STRUCTURE OF FISHES. 83 



18. In a small number of fishes, the pectoral fins are so very 

 much developed, as to enable the animal to sustain itself in the 

 air for a few moments, when it springs out of water. There are 

 some also, that by crawling, or by frequent leaps, are capable of 

 progression on land. It is asserted that some can climb trees ; 

 but instances of this kind, are very rare. 



19. Fishes pass their lives almost entirely in providing for 

 their subsistence, or in escaping from their enemies ; their ex- 

 ternal senses seem to afford them only very du41 impressions, and 

 their faculties are of the most limited character. 



20. Fishes are very stupid animals ; they have no remarkable 

 intelligence or instinct, and their brain, (Fig. 45, t.) is but little 

 developed ; it does not entirely fill the cavity of the cranium, and 

 is surrounded by a liquid matter of a fatty nature. 



21. The ear of fishes, in general, is composed only of a vesti- 

 bule, surmounted by three membranous semi-circular canals, 

 suspended in the cavity of the cranium, on each side of the brain, 

 and to which waves of sound are communicated, only after they, 

 have set in vibration the common integuments and bones of the 

 cranium Generally, there is no appearance of an external ear. 

 Their eyes are ordinarily very large, and are unprovided with 

 true eye lids, and a lachrymal apparatus ; the skin which covers 

 them is transparent ; and the iris is silvery and immoveable, or 

 nearly so, and the cornea is almost flat, the pupil is very large, 

 and the chrystalline lens is spherical. The nasal fossae do not 

 open into the pharynx, as is the case in vertebrate animals that 

 breathe air. The tongue is never truly fleshy, and the sense of 

 taste is but little developed. Tact must be extremely obtuse. 

 In general, the skin of these animals is entirely covered with 

 scales ; sometimes, however, it is naked. 



22. Ordinarily fishes are very voracious, and are not very 

 particular in their choice of food. The species which live chiefly 

 on vegetables, are very few in number; they are almost all 

 carnivorous, and devour each other. 



23. Fishes sometimes have teeth, not only in the jaws, but also 

 in all the bones that surround the cavity of the mouth, and that 

 of the pharynx ; at other times they are entirely wanting. These 

 teeth never have roots, and their form varies very much, parttcu- 



18. Are fishes capable of progression, when out of water ? 



19. Are the senses of fishes very acute? 



20. What is the character of the brain in fishes ? 



21. What is the character of the ear in fishes ? What are the peculiari- 

 ties of the eye ? What are the peculiarities of the nasal fossae ? 



22. Upon what do fishes generally feed ? 



23. What is the character of the teeth of fishes ? 



