n] FEATURES OF ENVIRONMENT 39 



night, bury themselves in the sand by various con- 

 trivances. Some have a depressed, somewhat flattened 

 body, and the scales on the sides form rows of ledges, 

 so that a shuffling motion heaps the sand upon the 

 body. The scales are sharply keeled and so arranged 

 in slanting rows that the sand rolls by itself into 

 the required position. This also serves admirably for 

 concealment, and the head, sticking out, is armed or 

 rather dissembled by spikes, which then look like 

 seeds, fallen thorns or broken bits of pebbles strewn 

 over the ground. This is a striking likeness between 

 the so called horned toads, Phrynosoma of North 

 America and Mexico, which are Iguanids, and the 

 Moloch of West Australia and kinds of Phrynoce- 

 phalus of Turkestan, which belong to the family of 

 Agamids. 



Almost all deserticolous lizards are great bur- 

 rowers. Some, which inhabit loose sand, for instance 

 many skinks, are quite smooth, slippery, without any 

 spikes, and the limbs show a great tendency to being 

 reduced to tiny stumps or to disappear altogether. 

 These creatures literally swim wriggling through the 

 sand. In America, Africa and Asia the numerous 

 kinds of the families of skinks and of tejus show 

 stages from fully developed limbs to none, wherever 

 there is a desert. Illustrations of convergent evo- 

 lution. 



The nostrils of such dwellers in dry sand can be 



