Lizard

Lizard (Lat. lacerta1), a name originally referred only to the small European species of four-legged reptiles, but now applied to a whole order (Lacertilia), which is represented by numerous species in all temperate and tropical regions. Lizards are reptiles which have a transverse external anal opening (instead of a longitudinal slit as in Crocodilians and tortoises) and which have the right and left halves of the mandibles connected by a sutural symphysis. The majority are distinguished from snakes by the possession of two pairs of limbs, of external ear-openings and movable eyelids, but since in not a few of the burrowing, snake-shaped lizards these characters give way entirely, it is well-nigh impossible to find a diagnosis which should be absolutely sufficient for the distinction between lizards and snakes. In such doubtful cases a number of characters have to be resorted to, and, while each of these may fail when taken singly, their combination decides the question. It is certain that the snakes have been evolved as a specialized branch from some Lacertilian stock, and that both “orders” are intimately related, but it is significant that it is only through the degraded members of the lizards that recent representatives of the two great groups seem to run into each other. Such critical characters are:—

  | Lizards. | Snakes.  
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Limbs | 2 pairs, 1 or 0. | 0 or vestigial hind-limbs.  
Ear-opening | Usually present. | Always absent.  
Eyelids | Mostly movable. | No movable lids.  
Tongue | Often not retractile. | Always bifid and retractile into itself.  
Teeth | Pleuro- or acrodont, not anchylosed. | Acrodont, anchylosed.  
Mandibles | Mostly firmly united suturally. | Never with suture, mostly ligamentous.  
Columella cranii | Mostly present. | Absent.  
  | Mostly with bony arches across |    
  |  the temporal region. | No bony arches.  
  | Osteoderms common. | No osteoderms.  
  
The lizards and snakes are the two dominant reptilian orders which are still on the increase in species, though certainly not in size. As a moderate estimate, the number of recent species of lizards is about 1700. As a group they are cosmopolitan, their northern limit approaching that of the permanently frozen subsoil, while in the southern hemisphere the southern point of Patagonia forms the farthest limit. As we approach the tropics, the variety of forms and the number of individuals increase, the most specialized and developed forms, and also the most degraded, being found in the tropics. In the temperate regions they hibernate. The majority live on broken ground, with or without much vegetation; many are arboreal and many are true desert animals, while a few are more or less aquatic; one, the leguan of the Galapagos, Amblyrhynchus, even enters the sea. Some, like the majority of the geckos, are nocturnal. In adaptation to these varied surroundings they exhibit great variety in shape, size and structure. Most of these modifications are restricted to the skin, limbs, tail or tongue. Most lizards live on animal food, varying from tiny insects and worms to lizards, snakes, birds and mammals, while others prefer a mixed or an entirely vegetable diet. Accordingly, the teeth and the whole digestive tract are modified. But swiftness, the apparatus necessary for climbing, running and digging, the mechanism of the tongue, the muscles of the jaws (hence modifications of the cranial arches) stand also in correlation with the kind of food and with the way in which it has to be procured. Generally the teeth are conical or pointed, more rarely blunt, grooved or serrated. They are inserted either on the inner side of the margin of the jaws (pleurodonta) or on the edge of the bones (acrodonta). The tongue is generally beset with more or less scaly or velvety papillae and has always a well-marked posterior margin, while the anterior portion may or may not be more or less retractile into the posterior part.

In many lizards the muscles of the segments of the tail are so loosely connected and the vertebrae are so weak that the tail easily breaks off. The severed part retains its muscular irritability for a short time, wriggling as if it were a living creature. A lizard thus mutilated does not seem to be much affected, and the lost part is slowly reproduced. This faculty is of advantage to those lizards which lack other means of escape when pursued by some other animal, which is satisfied with capturing the detached member.

