SNAKES. 113 



bearing ancestors. Why the hind-limbs have 

 persisted so long after the disappearance of the 

 fore-limbs is a point which cannot be answered. 



The peculiarly specialized condition of the 

 body leaves but little room for further modifica- 

 tion for the purpose of locomotion. Hence it is 

 that we find more uniformity in the body than 

 among the lizards. Yet, in spite of specialisation, 

 snakes hold their own among the trees, on the 

 ground, or burrowing beneath its surface, or in 

 the water. Tree-snakes sometimes have the 

 shields of the under surface of the body more 

 or less markedly keeled so as to afford a safer 

 hold, and further have a prehensile tail. 



Keels of this kind are especially well developed 

 in the Tree-Snakes of the genus Dendrophis, natives 

 of South-Eastern Asia and Australia. These have 

 the ventral scales armed with a pair of suture- 

 like keels notched on each side. Therewith they 

 are enabled to glide up the branches of trees in 

 an almost straight line, instead of having to adopt 

 an undulating motion. These snakes attain a 

 length of six feet. Certain new- world tree-snakes 

 of the genus Leptophis, when frightened or shaken 

 out of a tree, coil up the body like a watch-spring, 

 and let themselves drop from considerable heights. 

 Alighting upon the ground on the spiral they 

 escape without injury. Having a very slender 

 body and a long whip-like tail, they are extremely 

 graceful in form, attaining a length of six feet. 

 They feed upon small reptiles, birds, and their 

 eggs. 



The burrowing snakes, like the burrowing 

 lizards, show gradations of adaptation to this 

 H 



