ADAPTATIONS 93 



most characteristic development by iguanas (Jguanida) and 

 chamaeleons {Chamceleontidce), is precisely the reverse of the 

 terrestrial, that is to say, in place of being depressed, the bod)' 

 is compressed or flattened from side to side, so that the back 

 and bell}' take the form of more or less sharp ridges, while 

 the sides are extensive flattened surfaces. The tail partakes 

 in a greater or less degree of the same modification ; while the 

 limbs, which are often of considerable length, must necessarily 

 be separated from their fellows of the opposite side by a com- 

 paratively small space at the shoulders and haunches. Now 

 it is clear that a reptile of this shape is admirably adapted to 

 escape detection when standing on or clinging to a bough, as 

 it may be easily mistaken for a broken branch, or, if coloured 

 green, for a leaf or bunch of leaves. But chameleons (and for 

 aught I know, iguanas also) go one better than this, for when a 

 stranger approaches the tree or shrub on which they may be 

 resting, every one of them promptly moves to the opposite 

 side of the branch, when its thin body is more or less com- 

 pletely eclipsed. 



In the foregoing paragraph it has been mentioned that 

 iguanas belong to one family of reptiles and chamaeleons to 

 another; from which we see that, like the depressed type, the 

 compressed form has been independently developed in differ- 

 ent groups. This, however, is by no means all, for we find 

 among reptiles of the latter type an instance where species be- 

 longing to different families have acquired a superficial re- 

 semblance analogous to the one existing between the horned 

 toad and the moloch lizard, and due to parallelism in adaptive 

 development. The species between which this resemblance is 

 most marked are the Indian chamaeleon {CJiam<zho calcaratus) 

 on the one hand, and the chameleon-lizard {GaiiyocepJialits 

 diamceleontinus) of the Malay countries on the other ; the 

 former typifying a family by itself, while the latter is a member 

 of the Agamiike. Both spe'cies display the same helmet-like 

 form of the head, the laterally-compressed body, with a sharply 

 keeled back, and the long tapering tail. The general colour of 

 the two is likewise very similar. A certain difference is notice- 

 able with regard to the spines on the back, which are more 

 distinct in the chameleon-lizard ; but such a difference might 

 be specific. Careful examination will show that the two reptiles 