The motions of most lizards are executed with great but not enduring rapidity. With the exception of the chameleon, all drag their body over the ground, the limbs being wide apart, turned outwards and relatively to the bulk of the body generally weak. But the limbs show with regard to development great variation, and an uninterrupted transition from the most perfect condition of two pairs with five separate clawed toes to their total disappearance; yet even limbless lizards retain bony vestiges beneath the skin. The motions of these limbless lizards are similar to those of snakes, which they resemble in their elongate body.

The eggs are elliptical in shape, both poles being equal, and are covered with a shell which may be thin and leathery or hard and calcareous. The number of eggs laid is small in comparison with other reptiles, rarely exceeding a score, and some like the anolids and the geckos deposit only one or two. The parents leave the eggs to hatch where they are deposited, in sand or in mould. Many lizards, however, retain the eggs in the oviducts until the embryo is fully developed; these species then bring forth living young and are called ovo-viviparous by purists. Some lizards possess a considerable amount of intelligence; they play with each other, become very tame, and act deliberately according to circumstances. As a rule the Iguanids and Varans are as bright as the Agamas are dull. Many have the power of changing colour, a faculty which they share only with various frogs, toads and fishes. Lizards are not poisonous, with the single exception of Heloderma.

The Lacertilia, or lizards in the wider sense, fall easily into three natural groups: geckos (q.v.), chameleons (q.v.) and lizards.

I. Suborder, Geckones. Pleurodont lizards with well-developed limbs; without temporal bony arches; postthoracic ribs united across the abdomen. Tongue, thick and broad, slightly nicked anteriorly. With few exceptions they have amphicoelous vertebrae, the parietal bones remain separate and they have no eyelids, with very few exceptions.

1\. Family, Geckonidae.—Amphicoelous; parietals separate; clavicles dilated and with a perforation near the ventral end. Cosmopolitan, although mainly tropical, with about 270 species (see Gecko).

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.

The general appearance is too misleading for the classification of the Lacertae. E. D. Cope (Proc. Ac. Philad., 1864, pp. 224 et seq. and Proc. Amer. Ass. xix., 1871, p. 236, &c.) therefore relied upon more fundamental characters, notably the presence or absence of osteoderms, the formation of the skull, the teeth and the tongue. G. A. Boulenger (Ann. Nat. Hist. 5, xiv., 1884, p. 117, &c.) has further improved upon the then prevailing arrangements, and has elaborated a classification which, used by himself in the three volumes of the catalogue of lizards in the British Museum, is followed in the present article with slight alterations in the order of treatment of the families. In the following diagnoses of the families preference is given to such characters as are most easily ascertained.

The 17 “families” fall into 4 or 5 main groups. Presumably the presence of osteoderms and of complete cranial arches are more archaic than their absence, just as we conclude that limbless forms have been evolved from various groups possessed of fully developed limbs. Zonuridae and Anguidae assume a central position, with Agamidae and Iguanidae as two parallel families (not very different from each other) of highest development, one in the Old World, the other in America. Xenosaurus seems to be an offshoot intermediate between the Iguanidae and the Anguidae; a degraded form of latter is perhaps Aniella of California, whilst Heloderma and Lanthanotus are also specialized and isolated offshoots. A second group is formed by the few American Xantusiidae, the numerous American Tejidae, and the burrowing, degraded American and African Amphisbaenidae. A third group comprises the cosmopolitan Scincidae, the African and Malagasy Gerrhosauridae which in various features remind us of the Anguidae, and the African and Eurasian Lacertidae which are the highest members of this group. Anelytropidae and perhaps also Dibamidae may be degraded Scincoids. The Varanidae stand quite alone, in many respects the highest of all lizards, with some, quite superficial, Crocodilian resemblances. Lastly there are the few Pygopodidae of the Australian region, with still quite obscure relationship.

Family 1. Agamidae.—Acrodont; tongue broad and thick, not protractile; no osteoderms. Old World.

