THE ATRACTASPIS VIPERS. 



245 



fangs. Tlie fangs are abnormally developed, so much so that I 

 do not think it possible for the jaws to be opened sufficiently wide 

 for the snake to inflict a bite. Most of the solid teeth have dis- 

 appeared, or are in a rudimentary condition. There can be little 

 doubt but that these Atractaspis vipers once had the general 

 appearance and habits of other members of the family, but 

 owing to their taking to burrowing habits, their outward form has 

 gradually been undergoing a change, and doubtless in course of time 

 the fangs will disappear or become considerably smaller. Owing 

 to its habit of burrowing, this genus of snake is seldom found. 



The Atractaspis Vipers furnish us with an illustration of what 

 Darwin means by the Evolution of species. Here we have a 

 Viper which, through changing climate and other conditions, took 

 to burrowing habits. The whole anatomy of the creature has 

 been slowly modified to suit its new environment. 



Fig. ioi (a). — 35B. Fangsof an Atractaspis Adder. Its nose is sharp and hard, and suited for digging 

 in soft ground, and its body is smooth and formed for ghding through loose earth and sand 

 with the minimum amount of resistance and friction. 



Fig. ioi (6).— Bibron's Adder (Atractaspis hibronii). 



