Popular Science Monthly/Volume 6/March 1875/Chameleons-Their Habits and Color-Changes
|CHAMELEONS—THEIR HABITS AND COLOR-CHANGES.|
IN consequence of the incredible stories anciently told of the chameleon, one is hardly disposed to regard that animal as a reality; it appears to find its proper place in mythology rather than in natural history—among fabled dragons, centaurs, and griffins, rather than among the actualities of the animal kingdom. The chameleon, however, has a real existence; and, after fiction and fable are brushed aside, a very curious creature indeed remains. It belongs to the Saurian order (lizards). The genus Chamæleo embraces about twenty species, none of them American. With one exception, the common chameleon, which is naturalized in Southern Spain and in Sicily, these animals are found only in the warmer parts of Africa and Asia. The chameleon is from ten to fifteen inches in length, whereof one-half is represented by the prehensile tail. The body is roughly pyramidal in shape; the skin is covered with papillous elevations instead of scales, and these, in some of the species, assume the shape of spiny processes along the ridge of the back and the median line of the chest and belly. The toes, five in number, are divided into two opposable sets of two and three, the toes of each set being webbed down to the claws, which are long and sharp. The head is angular, rising into a pyramidal occiput. The eyeball is very large, protruding, covered with a single lid, which has a minute aperture in the centre for the very small pupil. There is no external ear. The tongue is extensible to the length of half the total length of the animal, that is, from five to seven inches. The lungs are large, and connect with air-cells underlying the skin. The neck is so short as to prevent the head being turned from side to side. Though the chameleon is arboreal in
its habits, it is very slow in its movements. It is unprovided with any weapons of defense against its enemies. The female lays about thirty eggs, which are deposited in a hollow in the ground, and covered with loose earth.
The immobility of the chameleon distinguishes it markedly from the rest of the lizard tribe, which are generally active and quick in their movements. Alfred Brehm, who received as a present from the African explorer, Schweinfurth, a number of these animals, states that the chameleon never moves at all except from necessity; it will remain in one position on a branch or twig for hours at a time, firmly grasping with tail and paws the object on which it is perched. The eyes, on the contrary, are nearly always in motion. The chameleons sent to Brehm reached their destination in indifferent condition, the skin dry and flabby, and the animals utterly apathetic. Water having been showered upon them in fine spray, they began to recover, and to lick the drops from one another's backs; their skin assumed a better color, and soon they were clambering up and down the branches which stood in their cage, and even engaging in combat. In their battles they use their teeth, but without doing serious injury; and they have a curious way of solemnly lashing one another with their tails. But such activity as this is exceptional in the chameleon: it is to be seen especially in the pairing season. When preying on winged insects, the chameleon is seen occasionally to protrude the knobbed end of his tongue, and in an instant that member is shot forth and again retracted, bearing the prey into the captor's mouth. The extremity of the tongue exudes a sticky substance on which the prey is caught. When flies and other winged insects are not to be had, the chameleon's swivel-eyes scan the trunk of the tree, and the branches above, below, and on all sides around, to see if any creeping thing may be caught. If any such creature is approaching the spot where the chameleon is lying, he waits till it comes within striking distance, and then "discharges" his tongue at it. But, if the creature is traveling away from him, he pursues, though with grave deliberation. If the prey comes very near to his muzzle, the chameleon retreats a little, to increase the distance, and then darts out his tongue. In performing this act, the chameleon displays very great activity; otherwise, all his movements are the reverse of precipitate. Thus, if he would change from his normal position of absolute quietude—his belly resting on an horizontal branch, which he grasps as firmly as he can with all five hands (for his tail is a fifth hand)—he first advances one of the fore-paws one step; then the tail is relaxed, advanced an equal distance, and again coiled tight; next the other feet are advanced a step, one after another; and so on. It is not easy to recognize the propriety of the name little lion (chamæelon) given to this reptilian tardigrade by the ancient Greeks. And the animal is as harmless as it is slow of movement, though the ancients supposed that in the dog-days it assumes some of the lion's ferocity.
