22 2 SNAKES. 



has become an annual joke, conclude that all sea snakes are 

 similarly mythical. 



Admitting it to be a dubious creature, with neither name 

 nor ancestry in ophidian annals, I must not give it precedence 

 of the recognised water snakes ; but it shall figure in the 

 heart of my book notwithstanding. 



^ Fresh-zvater snakes' form the fourth, and ^ Sea snakes' 

 the fifth of the five groups into which Dr. Giinther has 

 separated the ophidian families ; but the gradations between 

 the land and the fresh-water species, and between the latter 

 and the salt-water snakes or the true HydropJiidce^ are, like 

 all other herpetological features, extremely close. There 

 are water-loving land snakes and land-frequenting water 

 snakes, that is, those which are equally at home in both. 

 In the true water species, however, we find modifications of 

 ordinary rules which show them to be peculiarly protected 

 and adapted for an aquatic existence. 



One notable characteristic in all, both salt-water and fresh, 

 is the position of the nostrils on the top of the snout, and in 

 many these are protected by a valve which closes at will. 

 As air-breathing animals they must come to the surface, but 

 the timid, stealthy ophidian instinct which seeks to hide 

 from observation can be indulged even in the water, with 

 the nostrils so situated that only a very small surface of the 

 head need be exposed. Could we examine the interior of 

 the mouth we should doubtless find some slight variation in 

 the position of the glottis also. In a foregoing chapter we 

 saw that the trachea opens exactly opposite to and close 

 behind what Dumeril calls the 'arriere-narines ;' 'leur glotte 

 qui est a deux levres et qui represente un larynx tres simple. 



