. Intestine; a l onv tne ff*** 



h. Vena cam ; i. GUI teasels : k. Urn sal COVBT. TllO Water, Usually 

 1. Kidneys; m. Aorta. 



way similar to the act of swallowing, bathes the gills, and is then 



