150 NATURE-STUDY 



the skin is used partly as an organ of respiration. As a 

 rule, these animals do not have claws on their toes. 



But it is their development from the egg that especially 

 differentiates amphibians from the reptiles. The eggs are 

 generally laid in the water, or in some moist place, where 



FIG. 31. Strings of Toad's Eggs. 



they hatch from natural heat, not into frog-like or salamander- 

 like forms, but into tadpoles. 



Tadpoles at first have no visible gills, but very soon there 

 develop on each side of the head or neck branching gills. 

 Later these disappear, inside gills develop, and gill slits 

 are left in the neck as in fishes. In fact, the tadpole stage 

 corresponds very closely in its structure and physiology to 

 the fish. During this time the tadpole lives an aquatic life 



