VERTEBRATA. 299 
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. Destitute of the 
means of social intercourse (being almost mute), their 
chief enjoyment is to eat, and to be eaten is the end of 
their existence. 
But the class yields to no other in the number and varie- 
ty 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 three-fold 
division (as thigh, leg, and foot) found in all other Verte- 
brates.’* 
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 
A 
Fig. 272.Scales of Fishes: A, cycloid scale (Salmon); B, ctenoid scale (Perch); C, 
placoid scale (Ray) ; D, ganoid scales (Amblypterus)—a, upper surface; b, under 
surface, showing articulating processes. 
disproportionately large, but pointed to mect the resist- 
ance of the water. The neck is wanting, the head being 
a prolongation of the trunk. The viscera are closely 
packed near the head, and the long, tapering trunk is left 
