108 THE STORY OF REPTILE LIFE. 



It must not be supposed, however, that these are 

 the only features which serve to distinguish the 

 snakes. Some others we shall discuss as we 

 proceed, but the majority are of too technical a 

 nature to claim mention here. 



Having briefly indicated the superficial differ- 

 ences between the lizard and the snake, we may 

 proceed to rapidly survey the more important 

 structural features of the latter. 



The covering of the body is invariably fur- 

 nished by scales, and these are never supple- 

 mented by bony plates or nodules. Symmetrically 

 arranged on the head, in the form of shields, 

 these scales afford useful characters for the 

 purposes of classification. Those of the body 

 are small in size, save only those along the under 

 surface, which take the form of narrow bands or 

 shields ranged in a consecutive series at right 

 angles to the long axis of the trunk. They play 

 an important part in locomotion. 



At least once a year, generally much more 

 frequently, the horny outer layer of the skin 

 is shed, and this is done in such a way that 

 not only is it turned completely inside out, but 

 the exact shape of its late owner is preserved, 

 even the peculiar " watch-glass " over the eye 

 being undisturbed. These diaphanous snakes 

 may often be picked up where snakes are 

 common. Only in the Sea-snakes is the skin 

 shed in flakes. 



If, by any mischance, the skin is not shed, 

 death inevitably follows ; the old envelope be- 

 coming so tough and hard as to form an unyield- 

 ing shell, preventing not only the further growth, 



