AMPHIBIA 255 



ated with plant food are lost (in frogs they are replaced by 

 bony teeth). 



Tadpoles hatched from eggs laid about the first of June 

 will transform into young toads about the middle of July. 

 As a tadpole nears the end of its sojourn in the water, the 

 gills grow smaller and lungs are developed. Frequent trips 

 are made to the surface of the water and, after the front 

 legs become functional, much time is spent on land, just 

 out of the water. The tail becomes soft and flabby, grows 

 gradually shorter, and finally, some fine day, shrivels up 

 completely. Then the tadpole is no more, but a little toad 

 hops away to hide in the grass and hunt for small insects. 

 Often minute toads migrate from ponds in great armies 

 after a rain, and ignorant people therefore believe that they 

 rained down. The delicate creatures are not yet fully 

 adjusted to life on land and are unusually active when the 

 air is moist. 



If we apply the Law of Biogenesis to the development of 

 a toad, it leads to the same conclusion as in the case of a 

 salamander. The ancestors of amphibians were aquatic 

 fish-like vertebrates which later developed lungs and left 

 the water. Most salientians are more markedly terrestrial 

 than caudate amphibians, and show more striking adapta- 

 tions for life on land. Some species even live in deserts 

 where they pass the dry season in a condition of aestivation, 

 but most amphibians are limited to rather moist situations 

 on account of their soft skins. They are for the most part 

 confined to shady nooks in the shelter of vegetation and 

 seldom hunt in the glare of a noonday sun. They are not 

 as well adapted to the land as reptiles, birds, and mammals. 



GENERAL REMARKS ON SALIENTIANS 



The commonest frogs throughout the United States are 

 the leopard frogs, Rana pipiens, and related species. The 

 green frog, which is often brown or mottled, but may 

 always be recognized by its very large tympanic mem- 



