Astonishingly, even though we know the number of stars in the Milky Way (10 to the 11th power), the mass of an electron (9.1 x 10 to negative 28th power grams), and the diameter of the earth (7,926 miles), we don't know how many species of organisms there are on the earth. If you collected one of every kind of plant and animal in the world, how many living things would you have? Ten million? Thirty million? No one knows for sure.

This might seem hard to believe. Most of the larger plants and animals around us are known. But other places in the world- the dense rainforests of the tropicsm, for example-have proved harder to survey. Using new inventory methods, a scientist andhis team found more than 2,500 kinds of insects on a single rainforest tree, over three-fourths of which were previously unknown.

Not all of the kinds of plants and animals coming to light are the size of insects. As recently as 1975, scientists discovered the world's largest type of wild boar in Paraguay.

Approximately 1.7 millino species-breeding groups of plants and animals-have been named to date. Yet most scientists believe that this figure does not begin to reflect the earth's diversity of life. Some place the total number of species near five million. Based on the inventory of tropical forests mentioned above, other researchers give estimages of over thirty million species. Thirty million different kinds of plants and animals.