Oliver A. Pollard, III, age 10, of Petersbury, Virginia, for his question:

What is an exoskeleton?

A whale sized insect invader from outer space is downright impossible. His exoskeleton could not hold his body together. Our insects are about as big as insects can get because they have no bony skeletons. A larger animal needs a sturdy internal skeleton as a framework to support the soft parts of his body. In biology, "exo" means "outside" and an exoskeleton is on the outside of a body.

The exoskeleton of an insect is a tough outer covering, strong enough to hold his small internal organs in their places. Its joints are bands of softer, bendable material. The two ends of each muscle are attached inside, one on each side of a pliable band in the exoskeleton. Crabs have exoskeletons of crusty material. But a turtle shell does not rate as an exoskeleton because this animal has a bony internal skeleton.