202 REPTILES OF THE WORLD 



of lateral undulations. Most snakes are agile swim- 

 mers; the members of one subfamily — the Hydropliince 

 — have a vertically compressed tail, like a paddle; they 

 pass their entire life in the sea. Many snakes are strictly 

 arboreal and these are generally much elongated, reaUy 

 whip-like. Some snakes are quite subterraneous, boring 

 their way into the ground like worms; larger species 

 burrow at times in sandy places and often have a scoop- 

 shaped snout. 



The scaly covering of snakes is overlaid with a thin 

 skin that is regularly shed, not in patches, as among most 

 of the lizards, but carefully divested entire. Some time 

 before this event the colors of the reptile fade decidedly 

 and the eyes become white, like bubbles filled with smoke. 

 This condition may last a couple of weeks. Then the 

 reptile suddenly takes on a nearly normal appearance. 

 The eyes look bright and the colors fairly intense. This 

 change is caused by the attack of an oily secretion upon 

 the undersurface of the old skin, loosening that member 

 preparatory to shedding. The snake soon rubs the 

 epidermis back from the top of the head, shedding the 

 eye plates, then rubs the skin from the lower jaw, after 

 which preparation it crawls out of the old cuticle, turning 

 it wrong side out for the entire length of the body and 

 tail. Healthy and well-nourished snakes shed their skin 

 at intervals of about two months apart, or at shorter 

 periods. 



The ophidians either lay eggs or produce their young 

 alive. There is a much larger proportion of viviparous 

 species than among lizards. The young of the poison- 

 ous snakes are provided at birth with perfectly formed 

 venom-conducting fangs and glands; they are just as 

 dangerous, in proportion to their size, as their parent. 

 All young snakes at once shift for themselves after 



