CLASSIFICATION OF AMPHIBIA. 



557 



in Brazil and Mexico ; Epicrium in Ceylon ; Rhinatrema in Cayenne ; 

 C cecilia compressicauda is viviparous. 



Order LABYRINTHODONTIA or STEGOCEPIIALA. 



Extinct forms, occurring from Carboniferous to Triassic strata. 

 Dermal armour is present, the teeth are frequently folded in a com- 

 plex manner. Mastodonsaurus, Dendrerpeton, Archegosaurus. 



Life of Amphibians. 



Most Amphibians live in or near fresh water ponds, swamps, and 

 marshes. Even those adults which have lost all trace of gills are usually 

 fond of water. The tree-toads, such as Hyla> are usually arboreal in 

 habit, while the Gymnophiona and some toads are subterranean. 



The black Salamander (Salamandra atra] of the Alps lives where 

 pools of water are scarce, and instead of bringing forth gilled young, as 

 its relative the spotted salamander (S. maculosa) does, bears them as 

 lung-breathers, and only a pair at a time. But if the unborn young are 



removed from the body of the 

 mother and placed in water, they 

 form gills like other tadpoles. 

 Within the mother, the respira- 

 tion and nutrition of the young 

 seems to be effected by crowds 

 of red blood corpuscles which 

 are discharged from the walls of 

 the uterus. 



Species of Hylodes, such as 

 H. martinicensis of the West 

 Indian Islands, live in regions 

 where there are few pools. In 

 such cases the development is 

 completed within the egg-case, 

 FIG. 189. Ccecilian (Icthyophis) and a lung-breathing tailed larva 

 with eggs. (After SARASIN.) is hatched in about fourteen 



days. It is likely that the tail 



helps in respiration before hatching, but one observer reports the 

 presence of small gills. 



In some Mexican and N. American lakes, there is an interesting 

 amphibian known as Amblystoma or Siredon. It has two forms, one 

 losing its gills (Amblystoma), the other retaining them (Axolotl}. Both 

 these forms reproduce, and both may occur in the same lake. Formerly 

 they were referred to different genera. But the fact that some Axolotls, 

 kept in the Jardin des Plantes in Paris, lost their gills when their 

 surroundings were allowed to become less moist than usual, led 

 naturalists to recognise that the two forms were but different phases of 

 one species. It has been shown repeatedly, that a gilled Axolotl may 

 be transformed into a form without gills, and this metamorphosis seems 

 to occur constantly in one of the Rocky Mountain lakes. The facts do 

 not, however, justify the hasty conclusion that the change from the 

 gilled to the gill-less form is determined only by differences in amount 



