But if we do not know the why, the how of these fluctuations of color is well understood, and is briefly stated by Prof. Pycraft:
"The horny outermost layer of the skin is colorless; in the layer beneath this are embedded iridescent cells with striated surfaces. Below this, in the deepest layer of the skin, cutis, are a large number of cells filled with refractive granules, chiefly guanin crystals. These cause white color by diffuse reflection of direct light. Nearer the surface are cells filled with oil drops, and these give a yellow color. In the granular mass are embedded numerous color-bearing granular sacs or chromatophores, containing for the most part blackish brown or reddish pigment. The branches of these sacs being contractile, the contained granules of color are drawn away from or toward the surface of the skin, and thus, combining with the stationary color, effect a corresponding change in the coloration of the animal."
The chameleons are an African family, but a few of the fifty or so species belong also to the western coast of India and Ceylon, and one is a resident of southern Spain. They vary in size from that of a mouse to a species in Madagascar two feet long.
The lizards and snakes are the most recent developments of the reptilian line of vertebrate evolution. No undoubted lizard remains have been discovered antedating the end of the Cretaceous epoch; and no fossil evidences of snakes are much older than the mid-Tertiary, yet these are surprisingly similar to existing forms. The affinities of both groups seem to be with Pythonomorpha.
[CHAPTER XXI]
SERPENTS, GOOD AND BAD
Snakes (Ophidia) are the newest and most flourishing branch on the reptilian family tree, whose trunk and lower limbs are dead or dying. They differ from lizards mainly in their elongated and limbless form (which, however, had been foreshadowed by certain lizards) and more particularly in the formation of the mouth. Instead of a solid union of the bones of the skull, many of the bones, especially about the mouth, are connected by an elastic ligament, allowing the snakes to open their mouths widely enough to swallow larger prey than otherwise would be possible. The palatal bones, as well as the jaws, bear small, solid, recurved and pointed teeth, replaced by others from the same root pulp when lost; they have little chewing power, but are useful to seize and hold food which is then slowly swallowed by the snake gradually working its jaws ahead and over the object, until the muscles of the throat can grip it and slowly work it downward into the tubelike stomach. Serpents strive to turn their prey and swallow it headfirst.
The tongue in all serpents is a slender, extensible organ, forked at the tip, usually black, and always seen protruded and waving about when a snake is disturbed. Uninformed people call it a "stinger," but it is merely the animal's tongue and used as such. It serves the additional purpose of an instrument of investigation, the serpent informing itself by touching with its tongue as to the nature of many things with which it comes in contact. It has, however, no stinging or other harmful purpose or power whatever. A rattlesnake's tongue would harm you no more than one of the little love licks that you get from your favorite puppy.
The eyes, which may be rudimentary in the burrowing species, or large in those of nocturnal habits, have no eyelids, and are covered with a transparent film of skin that is sloughed off whenever the skin is shed, which happens frequently in young, growing individuals, but only annually in adults, as a rule; and for a day or two snakes are blinded by the loosening of this covering. No snake has ear openings, and their hearing is dull. The sense of smell, however, is well developed, and it is probable that these animals obtain much food by its aid, even following a trail by the nose.