The agamas have always two pairs of well-developed limbs. The teeth are usually differentiated into incisors, canines and molars. The skin is devoid of ossifications, but large and numerous cutaneous spines are often present, especially on the head and on the tail. The family, comprising some 200 species, with about 30 genera, shows great diversity of form; the terrestrial members are mostly flat-bodied, the arboreal more laterally compressed and often with a very long tail. Most of them are insectivorous, but a few are almost entirely vegetable feeders. They are an exclusively Old World family; they are most numerous in Australia (except New Zealand) and the Indian and Malay countries; comparatively few live in Africa (none in Madagascar) and in the countries from Asia Minor to India.

The majority of the ground-agamas, and the most common species of the plains, deserts or rocky districts of Africa and Asia, belong to the genera Stellio and Agama. Their scales are mixed with larger prominent spines, which in some species are particularly developed on the tail, and disposed in whorls. Nearly all travellers in the north of Africa mention the Hardhón of the Arabs (Agama stellio), which is extremely common, and has drawn upon itself the hatred of the Mahommedans by its habit of nodding its head, which they interpret as a mockery of their own movements whilst engaged in prayer. In some of the Grecian islands they are still called korkordilos, just as they were in the time of Herodotus. Uromastix is one of the largest of ground-agamas, and likewise found in Africa and Asia. The body is uniformly covered with granular scales, whilst the short, strong tail is armed with powerful spines disposed in whorls. The Indian species (U. hardwicki) is mainly herbivorous; the African U. acanthinurus and U. spinipes, the Dab of the Arabs, take mixed food. Phrynocephalus is typical of the steppes and deserts of Asia. Ceratophora and Lyriocephalus scutatus, the latter remarkable for its chameleon-like appearance, are Ceylonese. Calotes, peculiar to Indian countries, comprises many species, e.g. C. ophiomachus, generally known as the “bloodsucker” on account of the red colour on the head and neck displayed during excitement. Draco (see Dragon) is Indo-Malayan. Physignathus is known from Australia to Cochin China.

Of the Australian agamas no other genus is so numerously represented and widely distributed as Grammatophora, the species of which grow to a length of from 8 to 18 in. Their scales are generally rough and spinous; but otherwise they possess no strikingly distinguishing peculiarity, unless the loose skin of their throat, which is transversely folded and capable of inflation, be regarded as such. On the other hand, two other Australian agamoids have attained some celebrity by their grotesque appearance, due to the extraordinary development of their integuments. One (fig. 1) is the frilled lizard (Chlamydosaurus kingi), which is restricted to Queensland and the north coast, and grows to a length of 3 ft., including the long tapering tail. It is provided with a frill-like fold of the skin round the neck, which, when erected, resembles a broad collar. This lizard when startled rises with the fore-legs off the ground and squats and runs on its hind-legs. The other lizard is one which most appropriately has been called Moloch horridus. It is covered with large and small spine-bearing tubercules; the head is small and the tail short. It is sluggish in its movements, and so harmless that its armature and (to a casual observer) repulsive appearance are its sole means of defence. It grows only to a length of 10 in., and is not uncommon in the flats of South and West Australia.

Family 2. Iguanidae.—Pleurodont; tongue broad and thick, not protractile; no osteoderms. America, Madagascar and Fiji Islands.

