220 FIRST LFSSONS IN ZOOLOGY 



nating in a fivc-tocd foot; in the lizards the boih' is more 

 elongate, and witli usualU' four legs, but sometimes with 

 two onh', or e\-en none at all ; while in the snakes the 

 long, slender, c}dindrical body is legless, or at most has 

 mere rudiments of the hinder limbs. With the reptiles, 

 locomotion is as often effected by the bending or scrpen- 



Fic. 17S. — V sea-turtle. Cluloiu- })iydi!s. C(:»nimoii in tn-j-iic ncecins. (This 

 turtk- is six feet Imii;: ilrawti from a pli(itut;raph by R. E. Siiodgrass, 

 made on the (lalapai^'os Ishimls. l^icific (_>cean.) 



tine movements of the trunk as b)' the use of the legs. 

 Among lizards and snakes the body is co\'ered -with 

 horn\' epidermal scales or plates, w hile among the turtles 

 and crocotliles there ma)- be, in addition to the epidermal 

 plates, a real deposit of Ijone in the skin wherebx' the 

 effectiveness (jf the armor is increased. The epidermal 

 covering of snakes and lizartls is periodically moulted, 

 or, as we sa)', the skin is shed. The bright colors antl pat- 

 terns of snakes antl of many lizards are due to the presence 

 and arrangement of pigment cells in the skin. Amon<i- 



