Tom McGowan, age 11, of Malton, Ontario, Canada, for his question:

Is the platypus a reptile, fish or mammal?

Fishes and reptiles have scaly skins and both are cold blooded animals. A few fishes and reptiles bear live young, though the vast majority lay eggs. Most of them lay large numbers of eggs and leave their offspring to take their chances, with no parental assistance. The platypus is one of the oddest animals on this earth. But she is neither fish nor reptile.

True, she is fond of the water and an expert swimmer. She also lays eggs. But she is a warm blooded creature and she wears a thick coat of soft fur. That luxurious coat is sufficient to qualify her as a mammal, because no other animals have true fur. It is true that the other mammals bear live young. But the platypus feeds her newly hatched babes on mother's milk. This makes her membership in the mammal class definite.