According to the very varied habits, their external appearance varies within wide limits, there being amongst the 300 species, with 50 genera, arboreal, terrestrial, burrowing and semi-aquatic forms, and even one semi-marine kind. All have well-developed limbs. In their general structure the Iguanidae closely resemble the Agamidae, from which they differ mainly by the pleurodont dentition. Most of them are insectivorous. Some, especially Anolis and Polychrus, can change colour to a remarkable extent. The family ranges all through the neotropical region, inclusive of the Galapagos and the Antilles, into the southern and western states of North America. Remarkable cases of discontinuous distribution are Chalarodon and Hoplodon in Madagascar, and Brachylophus fasciatus in the Fiji Islands. Conolophus subcristatus and Amblyrhynchus cristatus inhabit the Galapagos; the former feeds upon cactus and leaves, the latter is semi-marine, diving for the algae which grow below tide-marks. For Basiliscus see Basilisk; Iguana is dealt with under its own heading; allied is Metopoceros cornutus of Hayti. Polychrus, the “chameleon,” and Liolaemus are South American; Ctenosaura of Central America and Mexico resembles the agamoid Uromastix. Corythophanes and Laemanctus, with only a few species, are rare inhabitants of the tropical forests of Central America and Mexico. Sauromalus, Crotaphytus, Callisaurus, Holbrookia, Uma, Uta are typical Sonoran genera, some ranging from Oregon through Mexico. Allied is Sceloporus, with about 34 species, the most characteristic genus of Mexican lizards; only 4 species live in the United States, and only 3 or 4 are found south of the Isthmus of Tehuantepec and are restricted to Central America. The majority are humivagous, while others are truly arboreal, e.g. S. microlepidotus, a species which, moreover, has the greatest possible altitudinal range, from the hot country of southern Oaxaca to the upper tree-line of Citlaltepetl, about 13,500 ft. elevation; many species are viviparous. Phrynosoma, with about a dozen species, the “horned toads” of California to Texas, and through Mexico. Some of these comical-looking little creatures are viviparous, others deposit their eggs in the ground. They are well concealed by the colour of their upper parts, which in most cases agrees with the prevailing tone of their surroundings, mostly arid, stony or sandy localities; the large spikes on the head protect them from being swallowed by snakes. The enlarged spiny scales scattered over the back look as if it were sprinkled with the dried husks of seeds. They are entirely insectivorous, bask on the broiling hot sand and then can run fast enough; otherwise they are sluggish, dig themselves into the sand by a peculiar shuffling motion of the fringed edges of their flattened bodies, and when surprised they feign death. The statement, persistently repeated (O. P. Hay, Proc. U.S. Nat. Mus. xv., 1892, pp. 375-378), that some, e.g. P. blainvillei of California, have the power of squirting a blood-red fluid from the corner of the eye, still requires renewed investigation.  
  
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Fig. 1.—Frilled Lizard (Chlamydosaurus kingi).  
  
The smallest lizards of this family belong to the genus Anolis, extremely numerous as regards species (more than 100) and individuals on bushes and trees of tropical America, and especially of the West Indies. They offer many points of analogy to the humming birds in their distribution, colours and even disposition. Hundreds may be seen on a bright day, disporting themselves on trees and fences, and entering houses. Like the iguanas, they (at least the males) are provided with a large, expansible dewlap at the throat, which is brilliantly coloured, and which they display on the slightest provocation. This appendage is merely a fold of the skin, ornamental and sexual; it has no cavity in its interior, and has no communication with the mouth or with the respiratory organs; it is supported by the posterior horns of the hyoid bone, and can be erected and spread at the will of the animal. The presence of such dewlaps in lizards is always a sign of an excitable temper. Many, e.g. A. carolinensis, the “chameleon,” can change colour to an extraordinary degree. They are much fed upon by birds and snakes, and have a fragile tail, easily reproduced. They bring forth only one large egg at a time, but probably breed several times during the season.

Family 3. Xenosauridae.—Pleurodont; solid teeth; anterior part of tongue slightly emarginate and retractile, and covered with flat papillae; no osteoderms. Mexico.

The only representative of this family is Xenosaurus grandis, recorded from the mountains of Orizaba, Cordoba and Oaxaca. The four-footed creature is less than 1 ft. in length; the body is depressed, covered above with minute granules and tubercles; a distinct fold of skin extends from the axilla to the groin, reminding of the similar fold of some Anguidae, to which this singular genus seems to be allied.

