VERTEBRATA 145 



teeth, one nasal organ, no scales, limbs, or gill arches. 

 The gills are in pouches which open separately. They 

 are found both in salt water and in fresh water. 



CLASS II. Pisces 



Fishes fall far behind the rest of the typical craniates 

 in strength, intelligence, and sensibility. The eyes, 

 though large, are almost immovable, bathed by no tears, 

 and protected by no lids. Dwelling in the realm of 

 silence, ears are little needed, and such as they have are 

 without external parts, the sound being obliged to pass 

 through the cranium. Taste and smell are blunted, and 

 touch is nearly confined to the lips. 



The class yields to no other in the number and variety 

 of its forms. It includes nearly one half of all the ver- 

 tebrated species. So great is the range of variation, it 

 is difficult to frame a definition which will characterize 

 all the finny tribes. It may be said, however, that fishes 

 are the only backboned animals having median fins (as 

 dorsal and anal) supported by fin rays, and whose limbs 

 (pectoral and ventral fins) do not exhibit that threefold 

 division (as thigh, leg, and foot) found in most other 

 craniates. 



The form of fishes is admirably adapted to the element 

 in which they live and move. Indeed, Nature nowhere 

 presents in one class such elegance of proportions with 

 such variety of form and beauty of color. The head is 

 disproportionately large, but pointed to meet the resist- 

 ance of the water. The neck is wanting, the head be- 

 ing a prolongation of the trunk (Fig. 320). The viscera 

 are closely packed near the head, and the long, tapering 

 trunk is left free for the development of muscles which 

 are to move the tail the instrument of locomotion 

 (Fig. 321). The biconcave vertebrae, with intervening 

 DODGE'S GEN. ZOOL. 10 



