Garland Condrey, age 13, of Chesterfield, Virginia, for his question:

How does a one celled animal move around?

We share our wonderful world with a vast assortment of one celled animals. Most of them are too small to be seen without the help of a magnifying lens. But various types are as different from each other as lobsters and tigers. Each type has its own ways of coping with life.

Biologists have classified about 20,000 one celled animals. Each is a protozoan of the phylum Protozoa, a scientific term meaning "first life." The assorted protozoa are certainly the world's smallest and simplest animals and most likely some of their ancestors were among the first animals to live upon the earth. More than two billion years ago, some of these remote ancestors lived in the ancient fresh water seas. And most of their small descendants still prefer life in the water. A few manage to make a living in the moisture of soggy soil. Others live as parasites in the juicy tissues of living plants and animals.

It is, of course, much easier for such small bodies to move in water than on dry land. They can depend on the fluid moisture to support their small bodies and float them, if necessary, from plare,to place,.. One celled animals, however, prefer to have some control over their traveling plans. The assorted varieties have developed different methods of navigating themselves, at least to some extent.

Biologists separate the teeming prctozoa into four main groups. The flagellates have whip like tails attached to their one celled bodies. Most of these protozoa are oval shaped and some contain green chlorophyll like the plants. Alone flagellate lashes his whip tail to propel himself through the water and to change direction in search of food: Some flagellates mass in ball shaped colonies and navigate by waving their tails like teams. of rowers.

The ciliate protozoa sprout small hairs called "cilia." Their bodies often resemble horns and other fancy shapes. The fine little cilia can be moved to fan them along in search of food. One cone shaped type also uses its hairy cilia to wave food down its funnel. Members of the sporozoa group are parasites. Some use cilia, some use flagella to navigate through the moist cells of their host plants and animals. Others are soft blobs that flow through the host's tissues by changing their shapes like living inkblots.

The sarcodina protozoa come in a wide variety. Some have delicate little skeletons, some live inside dainty shells and others are shapeless blobs. This assorted group makes uee of each method of protozoa navigation. There are flagellates with whip lash tails, ciliates with waving cilia and jellified blobs that flow and float themselves along by changing their bodies from one shape to another.

One of the most interesting protozoan travelers is the well known amoeba. Its single celled body is a miniature blob of jellylike protoplasm. The soft blob is encased in a thin cell wall through which it exchanges substances with its surroundings. The amoeba pokes a pseudopod, or "false foot," of pliable skin in any direction it chooses to travel. The soft stuffing of protoplasm streams in to swell the pseudopod and the whole cell flows one step forward. Then one or more pseudopods are extended to take the next step and the amoeba continues to move in that direction.