108 REPTILES OF THE WORLD 



Yet there are geckos having round pupils; but such 

 species live in open sandy places and are diurnal. 



The tongue of a gecko is thick, fleshy and viscid. It 

 is capable of considerable protrusion though little em- 

 ployed as an organ of investigation. In catching the 

 insect prey the tongue is decidedly useful as the animal 

 stalks its quarry, then rushes, and if the latter be small 

 it is snapped up by the sticky organ in a manner peculiar 

 to all the thick -tongued lizards. 



Not all of the geckos are thick-bodied, stumpy-tailed 

 and have adhesive digits. Among them are certain 

 species that have wearied of a wall-climbing life and 

 taken to the ground. With such Evolution has been 

 busy in adapting them to widely different conditions 

 than experienced by the ancestral forms. The average 

 gecko lives on the trunks of trees, the faces of cliffs or 

 walls, traversing smooth, vertical surfaces with re- 

 markable facility owing to its expanded digits — even 

 running at remarkable speed on the underside of flat, 

 horizontal surfaces — like a ceiling. Such is the repre- 

 sentative gecko, a nocturnal animal that seldom runs 

 over the ground. The exceptional species have actually 

 taken to the fine sands of the open deserts, where their 

 wall-climbing relations would be as awkward as a tor- 

 toise in the water. Note the consequent development 

 along lines of adaptation for a life on the sands! The 

 body is lighter and more slender than that of the 

 climbing forms, and the tail is more elongated. The 

 adhesive digits have disappeared and in the place of 

 "suckers" which would be quite useless, in fact, a 

 hindrance to a sand-running creature, we find the toes 

 to be slender and furnished on each side with a project- 

 ing fringe of scales; the fringes acting as admirable sup- 

 ports in keeping the foot from sinking into the sand. 



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