214 ; NATURAL 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 ofa 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 vertebrated an- 
imals? What is said of the necessity for breathing to a fish? How 
may a fish be drowned? What is the difference 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 their color? 
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