Nearly all geckos are nocturnal and the pupil contracts into a vertical slit, except in a few diurnal kinds, e.g. _Phelsuma_ of islands in the Indian Ocean, and _Lygodactylus_ of Africa. _Aelurosaurus_ of Borneo and Australia, and _Ptenopus_ of South Africa, have upper and lower movable eyelids. Whilst the skin is mostly soft on the back, with little granular tubercles, scales (except on the belly) are absent, but they are present in _Homopholis_, in _Geckolepis_ of Madagascar, and most fully developed in _Teratoscincus scincus_. This peculiar little inhabitant of the steppes and desert regions of Turkestan and Persia, by rubbing the imbricating scales upon each other, produces a shrill cricket-like noise, whilst sitting at night in front of its hole in the ground. Furthermore it is so thoroughly adapted to running upon the desert sand that its digits are devoid of adhesive lamellae. The same beautiful adaptation to the surroundings exists also in _Ptenopus_ (with fringed toes) and _Stenodactylus_, which are likewise deserticolous. _Aeluronyx_ of Madagascar and Seychelles has cat-like retractile claws. _Naultinus elegans_ of New Zealand is said to be viviparous; the others lay but one rather large egg at a time. Many species have a feeble voice which resembles a repeated click of the tongue, and their name "gecko" is supposed to be an Indian imitation of the sound. 2. Family, _Uroplatidae._--Amphicoelous; parietals separate; but the nasal bones are fused together, and the clavicles are not dilated. Genus _Uroplates_, with a few species, e.g. _U. fimbriatus_ in Madagascar. 3. Family, _Eublepharidae._--Procoelous; parietals united; eyelids functional; clavicles expanded as in the true geckos which they resemble in other respects. The few genera and species are undoubtedly a heterogeneous assembly, as indicated by their very scattered distribution, but they all agree in their decidedly handsome colour pattern, bands of dark brown to maroon upon a light ground. _Eublepharis_, with one species each in Panama, Mexico, Texas and California; two in India. _Coleonyx elegans_ in forests of Central America and Mexico. _Psilodactylus_ in West Africa. II. Suborder, CHAMAELEONTES. Acrodont, Old World lizards, with laterally compressed body, prehensile tail and well developed limbs with the digits arranged in opposing, grasping bundles of two and three respectively. The chameleons (q.v.) have many structural peculiarities. III. Suborder, LACERTAE. Procoelous vertebrae; ventral portions of the clavicles not dilated; parietal bones fused into one.