The Common Iguana, I. tuberculata, which inhabits a great part of South America, is one of the best known species of this family. These reptiles are easily recognised from the large pouch underneath the neck, and the dentated crest which extends from the head to the extremity of the tail. The tail, feet, and body are covered with small scales. On the upper part, their colour is a more or less decided green, sometimes becoming blue, at others slate-coloured; the lower part is of a yellowish green. The sides present zigzag, roundish, brown scales, edged with yellow; frequently a yellow line is traced obliquely in front of the shoulder, and some individuals are sprinkled with brown; others have the limbs spotted with brown on a black ground. The tail is surrounded with brownish rays alternating with others green and yellow. When full grown it attains the length of four feet, but the more ordinary length of the animals is about thirty inches. They are very gentle creatures, and perfectly harmless, feeding almost exclusively on vegetables. They are hunted in America for their flesh, which is excellent; and they are especially common at Surinam, in the neighbourhood of Cayenne, and in Brazil.
[Of a kindred species, Metopoceros cornutus, which also is common in the Antilles, an excellent description has been published by Lieutenant Tyler,[22] which we must endeavour to condense. This reptile attains a length of five, and sometimes even of six feet, the tail being about twice and three quarters the length of the body. When first hatched it measures four inches. The mouth is large, and is armed with two rows of maxillary and two of palatal teeth, which appear simply to be intended to crop leaves and to provide the stomach with vegetable food. Each maxillary tooth is a little double-edged saw, and they are so lapped over each other that the reptile, in closing its mouth upon a leaf, cuts through it completely. The tongue is curiously used by the animal to draw food into the mouth, and to forward it down the gullet, or to repel it at will, and the only use of the palatal teeth appears to be to secure the food while the tongue moves forward to afford fresh assistance in its journey down the throat. The tongue is always covered by a glutinous secretion, which is perceptibly appended to the jaws when the mouth is open. Between the lower jaw and the chest is a pouch, which the animal draws in or extends simultaneously with the compression or swelling out of the body when enraged or excited. The portion of the gular pouch attached to the jaw is inflatable, and food is sometimes retained in it for a considerable period, but the lower part is merely extensible.
"Whilst always retaining the same colours, this Iguana has the power of considerably changing its hues; but these changes are gradually performed. The colours become more dull as the period of the change of cuticle approaches—which is not, however, very frequent. Each scale has its own tint, and the colours being thus irregularly blended, an appearance is given, particularly to the younger reptiles, very much like that of worsted-work.
"These Iguanas live principally on trees, and near the windward coast of the island" (of St. Lucia). "They are not much seen, excepting in the months of February, March, and April, when they quit their hiding-places, and repair to the sea-shore or other sandy places to lay their eggs in the sand. The older females lay a great number of eggs. I have known an instance of one in confinement laying five in one day, and thirty-two within the space of ten minutes five days afterwards, making thirty-seven in all. Younger females are much less prolific, according to their size. The eggs are very liable to destruction by Ants, which fact probably accounts for their being usually deposited in sea-sand. They are soft, and without any white, and their shell resembles the most beautiful kid leather used for French gloves, of a very light straw-colour. They are about the size of those of a domestic Pigeon, but rather longer; but they vary in dimensions according to the age and size of the Iguana.
