N-ATCJRAL HISTORY. 319 



' Lo ! the preen serpent, from his dark abode, 

 Which e'en Imagination fears to tread, 

 At noon forth issuine 1 , gathers up his train 

 In orbs immense." THOMSON. 



ORDER III. OPIIIDlA. 



1017. Why is the third order of reptiles termed ophidia ? 



From the Greek ophis, 

 meaning a serpent or snake 

 The order includes all the 

 serpents and snakes, whatever 

 may be their nature or modes 

 of life. They are the only 

 vertebrated animals which 

 have the power of infusing 

 a poison into wounds, 

 though many of them are 

 destitute of this power. 



1018. Why are. serpents unprovided with feet ? 



One reason, at least, may be found for this deprivation in the 

 feet that, as they are adapted for fulfilling certain ends within 

 particular geographical limits, they are confined to those limits by 

 the absence of locomotive organs ? 



If creatures like the boa and the rattle-snake could spread 

 themselves from the hot to the temperate latitudes, and diffuse 

 themselves generally through these, they would prove serious 

 pests, and formidable enemies to a great number of 

 useful races. 



10U*. How are serpents enabled to move along the ground- 

 without feet or legs ? 



Locomotion is effected by the contractile force of the muscles, 

 alternately drawing up and extending the body, combined with 

 the adhesion of the tegumentary covering with the ground. 



The animal attaching to the ground a point near its head 

 contracts its body, or bends it int<> an arch, bringing forward the 



