BIONOAIIC CHARACTERS OF AMPHIBIA 1035 



Red Sandstone, the Devonic sandstones of Canada, the Coal Mea- 

 sures and the continental Permic deposits. The living Protopterus 

 of Africa regularly spends the dry season of several months in its 

 crust of dried mud. leading a latent existence or summer sleep until 

 the rains again soften the crust and release the fish. 



The various species of mud-fish are examples of fishes leading 

 an amphibious life, for these have been transported in their "nest" 

 of dried mud halfway round the world without suffering. Dean 

 believes that the vitality of these fish becomes exhausted by being 

 kept in water all the time, which deprives them of their periodic 

 summer rest. Many fresh-water fisli regularly swallow air and 

 will die if prevented from doing so, even more quickly than frogs 

 which have been similarly placed, although the latter are provided 

 with true lungs. 



A few other types of fish are able to live in the air for a certain 

 length of time, as, for example, the tropical fish (Periophthalmus 

 and Boleophthalmus). referred to in the preceding chapter, which 

 spend a good part of their existence on the beach, and Anabas 

 scandens of the Philippines is able to exist for days out of water. 



Many fresh-water fish periodically visit the sea, while marine 

 fishes as frequently ascend fresh-water streams. 



Amphibia. The amjihibians are cold-blooded, aquatic or ter- 

 restrial vertebrates, usually without dermal covering, which, how- 

 ever, is present in some forms as a corneous or osseous structure. 

 These animals breathe by gills and by lungs, the former remain- 

 ing functional throughout life in some species. True limbs are 

 generally present in the Amphibia, and are used for swimming or 

 walking. 



The Carbonic and Triassic Stegocephalia were mostly ar- 

 mored, especially on the ventral side. They lived on land or 

 possibly in fresh water. The larger forms were predatory and 

 probably fed on other amphibians, fishes, and Crustacea. Tlie 

 CcEcilians (Gymnophiona ) are worm-like, legless amphibians con- 

 fined to the tropics. They are unknown in the fossil state. The 

 Urodeles are naked-bodied types with generally two j^airs of limbs 

 and persistent tail. They inhabit fresh water (newts), where the 

 gills remain permanent; or ^^lamp. shady places on the land (sala- 

 manders), where they lose their gills. They subsist on worms, 

 gastropods, small aquatic animals, anfl fish spawn. Permanent 

 larval forms (Axolotl) of the land form, Amblystoma, inhabit 

 the lakes and ponds of Mexico and other countries. These have 

 the form of large tadpoles about to be transformed, with legs and 

 external gills. They reproduce in this state, some of them never 



