VERTEBRATA. 
311 
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 all other Vertebrates. 159 
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 
Fig. 283.— Scales of Fishes: A, cycloid scale ( Salmon ); B , ctenoid scale (Perch); C, 
placoid scale (Rxy ); Z>, ganoid scales (Amblypterus)-—a, upper surface; b, under 
surface s showing articulating processes. 
disproportionately large, but pointed to meet the resist¬ 
ance of the w T ater. The neck is wanting, the head be- 
ing a prolongation of the trunk. 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. The biconcave 
vertebrae, with intervening cavities filled with elastic gel¬ 
atin, are designed for rapid and versatile movements. The 
body is either naked, as in the Lamprey, or covered with 
