ADAPTATIONS 91 



spotted rocks upon which they delight to bask in the sun. On 

 the other hand, desert-haunting species are more usually of a 

 sandy tint. 



The extreme development of the depressed type of bodily 

 form occurs in species which dwell on sandy or other soft soil , 

 where the body can be closely pressed to the ground ; this 

 supreme development being found in species belonging to dif- 

 ferent family groups, thus demonstrating that its origin is de- 

 pendent on adaptation to habits and environment and has 

 nothing to do with zoological affinity. The best example of 

 this is afforded by the two lizards respectively known as the 

 moloch (Moloch horridus) of the deserts of Western and 

 Southern Australia, and the American so-called " horned toad" 

 {Phrynosoma cornutum), which inhabits similar situations in 

 California. The former — the sole representative of its genus — 

 belongs to the family Agamidce, while the latter, which is one 

 out of about a dozen species of the same genus, is a member of 

 the Iguanidcs. Both have the body so depressed and flattened 

 that it is nearly oval in shape ; and in both, the head, body, 

 and tail are covered with a number of short spines, evidently 

 either for protection or to aid in concealment. In the moloch 

 the colour is pale brown blotched with chocolate, while in the 

 horned toad the prevailing tint is a mixture of yellow, brown, 

 grey, and black. When squatting closely down in the sands of 

 their native deserts, with which the colour of each harmonises, 

 both these lizards must be difficult to detect ; and when they 

 are recognised, their prickly coats must render them difficult to 

 pick up. Any non-scientific person seeing the two species side 

 by side would almost certainly declare that they must be near 

 relations ; whereas their superficial resemblance to one another 

 is a case of parallelism in development for the purpose of 

 adaptation to their surroundings and consequent concealment 

 from enemies (PI. V.). The iguanas of the genus Sceloponts 

 are also depressed terrestrial forms, quite unlike the arboreal 

 compressed representatives of the family. 



The spiny-tailed lizards (Uromastix) of the deserts of the 

 Old World, which belong to the same family as the moloch, 

 may be cited as other examples of the depressed type of body, 

 although the depression is not carried to the same degree as in 

 the instances described above. The spiny-tails are burrowing 



