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 210, 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 