The large, projecting eyeballs of the chameleon are capable of a great variety of movements; and, what is very curious, each of them may, and usually does, act independently of the other. This circumstance compensates for the fixedness of the head, enabling the animal to direct its glances on all sides, without the necessity of calling into play any muscles save those of the eyeball. Still, when about to strike, the chameleon brings both of its eyes to bear upon the object. "Notwithstanding," says Weissenbaum, "the strictly symmetrical construction of the chameleon as to its two halves, the eyes move independently of each other, and convey different impressions to the different centres of perception: the consequence is that, when the animal is agitated, its movements appear like those of two animals glued together. Each half wishes to move its own way, and there is no concert of action. The chameleon, therefore, is not able to swim like other animals; it is so frightened when put into water that the faculty of concentration is lost, and it tumbles about as if in a state of intoxication. Nay, more, the chameleon may be asleep on one side and awake on the other."
The chameleon is often seen to inhale air, gulp after gulp, with great avidity, thus inflating its body enormously, even to the feet and tail. As has been already stated, the animal's lungs are very large—so large, indeed, that it was supposed by Pliny (who simply transcribes the accounts given by Greek authors) that the lungs almost filled the entire cavity of the body; these lungs connect with the air-cells beneath the skin. By taking air into the lungs, whence it passes into the air-cells, the chameleon is able to inflate itself to as much as twice its ordinary size; and often it remains so inflated for a long time, now slightly collapsing, again swelling out, till the skin becomes as tense as the head of a drum. No doubt it was this power of self-inflation which led the ancients to suppose that, "alone among animals, the chameleon neither eats nor drinks, its only sustenance being air."—(Pliny.)
But the color-changes of the chameleon form perhaps the most interesting phenomenon connected with this animal. We need not repeat the fabulous stories told about these color-changes: the facts which can be strictly verified by direct observation are wonderful enough without the adornments of imagination. These changes of color range from whity-yellow, through yellow, bright and dark green, to dull black; and these diversities of coloration may affect the entire surface of the animal, or one or other of its sides, or may appear only in spots. When the chameleon is asleep, and not exposed to the direct rays of the sun, its color is a whity-yellow; when basking in the sun, it is a dingy black or dusky brown. On being aroused from sleep, the side which is first awakened assumes a darker shade. There is reason for believing that sunlight, apart from the warmth which accompanies it, is very grateful to the chameleon, and, in response to this stimulus, he at once begins his play of color. M. Paul Bert, a French savant, whose name is familiar to the readers of The Popular Science Monthly, has for some time been engaged in studying the anatomy and mechanism of these phenomena. His researches are not yet completed, but we may state some of the facts which he has established.
In the skin of the chameleon he finds a close net-work of minute ducts, connecting with pigment-vesicles situated on its under surface. When the coloring-liquid is all retained in these vesicles, the animal's skin appears yellowish, that being the color of the semi-transparent epidermis. When the liquid is injected into the ducts, the color of the animal changes, the tint depending on the degree of tension in the ducts. If a nerve be cut, the region of the chameleon's body to which that nerve was distributed becomes at once a deep black, and no more color-changes occur over that area. If a piece of the skin be placed under a microscope, it will appear black. Pass a current of electricity through it, and there will be seen white vacuoles, which coalesce into irregularly-shaped masses, and these in turn break up into minute vacuoles again, leaving the field of a greenish color. Stop the current, and the reverse order of phenomena appears. M. Bert finds that the effect of curare on the chameleon is to give it a very dark color, while chloroform, on the contrary, lightens the tint; but when given in quantity sufficient to destroy the animal's life, chloroform darkens the color. Bert is disposed to believe that the chameleon possesses a special set of "color-nerves" distinct from the motor and sensory systems, and that these nerves are under the control of the will.