Family 4. Anguidae.—Pleurodont; teeth solid, sometimes (Ophiosaurus) grooved; anterior part of tongue emarginate and retractile into the posterior portion; osteoderms on the body, and especially on the head where they are roofing over the temporal fossa; entirely zoophagous and ovo-viviparous. America, Europe and India.

Gerrhonotus, 8 species, in mountainous countries, from British Columbia to Costa Rica; like Diploglossus s. Celestus of Mexico, the Antilles and Central America, with well-developed limbs, but with a lateral fold. Anguis fragilis and two species of Ophiosaurus are the only members of this family which are not American, and even the third species of Ophiosaurus, O. ventralis, lives in the United States. Ophiosaurus s. Pseudopus, the glass-snake, from Morocco and the Balkan peninsula to Burma and Fokien; also in the U.S.A., with the limbs reduced to a pair of tiny spikes near the vent, and a lateral fold along the snake-like body. Anguis, with its sole species fragilis, the slow-worm or blind-worm, is devoid of a lateral fold, and the limbs are entirely absent. Europe, Algeria and western Asia.

Family 5. Helodermatidae, with Heloderma of Arizona and Mexico, and Lanthanotus of Borneo.—The teeth of Heloderma are recurved, with slightly swollen bases, loosely attached to the inner edge of the jaws; each tooth is grooved, and those of the lower jaw are in close vicinity of the series of labial glands which secrete a poison; the only instance among lizards.2 Limbs well developed. Tongue resembling that of the Anguidae. The skin of the upper surface is granular, with many irregular bony tubercles which give it an ugly warty look. H. horridum in Mexico, and H. suspectum, the gila monster, in the hot and sandy lowlands of the Gila basin. The animal, which reaches a length of more than 2 ft., is blackish-brown and yellow or orange, and on the thick tail these “warning colours” are arranged in alternate rings. Small animals are probably paralyzed or killed by the bite, the poison being effective enough to produce severe symptoms even in man. The Zapotecs, who call the creature Talachini, and other tribes of Mexico have endowed it with fabulous properties and fear it more than the most poisonous snakes. Lanthanotus corneensis, of which only a few specimens are known, is apparently closely allied to Heloderma, although the teeth are not grooved, osteoderms are absent and probably also the poison glands.

Family 6. Aniellidae.—One genus, Aniella, with a few worm- or snake-shaped species in California, which seem to be degraded forms of Anguidae. The eyes and ears are concealed, the limbs are entirely absent, body and tail covered with soft, imbricating scales. The tongue is villose, smooth, bifid anteriorly. The few teeth are recurved, with swollen bases. The skull is much reduced. Total length of A. pulchra up to 8 in.

Family 7. Zonuridae.—Pleurodont; tongue short, villose, scarcely protractile, feebly nicked at the tip. With osteoderms at least upon the skull, where they roof in the temporal region. Africa and Madagascar.

Only 4 genera, with about 15 species. Zonurus of South Africa and Madagascar has the whole head, neck, back and tail covered with strong bony scales, the horny covering of which forms sharp spikes, especially on the tail. They defend themselves by jerking head and tail sidewards. Z. giganteus reaches 15 in. in length, and is, like the other members of the family, zoophagous. The other genera live in southern and in tropical Africa: Pseudocordylus, Platysaurus and Chamaesaura; the latter closely approaches the Anguidae by its snake-shaped body, very long tail and much reduced limbs, which in C. macrolepis are altogether absent.

Family 8. Xantusiidae.—Pleurodont; tongue very short and scaly; no osteoderms; supratemporal fossa roofed over by the cranial bones; eyes devoid of movable lids; tympanum exposed; femoral pores present; limbs and tail well developed. American.

Xantusia (so named after Xantus, a Hungarian collector), e.g. X. vigilis and a few other species from the desert tracts of Nevada and California to Lower California. Lepidophyma flavomaculatum, Central America; and Cricosaura typica in Cuba.

