PISCES. 199 



in the Cephalopoda. The eyes are characterized by their immovable 

 position, flattened cornea, spherical crystalline lens, and brilliant color, as 

 well as by certain internal anatomical peculiarities. The organs of touch 

 lie either in the lips, or in the apparently sensitive barbels or cirri so con- 

 spicuous in some species. 



The teeth are rarely entirely wanting, although sometimes absent from 

 tlie mouth. In this case they are generally to be found in the posterior 

 arch of the gills, when they are called pharyngeal teeth. Such is the case 

 in most of the CyprlnidcB. Some fish have teeth in nearly every bone in 

 the mouth ; on the maxillary, intermaxillary, palatine, vomerine, spheroidal, 

 as well as on the tongue and gill arches. The shape of the teeth, as also their 

 disposition, varies greatly. 



As already remarked, the skin is either naked, or covered with scales ; 

 these occurring in various conditions of development, as true imbricated 

 scales, as isolated scales, as spiny prickles, bristles, hard bony enamelled 

 plates, &c. The side of the fish generally exhibits a longitudinal row of 

 scales, in each of which is a perforation. These holes, constituting by their 

 linear arrangement, the lateral line of the fish, were formerly supposed to 

 secrete mucus. The recent researches of Professor Agassiz have, however, 

 shown that these are the openings of tubes, which, together with similar 

 tubes opening on the skull, penetrate all parts of the body, brain, muscles, 

 bones, and viscera ; freely admitting water, whose hydrostatic action thus 

 equalizes the pressure of the incumbent water, both on the outside and 

 within. 



The colors of fishes are among the most beautiful in nature, being only 

 assimilated, and that in an inferior degree, by those of birds. All shades are 

 represented, as well as all lustres. These hues, however, are very evanes- 

 cent, sometimes departing immediately after death. 



The organs of mice are entirely wanting, and there are but few that are 

 capable of making any sound whatever. The North American cat-fish 

 {Pimelodus) is said to make a peculiar sound by a vibration of its cirri. 

 The weak fish {Otolithus regalis) makes a peculiar grunting when caught, 

 apparently abdominal in its character. The same applies to the black drum 

 (Pogo7iias chroynis). 



While some fish are confined to salt water, and others to fresh, certain 

 species live habitually in a mixture of the two. Others again, at different 

 seasons of the year, occupy both salt and fresh, as the salmon. The distri- 

 bution of species is much affected by the temperature of the water, and the 

 character of the bottom. But few fishes can live out of water for any 

 length of time, owing to the rapid desiccation of the gills, and the conse- 

 quent asphyxia. The eel and the cat-fish (Pimelodus) can exist for sont^ 

 davs in a simply moist or damp situation, as wet grass. Certain species, as 

 the Anabas, habitually leave the water in search of food. 



Fishes are almost incredibly prolific. It has been calculated that the 

 progeny of a single herring, allowed to reproduce and multiply undisturbed 

 for twenty years, would not only supply the whole earth with an abundance 

 of these fish, but would become inconveniently numerous. Yet among 



403 



