THE AMPHIBIA 101 



used by the Australian aborigines as a source of drinking 

 water. Though some of the glomeruli in Cyclorana are 

 small and poorly vascularized, there is no evidence of 

 aglomerular tubules, and no aglomerular amphibian is 

 known. 



There is a single record of frogs and their tadpoles 

 living in salt water in the Phihppines, but it has never 

 been confirmed and it is generally accepted that the 

 Amphibia are incapable of tolerating any degree of sa- 

 linity above that of their blood. For all of them, past 

 and present, sea water can be considered to be quick 

 poison. 



The Amphibia have never conquered the problem of 

 living entirely away from water. It has been said that 

 they are adapted not so much to live on land as to re- 

 main in water by getting from one water hole to an- 

 other. It is not surprising that among many ancient forms 

 (as among some surviving salamanders) the struggle 

 was given up and that the animal has reverted to perma- 

 nent aquatic life, even to the retention of larval gills, as in 

 the mud puppy and some other urodeles. Nevertheless, 

 the complementary relations between the changes in 

 glomerular filtration and water absorption through the 

 skin, both controlled by the pituitary, serve to keep them 

 in water balance so long as they do not move too far 

 away from the water or moist areas, and, viewed his- 

 torically, the Carboniferous Amphibia represent the sec- 

 ond step— the crossopterygian lung being the first— to- 

 ward a truly terrestrial life. 



