■M-J. 



FHOGS, 'HIADS, AND SALAMANUKUS 



passed on land. Since tlie exivW, or lavval sta^e, of these 

 animals is })assedin the water, uujst o( the larva' ai-e fui'nished 

 with gills for breathing. .Vdult ainiiliiliians that live in the 

 water all their lives retain the gills throughout life. Those, 



however, tiiat live on 

 land during the adult 

 stage lose the gills, ara 1 

 ha\e lungs instead. 

 \ They differ from the 

 hshes in having seg- 

 mented Umbs instead 

 of fins. They are 

 cokl bloodeil. The 

 ni i]orityliavesniooth, 

 fecaleless skins. 



Adaptations to en- 

 vironment. — Note 

 that the tadpoles of 

 amphibians which hve 

 in the water have 

 gills to suit such an 

 environment; but when dry land is substituted for water, 

 the gills are lost and lungs appear. Again, the necturus 

 and the siren that live in the water all their lives retain the 

 gills throughout life, as best .suited to such an environTuent. 

 Tadpoles of frogs and toads are provided with broad, 

 flat tails for swimming; but the atlult frogs and toads are 

 tailless. .Man)' fi-ogs are excellent swimmers, however, 

 because of their weblied toes and the adaptations of their 

 legs to such a purpo.se. The webbed toes of some species 

 of the tree frogs of the Malaysian Islands (Fig. 170) have 

 become much enlarged antl adapted to rjuite a different 



Fig. 169. — Tree toad on the bark of a tree. 



