2U NATUKAL HISTORY. 



361. Fishes surpass any other class of Vertebrates 

 both in actual number and in the number of genera and 

 species. Seven tenths of the earth's surface is covered 

 ■with water, leaving out of view the lakes and rivers. 

 Now in the seas and oceans occupying this immense 

 space Fishes are found, some in shallow waters, some out 

 at sea near the surface, and others at various depths, 

 some even to the depth of several hundred feet. There 

 are different ranges of depth to which different species 

 are fitted. It is among those whose range does not ex- 

 tend much below the surface that we have a display of 

 bright and various colors, equaling, often, that of the 

 Bird and Insect tribes ; while those that frequent the 

 depths are of a dull color. This difference is owing most- 

 ly to the influence of light. At what depth there is a 

 total absence of light, and therefore, probably, of life, has 

 not been ascertained. 



Questions. — How do the Fishes differ from all other veitebrated an- 

 imals? What is said of the necessity for breathing to a fish? How 

 may a fish be drowned ? What is the diiference between lungs and 

 gills ? How are gills constructed and arranged ? Why does a fish die 

 when out of water? Why can some live a considerable time in air? 

 What is the plan of the circulation of fishes ? Why is it best that they 

 should be cold-blooded ? What is said of the shape of a fish ? Why 

 has it no neck ? What is said of its covering ? How is the motion 

 of fishes contrasted with that of birds?' What is said of the Flying 

 Fish ? How do fishes use their air-bladder ? What is said of the use 

 of the tail and of the fins in swimming ? What is said of the skele- 

 tons of fishes ? How is the Fish adapted in its nervous system and its 

 senses to its mode of life ? What organs of touch do we see in some 

 fishes ? What is said of the organs of vision in fishes ? What of their 

 sense of smell? What is said of their food ? Give the statement of 

 Dr. Houston. What is said of the mouths of fishes ? How do fishes 

 compare with other vertebrates in number and variety? What is 

 said of the various depths in which they live ? What influence has 

 this on tbeir color? 



