AMPHIBIANS. 
37 
the reptiles, however, in having cold blood and a 
three-chambered heart. Their skin is mostly soft, 
cool, and moist. 
2. “We put toads and salamanders in the same 
class with frogs, and call them all Amphibians, 
because they live both in water and on land. 
“ At first they have gills, and can only breathe 
the air that is in water, as fishes do. In time 
Different Stages in the Development of Tadpoles into Frogs. 
lungs grow, and then the gills generally disappear, 
and the animal mostly gives up its life in the water 
for a life on land. 
3. “ So, as I told you, they differ in a very strik- 
ing way from reptiles, for those creatures never 
have gills, but always breathe by means of lungs.” 
“ Yet turtles and crocodiles, which are reptiles, 
live in the water,” said William. 
“ True,” said Mr. Johnson, “ but in breathing 
they are obliged to put their nostrils above the 
surface to obtain air.” 