"This Iguana is not averse to water, when not too cold, taking to it only when the sun is shining; in fact, not moving about much at any other time. Its mode of swimming differs from that of other Lizards, inasmuch as it places its four legs close by the side of its body, and swims entirely with its tail. It dives with great facility, and remains sometimes for a considerable time under water. I believe that it never ventures into the sea. The tail is a very valuable limb; for, besides being the sole means of swimming possessed by the animal, it is of great use in climbing trees, although not prehensile; and it is a most important weapon of defence, a blow from it being frequently sufficient to inflict a severe wound. In fact, this reptile is rather formidable when brought to bay in the woods. It is hunted by the natives with Dogs trained for the purpose. The Dog, immediately upon scenting it, gives tongue, and, if on the ground, the Dog seizes it by the back, and either kills it or maims it, which makes its capture easy; if in a tree, the Iguana is either shaken down—a matter ordinarily of no small difficulty—or the branch is cut off. It is almost useless to attempt to find these reptiles without Dogs, as the resemblance of their colour to that of the trees which they inhabit prevents them from being easily seen. Few Dogs but those accustomed to the sport will touch them, as, in addition to the blows which they inflict with the tail, they bite and scratch furiously; and when once they lay hold of anything with their teeth, they can only be made to let go by an inducement to bite some other attractive object being offered to them. They run into holes when chased, if an opportunity offers, and when their eyes are hidden from view, they fancy that their whole body is safely covered. The flesh, particularly of the female, is a great delicacy; it is cooked in various ways, sometimes in a fricassee, with the eggs whole, sometimes roasted or stewed. The eggs have a very glutinous consistence. The flesh is said to disagree with some constitutions.
"Unless when caught young, it is very difficult to induce these reptiles to feed in confinement, and particularly when watched. Their disposition is sulky and savage, and I have known some of them," continues Lieutenant Tyler, "to die in confinement from starvation, rather than feed. This has caused me to try the following plan, which I find very successful, of affording them nourishment:—I hold them by the lower part of the body with one hand, and with the other I irritate them until they open their mouth and attempt to bite, when I insert food; and by annoying them in this way, I have not only made them eat their natural food, but I have killed some of them by forcing them to eat corn and leaves, which appear to have disagreed with them. By some of the natives this Iguana is said to eat Lizards and insects; but I have opened several, and I have never succeeded in finding any but vegetable matter in the stomach."
Of the habits of a kindred species of Iguana, the Cyclura lophura, inhabiting Jamaica, Mr. Gosse has given an elaborate description; and he tells us that the gular pouch in the Iguanidæ "is extensible, but not inflatable," as is the current opinion. Holbrook and others have remarked the same; and Professor Thomas Bell describes the fold of skin as being drawn down by a peculiar arrangement of the lingual bone, and a singular cartilage fixed to it and attached also to the skin. These parts are moved by delicate muscles, so that, when the cartilage is drawn down, the skin of course is distended, and follows it "in the same way that the silk is stretched over the whalebone of an umbrella." "In fact the skin," writes Professor Holbrook, "when distended in life by the animal, does not resemble the inflated vocal sacs of the Frogs and Toads, which are round, but looks like a fold of the skin, pinched and drawn down, the two portions of it being in contact, like a dew-lap." It appears that the Cyclura, also, is exclusively herbivorous; and Mr. Gosse remarks upon the severe wounds which it inflicts upon Dogs with its sharply-serrated tail. In general, the larger species of this family are solely vegetable-feeders, while the smaller kinds (such as the Anoles) are more or less insectivorous; and there are some, of intermediate size, which even prey occasionally upon the kindred Anoles and other small animals. The genera of these reptiles are exceedingly numerous, as we have seen, and amongst so many there must be considerable variety in the habits; but we can only notice a very few of them. Within the limited area of the small archipelago of the Gallapagos, situated on the equator about ten degrees west of South America, there are two remarkable species of Iguanidæ, of which the habits have been described and commented upon by Mr. Darwin in his volume of the "Voyage of H.M.S. Beagle." One of them is particularly so, because, as that naturalist observes, it is the only existing Saurian which can properly be said to be a maritime animal. In the whole of