122 



AMPHIBIANS 



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. 



121. The Tadpole Be- 

 comes 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 

 gradually absorbed. While these external changes are 

 going on, there are many complicated internal changes 

 taking place ; internal gills are disappearing and lungs, 

 nerves, blood vessels, and muscles are being formed to give 



Figure 120. — Dividing Egg of Frog. 



Figure 121. — Dividing Egg Becoming a Tadpole. 



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 can breathe only air. Ex- 

 plain in Figure 122 which tadpoles breathe by lungs 



