REPTILIA 247 



success in outlasting the great reptilian orders that have come and 

 gone; in that the generalized types that do not go to excesses of spe- 

 cialization are able to weather the age-long vicissitudes of world 

 change, adapting themselves to new conditions and always plastic 

 enough to adjust themselves to a new environment. 



Characters of Lacertilia. It is not so simple a matter as one 

 might think to set up distinctions between lizards and snakes. One 

 might think that the presence of legs in the lizards and their absence 

 in snakes would readily separate the two groups; but there are limb- 

 less lizards and there are snakes with at least rudimentary legs. The 

 vast majority of lizards, however, have well-developed legs, only a 

 few degraded burrowing forms being limbless. The lizards also have 

 no elastic ligament between the two halves of the lower jaw as in the 

 snakes. The ventral scales are usually smaller than the dorsal. 



The Lacertilia may be divided into three sub-orders: Geckones, 

 Lacertae and Chamaeleontes. 



Sub-order 1. Geckones. The geckos (Fig. 138, A) are primitive 

 lizards with the following peculiarities: four-footed; amphiccelous 

 vertebrae; no bony temporal arches; dilated clavicles; separate 

 parietals; eyes with movable lids; tongue broad, fleshy, protrusible 

 and nicked on the end. 



The geckos are practically cosmopolitan within the warm temper- 

 ate countries. In the United States they are confined to our south- 

 western Pacific regions. They are wonderful climbers. By means of 

 adhesive pads on the toes they are able to ascend the smoothest 

 surfaces such as walls, ceilings, or even window-panes. Adhesion is 

 accomplished by the vacuum-cup principle, but the "cup" consists 

 of a complicated system of lamellae. They feed on all sorts of small 

 animals, especially insects and spiders. They are absolutely harmless 

 to man in spite of an undeserved reputation for venomousness. 

 Their chief defense consists of an extremely loosely articulated tail, 

 which comes off with great readiness when seized. When cornered 

 and in grave danger they wag the tail over the body, appearing to 

 offer it for seizure. The enemy is usually satisfied and the tailless 

 gecko proceeds to regenerate another tail, which fortunately it is able 

 to do very readily. 



Sub-order 2. Lacertae. To this group belong the great majority 

 of modern lizards. As many as eighteen families of Lacertee are dis- 

 tinguished by the authorities, but in a volume of the present scope it 



