ADAPTATIONS 95 



of spaces analogous in their action to suckers on the under side 

 of the feet ; this surface on each toe being divided into such 

 spaces by means of a series of tranverse plates in the skin. 

 When the foot is pressed upon a flat surface the soft, and yield- 

 ing plates are squeezed flat and the air between them is con- 

 sequently driven out. Elevation of the centre of the foot, 

 which in some cases is webbed, consequently produces vacuums 

 between the plates which act as suckers ; these vacuums being 

 rendered more effectual than would otherwise be the case in the 

 non-webbed species by the presence of a number of minute hairs 

 on the edges of the plates. This sucker-like structure is pre- 

 sent on the feet of many if not most geckos. In certain species, 

 such as Teratosaurus scincus, of Persia and Turkestan, which 

 have forsaken their climbing habits in favour of an existence 

 on desert sands, the clinging apparatus has been lost or modi- 

 fied, so that the foot has reverted to a more normal type. 



Another modification in connection with climbing is ex- 

 hibited by the hind-feet of the iguanas, which attains its maxi- 

 mum development in the chamaeleon-iguanas of the genus Anolis. 

 In these reptiles the outermost, or fifth toe, is widely separated 

 from the other four, which are elongated, and branches off at 

 the root of the foot, so that its point of origin is higher up than 

 that of the rest. In Anolis it looks quite distinct from the rest 

 of the foot, and the whole foot is designed to form an efficient 

 climbing instrument. 



A few lizards, such as some of the American iguanas, and 

 more especially the frilled lizard {Clilamydosaurus kingi) of 

 Australia, whose bodies are formed on the compressed arboreal 

 type, have deserted to a greater or less degree their original 

 climbing habits, and taken to an existence on open sandy 

 ground, where they run at times on the hind-legs, in the up- 

 right posture with the fore-limbs folded and hanging by the 

 sides of the body ; the large throat-frill of the Australian species 

 being on such occasions folded up like a badly-made umbrella. 

 The frilled lizard cannot, however, maintain this running gait 

 for any length of time; and after a bit will either turn to bay 

 at the foot of a tree, or run up the stem of the latter in the 

 manner of a climbing lizard. The frilled lizard is a member of 

 the Agamidce. The same cursorial type occurs in certain 

 smaller carnivorous representatives of the extinct dinosaurs, 



