Darci Miller, age 9, of Visalia, Calif., for her question:
CAN FROGS HEAR?
Some types of frogs change their skin colors with the changes in humidity, light and temperature. Frogs shed the outer layer of their skins many times each year. Using their forelegs, the frogs pull the old skin off over their heads just as boys and girls would pull off tee shirts. Frogs usually eat the old skin as it is pulled off the body.
Scientists tell us that frogs first appeared on earth about 180 million years ago. There are more than 2,000 species of frogs and toads today that have developed from the early ancestors. They live on every continent except Antarctica and are classified as amphibians.
Frogs have rather good vision which helps them avoid their enemies and also aids them when it is time to capture food. The eyes bulge out, enabling the animal to see in almost all directions.
A frog can close his eyes by pulling the eyeballs deeper into their sockets. This action closes the upper and lower eyelids. Most species of frogs also have a thin, partly clear inner eyelid attached to the bottom lid. This inner eyelid, called the nictitating membrane, allows the frog to protect his eyes without completely cutting off his vision.
Behind each eye of most frogs there is a large disk which aids in hearing. The disks are actually eardrums. Sound waves cause the eardrums to vibrate. The vibrations then travel to the frog's inner ear, which is connected by nerves to the hearing centers of the brain.
A frog's hearing is good enough to warn of approaching trouble or the arrival of food.
Most frogs also have delicate senses of touch. This sense is particularly well developed in species that live in water. A frog's tongue and mouth have many taste buds and frogs often spit out bad tasting food. Frogs have a sense of smell that varies from species to species in effectiveness. Some, and mainly those who hunt at night or live underground, have extremely good senses of smell.
Most frogs have voices which they use mainly to call females during mating season. In some species, the females also have voices. But the female's voice is not nearly so loud as the male's.
A frog makes his sound by means of his vocal cords. The cords are made up of thin bands of tissue in the larynx, which lies between the mouth and the lungs. When a frog forces air from his lungs, the cords vibrate and give off the sound.
Some species of frogs have vocal sacs, which swell to great size while calls are being made. Species with vocal sacs produce much louder calls than do frogs that have no sacs.