Matt Bonham, age 11, of Eugene, Oregon, for his question:

Do more animals live on land or in the sea?

A good question always leads us by the nose into new and fascinating realms. Sometimes the answer is not known in complete detail. Such mysteries are intriguing. Sometimes .a large question spreads over two or more topics. For example, today's question could mean the number of individual animals or the number of species.

There are two ways to tackle today's subject. One approach is to count the individual animals of the land and .sea one by one. Obviously a fantastic census project of this sort is downright impossible. However, biology statisticians often spot check small sample areas to estimate animal populations in wider regions. Such an estimate merely gives an educated guess and nobody expects it to be very accurate.

Another approach is to compare the numbers of different animal species of the land and sea. So far, a million or so species have been identified and classified  ¬and goodness knows how many more still are undiscovered. Of the 50,000 or so vertebrates, 20,000 are fishes of the sea. But most of the 5,000 mammals and 6,000 reptiles, the 1,500 amphibians and 8,600 birds belong to the land. Sponges, shellfishes and softbodied corals belong to the sea. Crustaceans and several other large groups have species that belong on land and in the sea.

At this point, you might guess that more animal species belong to the sea. After all, the ocean covers about 70 per cent of the earth. Life on land exists on or near the surface, plus the birds that make trips into the lower atmosphere. In the vast ocean, life teems in the sunlit surface    but it dwindles as it gets down to the midnight depths. Altogether, the global ocean has 300 times more living space than the land. And it seems to be a rule of nature that life must strive to exist wherever possible. But let's not be too sure about the number of land and sea species.

We can, however, be quite positive about the census taking. A census of land animals, for example counting the noses of every mouse and flea, might approach the number of stars in our Galaxy. If this is so, then the census of the sea would outnumber the stars in at least a dozen galaxies. One by one, the teeming populations of the sea far exceed land animals. However, the land has a larger variety of species.

Almost three quarters of the earth's known animal species are insects. Though certain amphibious types spend part of their life cycles in ponds and streams, the insects are rated as land animals. Their enormous variations account for the fact that more animal species live on land. Of course, a million or so strange creatures yet may be found in the mysterious sea. But some experts estimate that another million or so insects and other animals may be added to the list of land dwelling species. It looks as if the sea has more individual animals and the land has more species.