9 2 REPTILES 



lizards, which dwell in holes : these they invariably enter head- 

 first, and the spiny tail consequently blocks the entrance in a 

 most effectual manner to all would-be intruders — another in- 

 stance of structural modification and adaptation for protective 

 purposes. Crocodiles also offer an example of the depressed 

 type of bodily form : but since these reptiles are to a great 

 extent aquatic in their habits, the large and powerful tail has 

 assumed a compressed form, so as to act as an oar or rudder 

 in swimming ; its efficiency in this respect being increased by 

 the elevation of the two edges of the upper surface into crests. 



Although this depressed type of body is characteristic of 

 purely terrestrial species, it would be a mistake to suppose that 

 it is entirely confined to reptiles with such habits. On the con- 

 trary, it occurs in species habitually dwelling in trees, or fre- 

 quenting walls or vertical rock-surfaces ; and, strictly speaking, 

 therefore, this type of bodily contour may be met with among 

 arboreal reptiles. It is, however, better to term species with 

 this habit trunk-haunting or wall-haunting reptiles, for they are 

 not arboreal in the sense in which an iguana or a chameleon is, 

 that is to say, they do not dwell on the small branches and 

 amid the leaves, but cling tightly to the bark of the trunk and 

 larger boughs. The best examples of trunk-haunting reptiles 

 with this depressed and expanded type of body are afforded 

 by certain geckos, such as the Turkish gecko (Hemidactylus 

 turcicus) and that variety of the Malagasy bark-gecko known 

 as Uroplates fimbriatus lichenium. In the latter not only is 

 the body greatly depressed and expanded, but the short and 

 trowel-like tail is modified in the same manner ; and since, as 

 already stated, the colouring accords in a marvellous degree 

 with lichen-clad bark, the reptile must be practically invisible 

 when clinging to the trunks it frequents. A further develop- 

 ment of the depressed type of body is presented by the fringed 

 gecko {Ptychozoum homalocephalum) of the Malay countries, in 

 which the sides of the head, body, limbs, and tail are bordered 

 by a thin membrane of considerable width. When clinging to 

 a trunk, this membrane causes the outlines of the body to merge 

 imperceptibly into the bark. If, however, it be true that it also 

 serves as a parachute, this fringe must have a double function, 

 namely as an aid in protection and as an organ of flight. 



The arboreal type of bodily form, as presented in its 