Family 9. Tejidae.—Teeth solid, almost acrodont; tongue long and narrow, deeply bifid, beset with papillae; no osteoderms; scales of the back very small or quite granular; limbs sometimes reduced. America.

This large, typically American family comprises more than 100 species which have been arranged in many genera. Some are entirely arboreal, dwellers in forests, while others, like Cnemidophorus and Ameiva, are strictly terrestrial, with great running powers; a few dwell below the surface and are transformed into almost limbless worm-shaped creatures. The family is essentially neotropical. Of its several dozen genera only two extend through and beyond Central America: Ameiva into the eastern and western Hot-lands of Mexico, Cnemidophorus (monographed by H. Gadow, Proc. Zool. Soc., 1906, pp. 277-375) through Mexico into the United States, where C. sexlineatus, the “swift,” has spread over most of the Union. Tupinambis teguixin, the “teju” of South America and the West Indies, is the largest member of the family; it reaches a length of a yard, most of which, however, belongs to the strong, whip-like tail. Teguixin is taken from the Aztec teco-ixin, i.e. rock-lizard, the vernacular name of Sceloporus torquatus which is one of the Iguanidae misspelt and misapplied. The tejus frequent forests and plantations and are carnivorous, eating anything they can overpower. They in turn are much hunted for the sake of their delicate flesh. They defend themselves not only with their powerful jaws and sharp claws, but also with lashing strokes of the long tail. They also use this whip for killing snakes which they are said to eat. Their long-oval, hard-shelled eggs are deposited in the ground. They retire into self-dug burrows. Cophias and Scolecosaurus have very much reduced limbs. In the genus Tejus the teeth of the adult become molar-like; and in Dracaena they are transformed into large, oval crushers, indicating strictly herbivorous habits, while most members of the family live upon animal food.

Family 10. Amphisbaenidae.—The body is covered with soft skin, forming numerous rings with mere vestiges of scales. Worm-shaped, without limbs, except Chirotes which has short, clawed fore-limbs. Eyes and ears concealed. Tongue slightly elongated, covered with scale-like papillae and bifurcating. Tail extremely short. Acrodont or pleurodont. America, Mediterranean countries, and Africa with the exception of Madagascar.

Chirotes canaliculatus, and two other species; Pacific side of Mexico and Lower California. With five, four or three claws on the stout little digging fore-limbs. These pink, worm-like creatures live in sandy, moist localities, burrowing little tunnels and never appearing on the surface. Amphisbaena (q.v.). Rhinëura of Florida, and also known from the Oligocene of South Dakota; Lepidosternum of South America; and Anops in America and Africa; Blanus cinereus, Mediterranean countries. Trogonophis, Pachycalamus and Agamodon of Africa are all acrodont; the other genera are pleurodont. In all about a dozen genera, with some 60, mostly tropical species.

Family 11. Scincidae.—Pleurodont. Tongue scaly, feebly nicked in front. Osteoderms on the head and body. Limbs often reduced. Cosmopolitan. The temporal region is covered over, as in the Lacertidae and Anguidae, with strongly developed dermal ossifications. Similar osteoderms underlie the scales of the body and tail. Femoral pores are absent.

All the skinks seem to be viviparous, and they prefer dry, sandy ground, in which they burrow and move quickly about in search of their animal food. This partly subterranean life is correlated with the frequent reduction of the limbs which, in closely allied forms, show every stage from fully developed, five-clawed limbs to complete absence. Some have functional fore-limbs but mere vestiges of hind-limbs; in others this condition is reversed. In some deserticolous kinds e.g. Ablepharus, the lower eyelid is transformed into a transparent cover which is fused with the rim of the reduced upper lid. The same applies to the limbless little Ophiopsiseps nasutus of Australia. This large family contains about 400 species, with numerous genera; the greatest diversity in numbers and forms occurs in the tropical parts of the Old World, especially in the Australian region, inclusive of many of the Pacific islands. New Zealand has at least 6 species of Lygosoma. America, notably South America, has comparatively very few skinks.

