IV. VERTEBRATA: REPTILIA, SQUAMATA. 599 



Section II. CRASSILINGUIA. Tongue thick, fleshy, not protrusible from 

 the mouth, or only slightly so. IGUANIOE ; American, often a comb of 

 spines on the back, teeth pleurodont, i.e., firmly united to the inner side 

 of the jaw. Three hundred species. Anolis,* Sceleporus* Phrynosoma* 

 * horned toads.' AGAMID.E; Old World, teeth acrodont, i.e., seated on the 

 angle of the jaw bones. One hundred and fifty species. Chlamydosaurus, 

 Draco volans, with ribs greatly elongate and supporting a dermal fold 

 which acts as a parachute. 



Section III. FISSILINGUIA. Tongue long and thin, divided at the tip, 

 and capable of wide protrusion from the mouth, and in Varanus retractile 

 into a sheath. TEJID^E ; American, teeth acrodont ; Cnemidophortts* 

 Tejus. HELODERMATIDJS, pleurodont ; Heloderma,* the ' Gila monsters,' are 

 the only poisonous lizards. LACERTILID^E (Lacerta) and VARANID^E (Vara- 

 nus, the monitors) are Old World forms, Lacerta vivipara bringing forth 

 living young. 



Section IV. BREVILINGUIA. Tongue short, slightly notched at the tip, 

 slightly protrusible. Four hundred species. SCINCID^, with tendency to 

 reduction of the limbs. Eumeces,* Oligosoma* In Anguis and Typhline 

 the legs are absent. ZONURID.E, with a finely scaled groove along the side; 

 all Old World except our Ophisaurus ventralis,* the glass snake, a limb- 

 less form with brittle tail. 



Section V. ANNULATA. In many respects snake-like ; legs and epi- 

 pterygoid, tympanum, and movable eyelids lacking and usually girdles ; 

 tropical or subtropical. In Chirotes sternum and reduced fore legs 

 retained. AmpliisbcBna. 



Section VI. VERMILINGUIA ; includes the Old World chameleons (our 



FlG.628. Head of chameleon with tongue extended. 



' chameleon ' is Anolis, supra} with long fleshy tongue, lying rolled up in 

 the mouth, but protrusible and used for catching insects, its end being 

 covered with a sticky mucus. Other characteristics are the ring-like eye- 

 lids functioning as an iris, the climbing feet in which the toes are united 

 into two opposable groups; epipterygoids, clavicle, sternum, and tympanic 

 membrane lacking. The chameleons are best known from their changes 

 of color, produced by rapid alterations in the size and shapes of the 

 chroinatophores. Color changes occur in other lizards, but not to such an 

 extent as here. 



