More important than any of the preceding is the large and widely distributed family of the Scincidae, comprising a number of small Lacertilians, some of which are completely snake-like, whilst others possess a single pair of limbs, and others again have the normal two pairs of limbs in a well-developed condition. All possess movable eyelids, and in all the conformation of the lower jaw is Lacertilian, and not Ophidian. All the Scincoidean Lizards have the body covered by similar scales overlapping one another like the scales of fishes, whilst the head is protected by larger symmetrical plates. The tongue is free, fleshy, and slightly notched.
Of the snake-like forms of this group, none is more familiarly known than the Blind-worm or Slow-worm (Anguis fragilis, fig. 302) which is found over almost the whole of Europe, in western Asia, and northern
Fig. 302. - The Blind-worm (Auguis fragilis) - after Bell.
Africa, and which is one of the most abundant of the British Reptiles. The Blind-worm possesses no external appearance of limbs, though the scapular and pelvic arches are present in a rudimentary condition. Its appearance is completely serpentiform, and it is vulgarly regarded as a dangerous and venomous animal, but quite erroneously, as it is even unable to pierce the human skin. It is a perfectly harmless animal, living upon worms, insects, and snails, and hibernating during the winter. It derives its specific name of fragilis from the fact that when alarmed it stiffens its muscles to such an extent that the tail can be readily broken off, as if it were brittle.
Numerous other small Lizards are referable to the Scincidae, but it is only necessary to mention the Skinks themselves (Scincus), in which both pairs of limbs are present in a well-developed state. The Skinks are found in almost all the warmer parts of the Old World, and closely-allied forms (such as the West Indian "Galliwasp") are found in the New World. The common Skink (fig. 303) is a native of Arabia and Africa. It attains a length of eight or nine inches, and was formerly used in various diseases as a remedy.
Passing over several small groups, the next family requiring consideration is that of the Lacertidae, comprising the typical Lizards, in which there are always four well-developed limbs, each terminated by five free toes of unequal lengths. The body is covered with scales, which assume the form of shields or "scuta" over the abdomen and on the head, the scales of the former region being square and arranged in transverse bands. The tail is rounded. The tongue is slender, bifid, and protrusible, and the eyes have distinct lids. The only truly British Lizards are the Sand-lizard (Lacerta agilis) and the Viviparous Lizard (Zootoca vivipara); and the commonest form upon the Continent is the graceful little Green Lizard (Lacerta viridis), which also occurs in Jersey. The Lizards of the Old World are represented in America by the Ameivae, some of which attain a length of several feet.
Fig. 303. - The common Skink (Scincus officinalis).
Very closely allied to the true Lizards are the Varanidae or Monitors which are indeed chiefly separated by the comparatively trivial fact that the abdomen and head are covered with small non-imbricating scales, and not with large "scuta." The tongue is protrusible and fleshy, like that of the Snakes. The teeth are lodged in a common alveolar groove, which has no internal border; and there are no palatal teeth. The tail has a double row of carinated scales, and is cylindrical in the terrestrial forms, and compressed in those whose habits are aquatic. The Monitors are exclusively found in the Old World (Asia, Africa, and Australia), and are the largest of all the recent Lacertilia; the Varanus Niloticus of Egypt attaining a length of six feet, and the Hydrosaurus salvator of the East Indian Archipelago attaining to as much as eight feet. The Heloderma horridum of Mexico is sometimes placed here.
The Iguanidae constitute another large family of Lizards, belonging (if the Agamidae be excluded) entirely to the New World. The tongue is thick, fleshy, notched at its extremity only, and not protrusible. Mostly there is a dorsal crest, and a goitre or throat-pouch. The body is covered with imbricated scales. They are often divided into "ground-iguanas," in which the body is flat and depressed, and "tree-iguanas," in which the body is compressed. The members of the genus Iguana itself (fig. 301) are confined to South America and the West Indies, and are distinguished by having the throat furnished with a pendulous dewlap or fold of skin, the edge of which is toothed. The back and tail, too, are furnished with an erect crest of pointed scales. The common Iguana (I. tuberculata) attains a length of from four to five feet, and though not of a very inviting appearance, is highly esteemed as food. The Basilisks (Basiliscus) have the top of the head furnished with a membranous sac, which can be distended with air at will.