The skink, which has given the name to the whole family, is a small lizard (Scincus officinalis) of 6 or 8 in. in length, common in arid districts of North Africa and Syria. A peculiarly wedge-shaped snout, and toes provided with strong fringes, enable this animal to burrow rapidly in and under the sand of the desert. In former times large quantities of it were imported in a dry state into Europe for officinal purposes, the drug having the reputation of being efficacious in diseases of the skin and lungs; and even now it may be found in apothecaries’ shops in the south of Europe, country people regarding it as a powerful aphrodisiac for cattle.

Mabouia, with many species, in the whole of Africa, southern Asia and in tropical America. M. (Euprepes) vittata, the “poisson de sable” of Algeria, is semi-aquatic. Chalcides s. Seps, of the Mediterranean countries and south-western Asia, has a transparent disk on the lower eyelid which is movable; limbs very short or reduced to mere vestiges. Lygosoma circumtropical; Eumeces, also with many small species, in America, Africa and Asia. Cyclodus s. Tiliqua of Australia, Tasmania and Malay Islands, has stout lateral teeth with rounded-off crowns; C. gigas of the Moluccas and of New Guinea is the largest member of the family, reaching a length of nearly 2 ft.; the limbs are well developed, as in Trachysaurus rugosus of Australia, which is easily recognized by the large and rough scales and the short, broad, stump-like tail.

Family 12. Anelytropidae.—An artificial assembly of a few degraded Scincoids. The worm-shaped body is devoid of osteoderms. The tongue is short, covered with imbricating papillae and slightly nicked anteriorly. Teeth pleurodont. Anelytropsis papillosus, of which only three specimens are known, from the humus of forests in the state of Vera Cruz. Eyes concealed. Typhlosaurus and Feylinia in tropical Africa and Madagascar.

Family 13. Dibamidae.—Dibamus novae-Guineae of New Guinea, the Moluccas, Celebes and the Nicobar Islands. Tongue arrow-shaped, covered with curved papillae. The vermiform body is covered with cycloid imbricating scales, devoid of osteoderms. Limbs and even their arches are absent, excepting a pair of flaps which represent the hind-limbs in the males.

Family 14. Gerrhosauridae.—Pleurodont. Tongue long, with papillae, like that of the Lacertidae but only feebly nicked anteriorly. Osteoderms on the head and body, roofing over the temporal region. Femoral pores present, also mostly a lateral fold. Limbs sometimes reduced to small stumps. Tail long and brittle. The few genera and species of this family are restricted to Africa, south of the Sahara and Madagascar.

Gerrhosaurus, with lateral fold and complete limbs; Tetradactylus also with a fold, but with very variable limbs; Condylosaurus; all in Africa. Zonosaurus and Tracheloptychus in Madagascar.

Family 15. Lacertidae.—Pleurodont. Tongue long and bifid, with papillae or folds, with osteoderms on the head but not on the body. Limbs always well developed. Palaearctic and palaeotropical with the exception of Madagascar; not in the Australian region.

The Lacertidae or true lizards comprise about 20 genera, with some 100 species, most abundant in Africa; their northern limit coincides fairly with that of the permanently frozen subsoil. They all are terrestrial and zoophagous. The long, pointed tail is brittle.  
  
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Fig. 2.—Heads of British Lizards. a, Lacerta vivipara; b, L. agilis; c, L. viridis.  
  
