David James, age 12, of Greenbrier, Tennessee, for his question:

How can earthworms breathe underground?

A small fellow such as the earthworm must live a rather limited life. He cannot travel far or move around as well as the larger animals. But smallness sometimes has its advantages. The earthworm can make a comfortable world for himself in a small corner of a field and find everything he needs there in the soil. We may find these limited conditions hard to imagine. The ground to us seems hard and solid, but to the earthworm it is a mass of loose, crumbly dirt filled with pockets of usable air. And quiet Mr. Pinky does not need lungs or a nose to breathe in and out.

His entire skin can absorb oxygen from the air by a process of diffusion. As he burrows below ground, he absorbs oxygen from every tiny pocket of air that touches his body. There is, however, a snag in this neat breathing system. The worm's skin must be moist in order to dissolve and diffuse oxygen. The little fellow cannot allow his body to dry out. He tries to keep moist with secretions that ooze from glands in his skin. But he always burrows deep in the dirt to escape the heat of the daytime sun and in hot weather he seals his burrow with a plug of soil.