GECKO, a general term applied to any lizard of the family Geckonidae. For the most part geckoes are small creatures with a soft skin, a short, stout body, large head and weak limbs ; the most salient constant characteristic of the group is the absence of connivent eyelids, the eyes, which are usually large and promi nent, being protected by a transparent, watchglass-like covering which is probably a modified nictitating membrane.
The group is cosmopolitan in distribution, occurring every where in warmer climates, even on the remotest oceanic islands, and is adapted to very diverse habitats. All its members are insectivorous and the great majority have the digits modified for climbing; the fingers and toes are dilated either terminally or at their bases and the lower surface of the dilation is covered with transverse plates whose arrangement is exceedingly diverse in the different genera; each plate is beset with numerous tiny, hair like processes which give the whole surface a velvety appearance. When the feet are placed on any surface the velvety pile accomo dates itself to the slightest irregularities and pressure forces the air out from between the hairs ; the resulting vacuum gives suffi cient adhesion to enable many species to climb absolutely smooth and vertical surfaces and even to run across a whitewashed ceiling. Claws are well developed in most species and, in a few, are provided with a special sheath, into which they are retractile. The most remarkable modification of the feet is found in the genus Palmatogecko from the deserts of Damaraland ; here there is no adhesive apparatus but the toes are webbed to their extremities to enable the animal to walk over and burrow into the loose sand.
The tail is extremely fragile and is quickly regenerated, the new one having a simpler scalation than the original. Often the tail is peculiar in shape; it may be long and tapering or short and blunt, or even globular; in one species (Gymnodactylus platyurus) it is leaf-shaped. It seems highly probable that in many instances, particularly where it is large and globular, the tail serves as a storehouse of reserve nutriment on which the animal can draw during unfavourable conditions. As a rule the skin is soft and delicate, and covered with minute granules, but frequently there are large tubercles intermixed with these. Teratoscincus, a western Asiatic desert dweller, has, however, developed large, overlapping smooth scales which enable it to slip through the sand with the minimum of friction. Colours as a rule are drab, greys, browns, and dirty whites predominating, and to the weird and forbidding aspect thus produced the general prejudice against those creatures in the countries where they occur, which has led to their being classed with toads and snakes, is no doubt to be attributed. Their bite was supposed to be venomous, and their saliva to produce painful cutaneous eruptions; even their touch was thought suf ficient to convey a dangerous taint. It is needless to say that in this instance the popular mind was misled by appearances. The geckoes are exceedingly useful creatures, feeding on insects. Many species have a voice, the call differing with the species but being usually a feeble click or chirp. All species so far as known are oviparous, the eggs being white, hard-shelled and usually laid beneath the bark of trees or attached to the under side of leaves.
(H. W. P.)