Page:EB1911 - Volume 16.djvu/846

 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: (q.v.),  (q.v.) and lizards.

I. Suborder,. 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 ).

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,. 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 (q.v.) have many structural peculiarities.

III. Suborder,. 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 ) 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