94 THE STORY OF REPTILE LIFE. 



consequence of a change in its habits, the precise 

 nature of which it is not easy to understand. 

 The transformation seems to be due to adapta- 

 tion to life in a sandy habitat, where escape from 

 enemies is made by burrowing, and prey of a 

 sluggish disposition or helpless character is to be 

 captured without chase, and without the effort 

 of climbing. By a perfectly natural transition 

 we are led to the consideration of some yet 

 more curious forms, highly specialised in some 

 respects, degenerate in others. These are the 

 amphisbsenas. 



Only one species, belonging to the genus 

 Chirotes, possesses limbs, and these are repre- 

 sented by vestiges of the fore-limbs. For the 

 rest, the amphisbsenas are entirely limbless, and 

 resemble worms rather than lizards. This 

 peculiarity is traceable to the fact that they lead 

 an entirely subterranean life, and have in con- 

 sequence lost all external evidence of both eyes 

 and ears. With the glass-snakes and the other 

 surface-dwelling forms burrowing is a secondary 

 feature in the life-history of the animal, and has 

 in consequence involved certain minor modifica- 

 tions only the protection of the eyes by a trans- 

 parent window formed by the lower eyelid, 

 closely-fitting scales, and the absence of limbs. 

 Bearing in mind the fact that the moles, and 

 other quite unrelated mammalian burrowing 

 forms, have developed specially powerful arid 

 peculiarly modified limbs, it seems strange that 

 the lizards should have acquired equal skill as 

 burrowers by suppressing the limbs and adopting 

 the model of the lowly earth-worm. But the 