The family of the Agamidae is closely allied to that of the Iguanidae proper, and represents it in the Old World. The body is covered with imbricated, generally rhombic, scales ; the tongue is thick and non-protrusible; the eyes have eyelids; and the teeth are implanted on the edge of the bones of the jaws.
The Lizards of this group are distributed over nearly the whole of the Old World (principally Asia, Africa, and Australia), and are either arboreal or terrestrial in habit. Good examples are the Stellio vulgaris of the Levant, the Agama muricata of Australia, and the hideous Moloch horridus of the same country. Here also belongs the curious little Frill Lizard (Chlamydosaurus) of Australia, which has the neck furnished on each side with a membranous plaited frill, which can be erected at will. More remarkable than the above are the little Flying Dragons (Draco) of the East Indies and Indian Archipelago. In these singular little Lizards there is a broad membranous expansion on each side, formed by a fold of the integument, supported upon the five or six posterior or false ribs, which run straight out from the spinal column (fig. 304). By means of these lateral expansions of the skin, the Draco can take long flying leaps from tree to tree, and can pursue the insects on which it feeds ; but the lateral membranes simply act as parachutes, and there is no power of true flight, properly so called.
Fig. 304. - Fore-portion of the skeleton of Draco volans, the tail being omitted, showing the posterior or false ribs supporting the parachute.
The Geckotidae form a large family of Lizards, comprising a great number of species, occurring in almost all parts of the world between and near the tropics. The tongue is wide, flat, scarcely notched at its free extremity, and hardly at all pro-trusible. The eyes are large, mostly with extremely short lids, the pupil mostly vertical and linear, but sometimes circular. The vertebrae are amphicoelous. The teeth are numerous, small, compressed, and implanted on the inner edge of the jaw. The nails (when present) are mostly hooked and retractile, and the toes are furnished below with imbricated plates or with adhesive discs. The animal is generally capable of running on the smoothest surfaces, or suspending itself back-downwards. They feed on insects, and are found in abundance in the warmer parts of both the Old and New Worlds.
Another remarkable family of Lacertilians is that of the
Fig. 305. - Head of Gecko stentor. (After Gunther.)
Chamaekontidae, containing, among other species, the familiar little Chamaeleo Africanus, which occurs abundantly in the north of Africa and in Egypt, and is so well known for its power of changing its colour under irritation or excitement. In this genus the eye (fig. 306) is of large size, and is covered by a single circular lid, perforated centrally by a small aperture, by which the rays of light reach the pupil. The Chameleon is naturally a sluggish animal, but it catches its food, consisting of insects, by darting out its long, fleshy, and glutinous tongue - an operation which it effects with the most extraordinary rapidity.
Fig. 306. - Head of a Chameleon (C. Petersii). (After Gray.)
The tail in the Chameleons is round and prehensile, the body compressed, and the skin like shagreen. The tongue' is long, vermiform, club-shaped in front, and very extensile. The toes are adapted for the arboreal life and scansorial habits of the animal, being so arranged as to form two equal and opposable sets. The lungs are excessively voluminous. The Chameleons are exceedingly sluggish and slow in their movements, and are confined to the warmer parts of the Old World.
The last group of living Lizards which requires notice is that of the Rhynchocephalia, a group comprising only the curious genus Hatteria or Sphenodon, which is so aberrant in its characters that this section may well be regarded as a suborder of Lacertilia. Only one species (H. punctata) of this genus is known, and it inhabits New Zealand.
In this singular form (fig. 307) the vertebrae are amphicoelous, and some of the ribs bear "uncinate processes" similar to those of Birds. The quadrate bone is not movable, and is united by suture with the skull. The teeth are completely amalgamated by anchylosis with the jaws, and are developed in the mandible, praemaxillae, maxillae, and in a longitudinal series upon the palatine bones. The praemaxillary teeth are two in number, and are of large size and scalpriform in shape. The serrated edge of the mandible is received in the groove between the palatine teeth and the cutting edges of the maxillae, the alveolar borders of which are hard and as highly polished as the teeth themselves, the function of which they discharge when the latter are ground down in advanced age. Unlike any other Saurian, Hatteria is devoid of any copulatory organ.
Fig. 307.-Side view of the skull of Hatteria punctata, the lower jaw being removed.