XII ADAPTATION TO ENVIRONMENT 493 



about, and around the roots of each shrub the wind accumulates 

 little nidunds of sand and dust, a place of retreat for rodents, 

 lizards, snakes, and even for the female tortoises. (!. TJadde's 

 " law of the steppe " is in full force ; — there is little change of 

 forms in a wide district, but all these forms are peculiar, and 

 they congregate socially in great numbers. Most characteristic 

 are those kinds of Geckos whicli, like Teratoscincus, cf. p. 507, 

 have become inhabitants of sand instead of climbers of rocks and 

 trees; various kinds oi Phrynocephalus, cf. p. 5 21, and Varanus 

 griseus ; the four desert-species of Lacertidae are brownish-grey 

 or sandy yellow, with conspicuous stripes or spots. Of snakes 

 are to be mentioned Eryx jaculus, digging in the sand, and 

 about ten other non-poisonous snakes. Tro2ndo7iotus is, of course, 

 restricted to permanently watery places, where they can get 

 frogs and fishes. Of poisonous snakes there is the Cobra and 

 Echis arenicola. Of Amphibia only Biifn viridis and Eana 

 esculenta var. ridihunda exist in suitable places, but there are 

 neither Tree-frogs nor Newts. 



Characteristic features of these inhabitants of the desert are 

 the following : — 



1. Velocity. The Lizards are slender. The Sand -snake, 

 I'cphi-ometopon, is whip-like ; even the Cobra has a relatively 

 narrow^er .and longer tail than the Indian specimens, although 

 tlie number of the vertebrae and of the scales is the same. All 

 tlie desert-snakes are remarkable for the great number of their 

 ventral shields, two hundred and more. 



2. Hard, scaly covering, for instance in Agama, Ecliis, Gymno- 

 dactylus, Teratoscincus; the latter with its fish-like scales is 

 exceptional among Geckos, resembling the likewise deserticolous 

 Geckolepis and Homopliolis of Africa. 



3. Capacity for digging in the sand in order to escape 

 great cold, or burning heat. All the Lizards and the Tortoise, 

 Tcstudo horsjieldi, have strong claws. The snakes Typhlops and 

 Eryx dig with their specially modified snouts, and their tails are 

 very short and blunt. The Sand-viper, Echis, has the scales of 

 the back arranged in very oltlique rows, so that it can heap 

 sand upon its body by wriggling, shaking, and vip-and-down 

 motions of the body. The Agamoid Phrynocephcdus does this 

 by means of lateral folds of the skin. 



4. Arrangements for running; on sand. Tlie lizarel Eremias 



