116 STORY OF THE REPTILES 



aquatic tortoise-forms sink into the bottoms of ponds 

 .and streams; the more terrestrial burrow — some onlj 

 to a very shallow depth. A pet tortoise may get very 

 anxious about burying itself long before severe cold 

 comes on. Snakes seek deep crevices in rocks, and 

 all kinds, of different species, are said to ball them- 

 selves together — often in a mixed mass of various spe- 

 cies. Lizards hibernate in any crevice. Crocodiles 

 do not live generally far enough north to need a 

 winter sleep. But in South America and other ex- 

 tremely hot haunts — where long droughts occur — 

 these crocodilians bury themselves in the mud and 

 lie incased in dried -up dirt, as is the case with some 

 fishes and amphibians, till the rains come again. 



Haunts and Disteibution 



Perhaps enough has been said to indicate the 

 homes of the various reptiles. Their distribution 

 over the earth is peculiar, and so extensive that it 

 can not be discussed here. They are a so much older 

 race than the mammals and birds that the same 

 natural areas for these latter do not answer for the 

 reptiles, which doubtless populated a large area before 

 the others came in. Unlike the amphibians, they were 

 not so much confined by salt water, though they seem 

 to be largely fresh-w^ater forms, now and in fossil times. 



Migration 



Reptiles may be said to migrate only in the sense 

 that some, as the sea-turtles, are known to resort year 



