I G U I G U 701 by the tail, they are able to part so readily with the portion seized. The tongue is generally short and not deeply divided at its extremity, nor is its base retracted into a sheath; it is always moist and covered with a glutinous secretion. The prevailing colour of the iguanas is green ; and, as the majority of them are arboreal in their habits, such colouring may be generally regarded as protective. Those on the other hand which reside on the ground have much duller, although as a rule equally protective hues ; thus Darwin observed on the shore at Bahia a terrestrial member of this family, which from its mottled appearance could hardly be distinguished from the surrounding surface. Iguanas, however, possess to an extent only exceeded by the chameleon the power of changing their colours, their brilliant green becoming transformed in an instant, under the influence of fear or irritation, into more sombre hues and even into black. They differ greatly in size, from a few inches to several feet in length. One of the largest and most widely distributed is the common iguana (Iguana tuberculata), which occurs in South America and the West Indies. It attains a length of 5 feet, and is of a greenish Iguana. colour occasionally mixed with brown, while the tail is surrounded with alternate rings of those colours. Its food consists of vegetable substances, which it obtains from the forest trees among whose branches it lives and in the hollows of which it deposits its eggs. These are of an oblong shape, about an inch and a half in length, and are said by travellers to be very pleasant eating, especially when taken raw, as they usually are, and mixed with farina. They are timid, defenceless animals, depending for safety on the comparative inaccessibility of their arboreal haunts and their protective colouring, which is rendered even more effective by their remaining still on the approach of danger. Otherwise they exhibit few signs of animal intelligence. "The iguana," says Bates (The Naturalist on the Amazon), " is one of the stupidest animals I ever met. The one I caught dropped helplessly from a tree just ahead of me ; it turned round for a moment to have an idiotic stare at the intruder, and then set off run ning along the path. I ran after it and it then stopped as a timid dog would do, crouching down and permitting me to seize it by the neck and carry it off." Along with several other species the common iguana is much sought after in tropical America ; the natives esteem its flesh a delicacy, and capture it by slipping a noose round its neck as it sits in fancied security on the branch of a tree. Although chiefly arboreal, many of the iguanas take readily to the water ; and there is at least one species, Orcocephalus cristatus, which leads for the most part an aquatic life. These marine lizards occur only in the Galapagos Islands, where they are never seen more than 20 yards inland, while they may often be observed in companies several hundreds of yards from the shore, swimming with great facility by means of their flattened tails. Their feet are all more or less webbed, but in swimming they are said to keep these organs motionless by their sides. Their food consists of marine vegetation, to obtain which they dive beneath the water, where they are able to remain, without coming to the surface to breathe, for a very considerable time. Though they are thus the most aquatic of lizards, Mr Darwin, who studied their habits during his visit to those islands, states that when frightened they will not enter the water. Driven along a narrow ledge of rock to the edge of the sea, they preferred capture to escape by swimming, while if thrown into the water they immediately returned to the point from which they started. A land species belonging to the allied genus Trachycephalus also occurs in the Galapagos, which differs from most of its kind in forming burrows in the ground. IGUANODON, a genus of extinct Dinosaurian reptiles, the remains of which have been found in greatest abund ance in the Wealden, a delta formation of the south-east of England. They also occur, though more sparingly, in the Lower Greensand, where lately (1879) Professor Prestwich announced the discovery in the " Kimmeridge Clay " of what are as yet the earliest known remains of these reptiles. Although no complete skeleton of the iguanodon has been found, such bones of it as have been obtained prove it to have been one of the largest terrestrial animals known. Thus its femur in one instance measured from 4 to 5 feet in length, with a circumference of 22 inches at its narrowest part. These and other measurements led Dr Mantell the original discoverer of Iguanodon and others to conclude that it probably attained a length of from 50 to 60 feet. Its front limbs appear to have been small, while the hind pair attained enormous development, and from the structure of the latter, which may be regarded as intermediate between those of existing reptiles and of birds, the iguanodon is supposed to have either habitually or occasionally walked on its hind legs like a bird. This supposition is rendered all the more probable by the discovery in the same strata of gigantic three-toed footsteps in pairs such as might have been formed by the iguanodon had it walked in this bipedal manner. The teeth of these animals formed one of their most marked characteristics, bearing a striking resemblance to the teeth of existing iguanas in their blade-like form and serrated edges, but ! differing from these as well as from those of all other known I reptiles in internal structure. Like existing iguanas they
- were probably herbivorous, using their teeth for cutting
- and tearing their tough vegetable food; unlike these,
however, they appear to have used their teeth also for the purpose of mastication. This is shown by the deeply worn condition in many cases of the crowns of their teeth, which, from being sharp and incisor-like, gradually assumed a molar-like form. As the old teeth were thus reduced by " tear and wear," they were gradually replaced by a fresh dental crop. The front portion of the jaws was destitute of teeth, the upper part being beak-like, while the lower
waa hollowed out like the same region in the parrot.