that group of islands, as he tells us, there is only one rill of fresh water that reaches the coast; yet this reptile frequents the sea-beaches, and no other parts of the islands. He adds that it is the only known existing Lizard that feeds exclusively on aquatic productions. Although he refers both species to the genus Amblyrhynchus, the aquatic sort now constitutes the genus Oreocephalus of Dr. Gray, and it bears the name of O. cristatus. This Lizard, according to Mr. Darwin, "is extremely common on all the islands throughout the archipelago of the Gallapagos. It lives exclusively on the rocky sea-beaches, and is never found—at least, I never saw one—even ten yards inshore. It is a hideous-looking creature, of a dirty black colour, stupid and sluggish in its movements. The usual length of a full-grown one is about a yard, but there are some even four feet long. I have seen a large one which weighed twenty pounds. On the island of Albemarle they seem to grow to a greater size than on any other. These Lizards were occasionally seen some hundred yards from the shore swimming about; and Captain Colnett, in his 'Voyage,' says, 'they go out to sea in shoals to fish.' With respect to the object, I believe that he is mistaken; but the fact stated on so good an authority cannot be doubted. When in the water the animal swims with perfect ease and quickness, by a serpentine movement of its body and flattened tail—the legs, during this time, being motionless and closely collapsed on its sides. A seaman on board sank one, with a heavy weight attached to it, thinking thus to kill it directly; but when an hour afterwards he drew up the line, the Lizard was quite active. Their limbs and strong claws are admirably adapted for crawling over the rugged and fissured masses of lava which everywhere there form the coast. In such situations, a group of six or seven of these ugly reptiles may oftentimes be seen on the black rocks, a few feet above the surf, basking in the sun with outstretched legs. I opened the stomachs of several," continues Mr. Darwin, "and in each case found it largely distended with minced sea-weed of that kind which grows in thin foliaceous expansions of a bright green or dull red colour. I do not recollect having observed this sea-weed in any quantity on the tidal rocks; and I have reason to believe that it grows at the bottom of the sea, at some little distance from the coast. If such is the case, the object of these animals occasionally going out to sea is explained. The stomach contained nothing but the sea-weed. Mr. Bynoe, however, found a piece of a Crab in one; but this might have got in accidentally. The intestines were large, as in other herbivorous animals."
The food of this Lizard, equally with its compressed form of tail, and the certain fact of its having been seen voluntarily swimming out at sea, absolutely prove its aquatic habits; nevertheless, as we are told by Mr. Darwin, "there is in this respect one strange anomaly, namely, that when frightened it will not enter the water. From this cause, it is easy to drive these Lizards down to any little point overhanging the sea, where they will sooner allow a person to catch hold of their tail than jump into the water. They do not seem to have any notion of biting; but when much frightened they squirt a drop of fluid from each nostril. One day I carried one to a deep pool left by the retiring tide, and threw it in several times as far as I was able. It invariably returned in a direct line to the spot where I stood. It swam near the bottom, with a very graceful and rapid movement, and occasionally aided itself over the uneven ground with its feet. As soon as it arrived near the margin, but still being under water, it either tried to conceal itself in the tufts of sea-weed, or it entered some crevice. When it thought the danger was passed, it crawled out on the dry rocks, and shuffled away as quickly as it could. I several times caught this same Lizard by driving it down to a point, and though possessed of such perfect powers of diving and swimming, nothing would induce it to enter the water; and as often as I threw it in, it returned in the manner above described. Perhaps this singular piece of apparent stupidity may be accounted for by the circumstance that this reptile has no enemy whatever on shore, whereas at sea it must often fall a prey to the numerous Sharks. Hence, probably urged by a fixed and hereditary instinct that the shore is its place of safety, whatever the emergency may be, it there takes refuge. I asked several of the inhabitants if they knew where it laid its eggs: they said, that although well acquainted with the eggs of the other kind, they had not the least knowledge of the manner in which this species is propagated—a fact, considering how common an animal this Lizard is, not a little extraordinary. During our visit (in October) I saw extremely few small individuals of this species, and none I should think under a year old. From this circumstance it seems probable that the breeding season had not commenced."
