Arthur Robins, Age 9, Of Allentown, Pa., for his question:

What happens to the water that goes into a fish's mouth?

When you watch a goldfish,, he seems to be gulping mouthfuls of water all the time, day and night. Nobody, you would think, could drink all that water. And., in fact, goldie is not drinking the water that goes into her mouth. It passes into her gills, which are under those round flaps on the sides of her head where you might think her ears should be.

The gills take oxygen from the water in much the same way that your lungs take oxygen from the air. Goldie does not send the used water back out again through her mouth. It streams out through the back of her gills. The water that goes into her mouth passes through her gills and out again to join the water in the fish tank.