ECONOMIC VALUE OF AMPHIBIANS 
97 
to the first by hibernating in the winter; while the second 
phase of environment may be illustrated as follows: the 
tadpole can live only in water, and if the pond dries up be¬ 
fore the frog stage is reached, the environment has been un¬ 
suited to the tadpole. This often happens when the eggs 
are laid in a temporary roadside pond which evaporates long 
before the tadpole becomes a frog. All such tadpoles die 
unless they are able to 
swim to some other body 
of water. 
The birds that are able 
to fly avoid hibernating in 
the winter. They are able 
to adapt themselves to the 
change in the seasons with¬ 
out burying themselves in 
the mud as the frogs do. 
Some of the birds do 
not migrate, but remain 
all winter in the North. 
They have become so well 
adapted to conditions that 
they are able to get their 
food where birds that mi¬ 
grate would starve. 
Man is the only animal 
that is able to live any¬ 
where on the face of the 
earth under the most varied conditions. To realize this 
fully we have but to think of the different surroundings 
of the Eskimo, Indian, Bushman, and of ourselves. 
Each animal and plant is directly dependent upon its 
environment for food and a home. 
82. Economic Value of Amphibians. — The toad is the 
only member of the amphibian group that is of any great 
Figure 82. —Tree Frog. 
Note the disks at end of toes. Com¬ 
pare the environment of leopard frog 
and tree frog. 
