Jimmy Mills, age 12, of Hobart, Indiana, for his question:

How soon do baby snails get their shells?

A snail's survival depends upon the elegant shell he carries on his back, and nature makes sure that he, gets this essential piece of personal property. The shell starts to form during the embryo stage and grows as the snail grows. It is a permanent attachment and part of his body. It serves to protect him from insects and certain other enemies. But its main purpose is to provide a humid hide away, without which he would soon perish.

You can observe the early stages of a snail's shell with the help of a hand lens or good magnifying glass. Find some of the small milky white eggs left behind on the slippery trail of a parent snail. The embryos feed on the yolk and develop faster in mild, moist weather. In cool.or dry weather, you can help them along by placing them in a shady, fairly warm container with moist leaves to provide a humid atmosphere.

A well ddveloped egg is fairly transparent. With a good lens, you can see the unborn snail inside. With a .;steady hand and little patience, you may even observe the slow pulsing of the heart. And there on the tiny creature's back is a small, tissue thin flake of glassy material. This is the future shell.

At this stage, your specimen is about ready to hatch. The newly born snail is transparent, but not for long. As a rule, his first act is to eat his discarded egg case. This first meal provides lime and other essential food elements. It also makes his body opaque and he loses his see through appearance.

This tiny creature is on his own and well able to make his way in his small world. He needs plant and fungus food and knows how to find it. Even more, he needs a humid environment, and this too he knows to provide for himself. His soft., clammy skin has mucous glands that ooze secretions on his back and underside. The sole of his one long foot oozes the slime on which he slides along.

The secretions on his back harden to form his shell. New layers are added at the base. As he grows, the shell is enlarged to house his bigger body. After two years, his personal hideaway has about five graceful whorls, usually in a clockwise coil. The snail is now fully grown. The shell is completed, though he may model and remodel teeth around the base to keep out large insects.

If you study the shell of an adult snail, you may trace past events in his life. When times are bad, the shell additions are narrow ridges. Grooves that are close together and gritted with dirt were built during periods of hunger. Perhaps there were food shortages. But more likely there were droughts or cold periods. Then it was necessary for the snail to retire inside his shell and seal the opening with a papery door. The widest shell grooves are built during well fed periods of activity.