The Living Things of the Earth unit i 



Fig. 3:5 The garter snake. This snake is one of the conunoiicst found in the United 

 States. It is frequently seen on farms, even near the bnildings, and frequently, also, in 

 lawns and gardens of thickly settled connimnities. The garter snake may bite when 

 it is handled rmighly, but its bite is harmless, except as a possible source of infection. 

 It does not lay its eggs as many other snakes do. The eggs hatch within the mother s 

 body and the young are born alive. All snakes move by wriggling and by many small 

 inoveinents of their ribs which are attached to the sharp scales on their underside. 



(U. S. BUIUEAU OF BIOLOGICAL SURVEY) 



to the size of the body; there are very 

 powerful breast muscles which move 

 these win^s. The breast bone to w hich 

 the muscles are attached and many other 

 bones are hollow, making the body ex- 

 ceptionally light in weight. 



In the bibliography at the end of the 

 book there are listed several books about 

 birds. Perhaps you will wish to read 

 one of them and learn more about birds. 



CLASS - REPTILES 



What is a reptile? Like mammals and 

 birds, reptiles have lungs. Some la\- eofrs 

 as do the birds; some bring forth their 

 young alive. But they differ from mam- 

 mals and birds in that they are covered 

 with scales. Scales, you remember, are 

 characteristic of fish also. How, then, 

 can one distinguish between reptiles and 

 fish? This is easy, for fish in ocneral 

 get air from the water by means of gills. 



and their scales arc slinn'. Reptiles have 

 lungs and dv\ scaly skins. 



Reptiles are the first vertebrate ani- 

 mals you have met in this book that are 

 cold-blooded. The body of the cold- 

 blooded animal is sometimes \\arni and 

 sometimes cold, depending on the sur- 

 roundings. Reptiles are most common in 

 the tropics; as you go north\\'ard you 

 may expect to find fewer and fewer rep- 

 tiles. In a climate such as that of the 

 northeastern states where A\inters are 

 cold, reptiles are active and visible during 

 only a short season. As fall comes on 

 they become sluggish and soon go into 

 a state of hibernation (winter sleep) un- 

 derground. Some reptiles run on four 

 legs, some on two, while some wriggle 

 without an\' legs at all. Many live on 

 land; others dwell in fresh water or in 

 the salt\- ocean. Zoologists divide them 

 into three main orders which \'ou can 

 easil\ recognize: the snakes and lizards, 



