ANIMALS— PHYSICAL ENVIRONMENT 117 



patches occur in the pampas and semi-deserts of 

 South America, and there is a tendency for the 

 individuals of each colony to differ in colour, size, 

 and other characters from those of other colonies. 



The reptiles found in sand are pecuUarly interesting 

 because they show many examples of convergence. 

 Camp, in describing the habits of the reptiles of 

 South-Eastern California, states that in one burrowing 

 snake and three lizards the rostrum is specially 

 developed, protruding beyond the mouth. These 

 lizards belong to several different families, so that 

 this similarity in the rostrum is due to convergence 

 and not to close relationship. 



The same enlargement of the rostrum has been 

 recorded by other authors in several different genera 

 of snakes which burrow in the light soil or sand of 

 arid regions : rather similar are the fringed scales 

 surrounding the eye in some sand-dwelling Uzards. 

 In the Jerboa (Jaculus) the muzzle can be contracted 

 and the nostrils narrowed and almost covered by a 

 fold of skin. It appears that the function of this 

 is to protect the nostrils when the animal is burrow- 

 ing and pushing soil with its broad snout (Anderson 

 and De Winton, and Pocock). 



Certain lizards and snakes possess the power of 

 burrowing into sand with extraordinary rapidity. 

 The lizards which do so do not use their legs, but 

 progress by rapidly bending the body from side to 

 side. In members of the Skink family (Scincidse) in 

 North African deserts this is associated with pro- 

 gressive reduction of the Hmbs, and members of this 

 family exist showing various stages from the normal 



