188 FIRST LEBSOm IN ZOOLOGY. 



server to distinguish between the glass-snake and the ordi- 

 nary snake. Indeed, there are snakes with rudimentary 

 legs, such as the boas, as well as lizards without limbs. 

 Thus, the snakes are really lizards without legs, for there 

 are no very important marks to distinguish one order from 

 the other, except that snakes in general are without limbs 



Fig. 194. — Head and tail of Amphisbmna. (Natural size.) 



and eyelids, and the scales on the head are arranged differ- 

 ently from those of lizards ; and the jawbones are movable, 

 so that a snake can open its mouth very wide and swallow 

 a large animal. 



Indeed, the lizards are ancient forms and the snakes are 



much more recent in their appearance, and everything 



goes to show that the snake-form is the result of adaptation 



■^ ^ to their peculiar mode of life. 



At all events, snakes are very 



common. There are many 



species ; we have 130 species 



Fig. 195.—^, head of Striped Adder. • j.t, tt -j. j cix ^ i m 



(Natural size.) B, head of Green m the United btates ; and all 



contrive, in spite of their want 

 of legs, to gain a living and to play a part in the world of 

 animated existence which no other creatures can assume. 

 Thus, while most snakes run on the ground, others live al- 

 most entirely on trees and shrubs, and still others exclu- 

 sively in the sea. 



The skeleton and internal organs are curiously modified 

 in accordance with the shape of the body and its needs. 



Notwithstanding the fact that snakes have no legs, they 

 can creep, glide, grasp, suspend themselves, erect them- 

 selves, leap, dart, bound, swim, and dive. The peculiar 



