LIFE OF AMPHIBIANS. 557 



Order Gymnophiona or Apoda. 



Worm-like or snake-like forms, subterranean in habit ; without limbs 

 or girdles ; with extremely short tail ; with dennic scales concealed in 

 the skin ; in at least some forms, gills occur in early life ; the eyes are 

 rudimentary; peculiar "tentacles" are connected with the orbit, and 

 are perhaps equivalent to the "balancers" which occur in some larval 

 Urodela in front of the first gill-cleft. Ctzcilia in S. America; Siphonops 

 in Brazil and Mexico ; Epicrium in Ceylon ; Ichthyophis (Fig. 240), 

 Indian and Malayan. 



Stegocephali or Labyrinthodontia. 



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. They are fatally sensitive to salt. 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 atrd) 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 respiration 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, and a lung-breathing 

 tailed larva 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 



