GENERAL OUTLINES OF ICHTHYOLOGY. 11 



Two better examples of these laws could not perhaps be 

 given than those of the Bleak, a surface-swimmer, and the 

 Tench, a ground-swimmer. Amongst sea-fish, Mackerels, 

 Salmon, and Herrings may be quoted as instances of the 

 former law, and Eels, Flat-fish, and Skate of its converse. 



Fish are sometimes designated " surface-swimmers," 

 " midwater-swimmers," or " ground-swimmers," accord- 

 ing to the part of the water which they naturally inhabit. 



With a low standard of respiration, and tenacity of life, 

 is connected the extraordinary power exhibited by some 

 species of sustaining extremes of high and low tempera- 

 ture. The Gold-fish lives and thrives in water as high as 

 85° Fahr. Fishes exist in the hot springs and baths of 

 various countries, ranging from 113° to 120°; and in 

 South America Humboldt saw fish thrown up alive, and 

 apparently in health, from the bottom of a volcano, along 

 with water and heated vapour which raised the thermo- 

 meter to 310°, or two degrees below the boiling-point. 



On the other hand, in parts of Europe and North Ame- 

 rica, Perch and Eels, and several species of Carp, are not 

 uncommonly frozen and thawed again, and even trans- 

 ported from place to place in a frozen state, without injury 

 to life. 



Sight. 



The eyes of fish occupy entirely different positions in 

 the different species, — in some, such as the Skate, being 

 placed high up, near the top of the head, and in others, as 

 the Pike, lower down on the side of the head (the more 



