92 
AMPHIBIANS 
As soon as the young tadpole hatches, it attaches itself 
to plants and lives for the first few days upon the food- 
yolk within its own body; the mouth forms, and horny 
jaws develop. Then the tadpole begins to feed upon minute 
plants and becomes dependent upon its own skill to get food 
and escape its enemies. 
For a time the tadpole breathes through gills. Two sets 
are used. The first ones are on the outside of the body and 
last for only two or three days, when internal gills form in the 
throat and the tadpole breathes much like a fish. 
Figure 78.— The Embryo Becoming a Tadpole. 
The Tadpole Becomes a Frog. — In the growth of the 
tadpole into a frog the hind legs appear first. Later the 
front ones begin to show and as they develop the tail is grad¬ 
ually absorbed. While these external changes are going on, 
there are many complicated internal changes taking place; 
internal gills are disappearing and lungs, nerves, blood ves¬ 
sels, and muscles are being formed to give the new legs life 
and action. The internal lungs take the place of the gills 
in the throat before the legs are fully grown and such tadpoles 
must rise to the surface to breathe air. Explain in Figure 
79 which tadpoles breathe by lungs, and which by gills. 
This complicated way of growing into a frog is called meta¬ 
morphosis and this term has the same general meaning as 
when used to describe the growth of insects (page 26). 
The tadpoles of leopard frogs become small frogs in a 
