THE VERTEBRATES 209 



protrusible, and usually red or blue-black, serves as a special 

 organ of touch. Hearing is poor, the ears being very little 

 developed. The sense of sight is also probably not at all 

 keen. Snakes rely chiefly on the sense of smell for finding 

 their prey and their mates. The colors of snakes are often 

 brilliant, and in many cases serve to produce an effective 

 protective resemblance by harmonizing with the usual 

 surroundings of the animal. The food of snakes consists 





FIG. 107. A garter-snake, Thamnophis parietalis. (Photograph from 

 life by J. O. Snyder.) 



almost exclusively of other animals, which are caught alive. 

 Some of the poisonous snakes kill their prey before swallow- 

 ing it, as do some of the constrictors. While most snafces live 

 on the ground, some are semi-arboreal and others spend 

 part or all of their time in the water. Cold-region snakes 

 spend the winter in a state of suspended animation; in the 

 tropics, on the contrary, the hottest part of the year is spent 

 by some species in a similar "sleep." 



Among the commonest members of this group are the 

 garter-snakes (fig. 107), always striped, and not more than 

 three feet long. The most widespread species is rather 

 dully colored, with three series of small dark spots along 

 each side. The common water-snake is brownish, with 

 back and sides each with a series of about eighty large, 



