INTRODUCTION. XXI 



represents one half of this pharyngeal arch of bone, that of 

 the left side, looking from behind, with the teeth in the 

 Carp, Tench, the Roach, and the Barbel. In the Carp, 

 the first on the left hand, the crowns of the teeth are ob- 

 served to be so worn down as to have the appearance of the 

 crowns of the molar teeth in the hare. In the Tench, the 

 second figure from the left, the structure is less complicated. 

 In the Roach, the form and number again vary; and in 

 the Barbel, on the extreme right, the teeth are crooked, 

 pointed, and disposed in three regular rows : other fishes 

 belonging to this family have the teeth in four rows, and 

 some in six rows. Considerable difference of form exists in 

 the four examples of teeth here shown ; and a reference to the 

 illustrations of other teeth at pages 112, 119, 122, 126, 

 129 132, and 278 in volume i. and those of the Sharks near 

 the end of volume ii. will show the great variety of teeth that 

 are to be found among fishes, two or more distinct forms of 

 which are sometimes possessed by the same individual. Some 

 further particulars in reference to the teeth will be found 

 in other parts of this work. 



Closely connected with this part of the subject is their 

 food, and the organs of digestion. 



The food of fishes is very different at different periods of 

 the year, and this may be one of the causes, among others, of 

 the peculiar excellence of the flesh of some species of fishes at 

 particular seasons. 



The parietes of the stomach in fishes are thin ; and as the 

 food of a very large proportion of them is of an animal na- 

 ture, their digestion is rapid and their intestines short. In 

 some fishes that feed almost entirely on small testaceous 

 animals, which they swallow whole, the walls of the stomach 

 are thickened, affording increased muscular power, as in the 

 Gillaroo Trout, which has been compared to the gizzard of a 

 bird. The most gizzard-like stomach among fishes that I 



