ADAPTATIONS 117 



parallel to Ablepharus, the large and transparent lower eyelid 

 being welded with its reduced fellow. 



Adaptive modifications for protecting the ear and the 

 nostrils from the intrusion of water or sand have been inde- 

 pendently developed in many reptiles, for instance, desert- 

 dwelling lizards on the one hand, and crocodiles on the other. 

 In some cases the apertures of these organs are capable of being 

 more or less completely closed by means of valves or fringes, 

 while in other instances they are reduced to the size of mere 

 pin-holes. 



A large number of reptiles, living and extinct, have de- 

 veloped a bony armour in the skin, varying considerably in the 

 different groups, and in many cases at any rate independently 

 evolved. Very generally this bony armour, which is situated 

 in the deep layer of the skin, is overlain by horny shields, 

 which may or may not correspond with the bony plates beneath. 

 In some of the extinct dinosaurs, such as Scelidosaurus and 

 Stegosaurus, the dermal armour along the back is developed into 

 bony plates and spines, probably sheathed during life in horn. 

 At first sight the spines which fringe the back of many of the 

 iguanas of the present day might well appear to correspond in 

 structure (as they undoubtedly do in function) with the dorsal 

 spines of these dinosaurs. As a matter of fact this is not the 

 case, the spines of all the iguanas being nothing more than 

 specially developed horny scales, and therefore of epidermal 

 origin ; none of the members of the family Ignanida develop- 

 ing bony plates in the skin. Of the same horny nature are the 

 spines on the body, limbs, and tail of the horned toads {Phryno- 

 soma), which likewise belong to the same family. These rep- 

 tiles have, however, true bony spines on the back of the head 

 and along the sides of the lower jaw ; these being attached to 

 the skull itself, and therefore structurally comparable to the 

 head-spines of the horned dinosaurs. The Agamidce form 

 another family of lizards characterised by the absence of 

 dermal bony structures ; accordingly the spines which cover 

 the entire head, body, limbs, and tail of the oft-mentioned 

 moloch lizard {Moloch horidus) are entirely epidermal horny 

 structures. The same is the case with the spines girdling the 

 tails of the agamoid lizards, of the genus Uromastix, and several 

 other instances of the same nature might be cited. Never- 