Most of the European lizards with four well developed limbs belong to the genus Lacerta. Only three species occur in Great Britain (see fig. 2). The common lizard (Lacerta vivipara) frequents heaths and banks in England and Scotland, and is locally met with also in Ireland; it is viviparous. Much scarcer is the second species, the sand-lizard (Lacerta agilis), which is confined to some localities in the south of England, the New Forest and its vicinity; it does not appear to attain on English soil the same size as on the continent of Europe where it abounds, growing sometimes to a length of 9 in. Singularly, a snake (Coronella laevis), also common on the continent, and feeding principally on this lizard, has followed it across the British Channel, apparently existing in those localities only in which the sand-lizard has settled. This lizard is oviparous. The males differ by their brighter green ground colour from the females, which are brown, spotted with black. The third British species, the green lizard (Lacerta viridis), does not occur in England proper; it has found a congenial home in the island of Guernsey, but is there much less developed as regards size and beauty than on the continent. This species is larger than the two preceding; it is green, with minute blackish spots. In Germany and France one other species only (Lacerta muralis) appears; but in the south of Europe the species of Lacerta are much more numerous, the largest and finest, being L. ocellata, which grows to a length of 18 or 20 in., and is brilliantly green, ornamented with blue eye-like spots on the sides. Even the small island-rocks of the Mediterranean, sometimes only a few hundred yards in diameter, are occupied by peculiar races of lizards, which have attracted much attention from the fact that they have assumed under such isolated conditions a more or less dark, almost black, coloration. L. muralis, with its numerous varieties, has been monographed by G. A. Boulenger, Trans. Zool. Soc. xvii. (1905), pp. 351-422, pl. 22-29.

Other genera are Psammodromus and Acanthodactylus in south-western Europe and northern Africa. Cabrita in India, with transparent lower eyelids. Ophiops, likewise with transparent but united lids, from North Africa to India.

Family 16. Varanidae.—Pleurodont. Tongue very long, smooth and bifid. Osteoderms absent. Limbs always well developed. Old World.

This family contains only one genus, Varanus, with nearly 30 species, in Africa, Arabia and southern Asia, and Australia, but not in Madagascar. The generic term is derived from the Arabic Ouaran, which means lizard. Owing to a ridiculous muddle, this Arabic word has been taken to mean “warning” lizard, hence the Latin Monitor, one of the many synonyms of this genus, now often used as the vernacular. Many of the “monitors” are semi-aquatic, e.g. V. niloticus, and these have a laterally compressed tail; others inhabit dry sandy districts, e.g. V. scincus, the ouaran el ard of North Africa; others prefer wooded localities. V. salvator is the largest species, reaching a length of 7 ft.; it ranges from Nepal and southern China to Cape York; a smaller species, common in New Guinea and Australia, is V. gouldi. They all are predaceous, powerful creatures, with a partiality for eggs. Their own eggs are laid in hollow trees, or buried in the sand. The young are prettily spotted with white and black ocelli, but the coloration of the adult is mostly very plain.  
  
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Fig. 3.—Monitor of the Nile (Varanus niloticus).  
  
The following families are much degraded in conformity with their, in most cases, subterranean life. They are of doubtful relationships and contain each but a few species.

Family 17. Pygopodidae.—Pleurodont, snake-shaped, covered with roundish, imbricating scales. Tail long and brittle. Fore-limbs absent; hind-limbs transformed into a pair of scale-covered flaps. Tongue slightly forked. Eyes functional but devoid of movable lids. Australia, Tasmania and New Guinea.

Pygopus, e.g. P. lepidopus, about 2 ft. long, two-thirds belonging to the tail, distributed over the whole of Australia.

Lialis burtoni, of similar size and distribution, has the hind-limbs reduced to very small, narrow appendages. The members of this family seem to lead a snake-like life, not subterranean, and some are said to eat other lizards. L. jicari, from the Fly river, has a very snake-like appearance, with a long, pointed snout like certain tree-snakes, but with an easily visible ear-opening; their eyelids are reduced to a ring which is composed of two or three rows of small scales.

(H. F. G.)

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1 For the etymology of this word, see Crocodile.

2 For anatomical detail and experiments, see R. W. Shufeldt, P. Z. S. (1890), p. 178; G. A. Boulenger, ibid. (1891), p. 109, and C. Stewart, ibid. (1891), p. 119.