CHAPTER XX. 
THE DISTRIBUTION OF ANIMALS. 
Distribution in Land, Water, and Air. We have 
already discovered that we must look in different places 
to find different animals. We should not think of 
searching for bees in a desert, nor for cockroaches in 
the fields along with grasshoppers and crickets. We 
have learned that the larvae of dragon-flies and mos¬ 
quitoes live in the water, while the full-grown insects 
inhabit the air. We do not expect to find caterpillars 
either swimming or flying. The place in which an 
animal lives is called its habitat. Animals living 
mostly in the air are said to be aerial , those inhabiting 
the dry land terrestrial , and those dwelling in the 
water aquatic. Aquatic animals may be either fresh¬ 
water or marine forms. 
Distribution in Altitude. In either of the above 
cases the distribution seems to be influenced by alti¬ 
tude, or, as we speak of it in the case of aquatic animals, 
by depth. One species of butterfly is found only on 
the summits of the White Mountains in New Hampshire; 
others are always seen flying near the ground in the 
valleys, while still others live in mid-air. Among 
marine animals this dependence on altitude is very 
marked. If the piles of a wharf be examined at low 
tide we find the animal life marked off into distinct 
zones parallel with the various levels of the water. 
Distribution Over the EartlPs Surface. We are 
familiar with the fact that certain animals are charac¬ 
teristic residents of definite portions of the world. 
Animals belonging exclusively to arctic, temperate, or 
236 
