152 REPORT OF STATE GEOLOGIST. 



Class 2. PISCES. 



THE TRUE FISHES. 



This class contains all our native so-called "fishes," except the 

 lampreys described on the preceding pages. Before proceeding to the 

 classification and description of our fishes it seems proper, for the benefit 

 of those who are beginning their ichthyological studies, to call attention 

 to the structural characters which we must employ, and to define certain 

 terms. 



The body of a fish, a bass, for instance, is recognized as consisting of 

 three portions, head, trunk and tail, the hinder border of the gill-opening 

 and the vent serving as points of division. The head bears the organs of 

 special sense, the beginning of the alimentary canal, together with its 

 weapons of offense and defense, and the organs of respiration. The 

 trunk contains the organs of circulation, of digestion, excretion, and of 

 reproduction. The tail is the principal organ of locomotion. On the 

 body and tail are located the various fins ; some of them occasionally 

 extend even on to the head. 



The brain-case and the skeleton of the tongue and of the gills of some 

 fishes are composed, to a great extent, of cartilage; in others this 

 cartilage is more or less converted into bone ; in all true fishes this 

 cartilage, ossified or not, is covered in by pla'tes of bone laid down in 

 membrane. In and about the mouth are several membrane bones which 

 must receive our attention. Forming the front border of the upper jaw 

 we find two bones, the prema.villaries, which meet in the middle line. 

 Each usually sends backward a process to form the whole or a part of 

 the upper margin of the mouth, and another process upward which lies 

 upon the other bones of the snout. The latter processes move on their 

 bed, so as to aUow the premaxillaries to be pushed forward and with- 

 drawn. However, we do not say that the upper jaw is protractile unless 

 there is a distinct crease of the skin, separating the skin of the upper lip 

 from that of the forehead. The bass and the sun-fishes furnish examples 

 of fishes in which the premaxillaries form the whole of the upper margin 

 of the mouth. In the pike but a small portion of the margin is occupied 

 by the premaxillaries. These bones are likely to bear teeth, in case 

 there are any teeth in the mouth. 



The maxillary usually lies above and behind the premaxillary. It 

 often forms the hinder portion of the margin of the mouth. It is 

 usually flat at the hinder end. It seldom bears teeth, yet it does so 

 in the gars and the mud-fish (Amia). In many fishes, as the bass and 

 pike, there is fouud on the upper border of the max'iUary a, supplementari/ 

 bone. In the fishes of the herring family the maxillary is composed of 

 about three pieces. In the cat-fishes the raaxilliary is a rudiment lodged 