The terrene species, Amblycephalus subcristatus, unlike the aquatic one, is confined to the central islands of the Gallapagos archipelago, where they inhabit both the higher and damp, as well as the lower and sterile parts; but in the latter they are much more numerous. "I cannot give a more forcible proof of their numbers," relates Mr. Darwin, "than by stating that, when we were left at James Island, we could not for some time find a spot free from their burrows on which to pitch our tent. These Lizards, like their brothers of the sea-kind, are ugly animals; and, from their low facial angle, have a singularly stupid appearance. In size, perhaps, they are a little inferior to the latter, but several of them weighed between ten and fifteen pounds each. The colour of their belly, front legs, and head (excepting the crown, which is nearly white) is a dirty yellowish orange; the back is of a brownish red, which, in the younger specimens, is darker. In their movements they are lazy and half-torpid. When not frightened, they slowly crawl along, with their tails and bellies dragging on the ground. They often stop and doze for a moment, with closed eyes, and hind legs spread out on the parched soil. These Lizards inhabit burrows; which they sometimes excavate between fragments of lava, but more generally on level patches of soft volcanic sandstone. The holes do not appear to be very deep, and they enter the ground at a small angle; so that when walking over one of these Lizard warrens, the soil is constantly giving way, much to the annoyance of the tired pedestrian. This animal, when excavating its burrows, alternately works the opposite sides of its body. One front leg for a short times scratches up the soil, and throws it towards the hind foot, which is well placed so as to heave it beyond the mouth of the hole. This side of the body being tired, the other takes up the task, and so alternately. I watched one for a long time," continues Mr. Darwin, "till half of its body was buried; I then walked up and pulled it by the tail; at this it was greatly astonished, and soon shuffled up to see what was the matter; and then stared me in the face, as much as to say, 'What made you pull my tail?' They feed by day, and do not wander far from their burrows; and, if frightened, they rush to them with a most awkward gait. Except when running downhill, they cannot move very fast; which appears chiefly owing to the lateral position of their legs. They are not at all timorous; when attentively watching any one, they curl up their tails, and raising themselves on their front legs, nod their head vertically, with a quick movement, and try to look very fierce, but in reality they are not at all so; if one just stamps the ground, down go their tails, and off they shuffle as quickly as they can. I have several times observed small fly-eating Lizards, when watching anything, nod their heads in precisely the same manner; but I do not at all know for what purpose. If the Amblyrhynchus is held, and plagued with a stick, it will bite it very severely; but I caught many by the tail, and they never tried to bite me. If two are placed on the ground, and held together, they will fight and bite each other till blood is drawn. Those individuals (and they are the greater number) which inhabit the lower country, can scarcely taste a drop of water throughout the year; but they consume much of the succulent cactus, the branches of which are occasionally broken off by the wind. I have sometimes thrown a piece to two or three when together; and it was amusing enough to see each trying to seize and carry it away in its mouth, like so many hungry Dogs with a bone. They eat very deliberately, but do not chew their food. The little birds are aware how harmless these creatures are: I have seen one of the thick-billed Finches (peculiar to the Gallapagos) picking at one end of a piece of cactus—which is in request among all the animals of the lower region—whilst a Lizard was eating at the other; and afterwards the little bird, with the utmost indifference, hopped on the back of the reptile. The stomachs of several that I opened were full of vegetable fibres and leaves of different trees, especially of a species of Acacia. In the upper region they live chiefly on the acid and astringent berries of the guayavita, under which trees I have seen these Lizards and the huge Tortoises feeding together. To obtain the acacia leaves, they crawl up the low, stunted trees; and it is not uncommon to see one, or a pair, quietly browsing, whilst seated on a branch several feet from the ground.
"The meat of these animals, when cooked, is white; and by those whose stomachs rise above all prejudices, it is relished as very good food. Humboldt has remarked, that in intertropical South America, all Lizards which inhabit dry regions are esteemed as delicacies for the table. The inhabitants of the Gallapagos say, that those inhabiting the damp region drink water, but that the others do not travel up for it from the sterile country, like the gigantic Land Tortoises. At the time of our visit, the females had within their bodies numerous large elongated eggs. These they lay in their burrows, and the inhabitants seek them for food."