44 REPTILES 



A few words may be devoted to some of the features of 

 desert reptiles- — a subject which has been studied by Dr. 

 Boettger, in the steppes of Transcaspia. In that district the 

 winter, although comparatively short, is of great severity, while 

 the summer is remarkable for its intense heat. The advent of 

 spring clothes the ground with a carpet of lilies, tulips, and 

 other flowers ; but their season is short, the heat of summer 

 and the autumnal sandstorms reducing the country to a desert. 

 The scattered vegetation has mostly narrow, or even needle-like 

 leaves ; and the sand-heaps round the root of each plant form 

 harbours for the lizards and snakes, the limited number of 

 species of which abound in individuals. Among the most 

 characteristic desert types are various skinks, such as Chalcides 

 and Teratosaurus, certain geckos which have forsaken the 

 normal habitats of the group for this kind of existence, species 

 of Phrynocephalus among the Agamidce, four members of 

 the family Lacertidce, and Varanus griseus representing the 

 monitors. Neither are snakes wanting, the harmless kinds 

 being represented by about half a score of species, among 

 which the sand-burrowing Eryx jaculus is a well-known type ; 

 while the venomous sorts include the asp or cobra, and the 

 sand-viper (Echis arenicola). Most of these reptiles are 

 sandy brown in colour, marked with dark spots or stripes ; and 

 many of them exhibit other adaptations. The lizards and 

 snakes are, for instance, markedly elongated, while the latter 

 have an unusually large number of horny shields on the lower 

 surface of the body. Some have the muzzle specially shaped 

 for digging in the burning sand ; and in others the scales are 

 so arranged as to retain the sand when heaped up on the back. 

 In most of the snakes the nostrils are protected by valves, or 

 much reduced in size ; but in the burrowing species they are 

 situated on the top instead of in the front of the snout. The 

 ears are also protected in a similar manner. Most remarkable 

 of all these adaptations is the presence of a "window" in the 

 lower eyelid of the skinks of the genera Mabuia and Ablepha- 

 rus ; the two eyelids being fused together in the latter. A 

 similar arrangement obtains in certain typical lizards. None 

 of these desert reptiles aestivates. 



Crocodiles and alligators may be cited as examples of 

 reptiles that asstivate when their haunts are desiccated ; burying 



