Debbie Baker, age 12, of Wickenburg, Ariz., for her question:

HOW DOES A SNAIL LEAVE A TRAIL?

Snails make up a large family of creatures classified in the (ital) gastropod (unitall group. You can find them in fresh and sea water, along the marshes, and in most damp and shady garden areas. Some even live in trees.

With the single exception of the slug, all snails wear a spiral shell and travel by means of a broad, muscular foot that extends from the shell.

Moisture is very important to him. To conserve moisture, the snail retires within the shell and closes the opening with his flat foot, sealing the edges with a mucous like secretion.

The snail also uses the same secretion to smooth his travel course. Below his mouth is a pedal organ that secretes a slime track.  A slug, which has no shell for protection, uses the same secretion to lubricate and protect his tough body as he travels.

Below the shell of the snail the head and foot are joined together. The head bears retractable tentacles, the tips of which have eyes with corneas, lens and retinas. They also have an organ for smell.

Sea mollusks  a type of snail  have gills while the fresh water snails have both gills and lungs. The land sn4ils have lungs and a network of blood vessels in the mantle around the cavity of the shell. Air enters and leaves by a respiratory pore. A single kidney discharges into the mantle cavity and drains blood from the cavity around the heart.  The heart has a single ventricle and auricle. The digestive system consists of the mouth, pharynx with a jaw and radula used for tearing off bits of food, a thin esophagus, a crop, stomach, coiled intestine and anus. Salivary glands secrete through ducts into the pharynx and the liver, located high in the shell, secretes into the stomach.