THE TRANSITION TO LAND 



391 



in areas of human population. However, they make up only a small 

 proportion of the total number of snakes in the world, and it is certainly 

 not fair to condemn an entire group of animals just because there are 

 some undesirables in their midst. It is much more sensible to learn 

 which are not desired and destroy those and preserve the others which 

 are of value. 



It is easy to learn the poisonous snakes in the United States, for there 

 are only four types that can bite a person, and these have easily recog- 

 nized characteristics. Three of them are pit vipers which take their 



Courtesy Ross Allen's Reptile Institute 



Fig. 26.14. Milking a rattlesnake. This large rattlesnake is having its venon ex- 

 tracted at Ross Allen's Reptile Institute in Silver Springs, Florida. Venom collected 

 in this manner is used in producing antivenin serum. 



name from the pit which lies just anterior and ventral to the eye. Also, 

 the pupil of the eye is slit-like, such as the pupil of a cat's eye, rather 

 than round, as is found in the other families of snakes. Some are per- 

 haps thinking that it does no good to know what kind of eye the pit 

 vipers have because they are not going to get close enough to see the 

 pupils anyway. However, it is perfectly safe to get near enough to see 

 the pupil clearly, for the snake will not attack a person and they can 

 strike no farther than half their body length. The third characteristic 

 of the pit vipers is the arrow-shaped head, caused by an enlargement of 

 the head at its junction with the neck. Other snakes may show this 



