Sydney Hucklenbroich, age 15, of St. Louis, Mo., for his question:
What causes certain lizards to change color?
Most animals have permanent coloration that blends more or less with the scenery where they normally spend their lives. A few have a surprising gift for changing color for reasons of their own. Some are snakes, but the most famous of these talented turncoats are lizards called chameleons.
The true chameleon is a native lizard of Africa, India and Madagascar. His appearance is outlandish and he has a startling talent for changing his scaly skin through a range of yellows, greens and greys in a matter of minutes. The so called chameleon in our pet shops is the American anole, normally at home in the southwestern deserts. This pretty lizard can switch, while you watch, from green to brown or from brown to green.
In nature, this strange gift generally serves a purpose. The scenery varies with light and shade and other passing events and as a rule the lizard's changes keep pace with nature's variations. Most of the time he blends with his natural surroundings. But off beat switches may occur under artificial conditions.
An anole placed on a white surface in a cool, well lit room may turn dark brown. In a dark room, the chameleon turns yellow. The octopus, certain snakes and other turncoats change their colors when provoked. The strange gift, then, seems to be related to protective coloration only indirectly and aroused emotions perhaps play some part in it.
In any case, the changes are caused by light sensitive organs that trigger black globules in the animal's skin to swell or shrink. The anole has a light sensitive gland in his head. The chameleon has trigger happy nerves in his skin and eyes. Variations in direct and indirect reflected rays trigger these sensitive organs to send orders to the teeming black globules in the skin.
Globules of other colors are also present in the skin. When certain light conditions trigger the black blobs to shrink to small dots, these other colors predominate and the lizard turns green or yellow. Different light rays trigger the black blobs to swell up and mask the other colors. The lizard turns dark grey or brown.
The anole has layers of green and black globules. If his light switch gland is removed, the black blobs remain small and he becomes permanently green. The chameleon has layers of yellow, black and white globules. When the black blobs shrink, he may be colored by the yellows or by a green blend of yellow and blue light reflected from the whites. When the black blobs enlarge, the other colors axe masked and the lizard is dark grey.