David Frame, age 11, of Duluth, Minnesota, for his question:

Is it true that some mammals really lay eggs?

This amazing nature story is true, though 175 years ago hardly anybody believed it. A visitor to Australia showed the scientists of Europe a preserved specimen and other reliques of the duckbill platypus. The learned scholars suspected that the specimen was assembled from various parts of other animals. All of them refused to believe in the strange mammal, especially when told that the female lays eggs.

Perhaps we cannot blame the experts who pooh poohed the notion that the platypus really exists. After all, he does seem to be assembled from pieces that rightfully belong to other animals. His bill seems to have been borrowed from a duck, his tail and furry coat from a beaver. His feet are webbed and there is a poisoned claw on each hind foot. His inner ears are covered with fur, like those of a seal. His. bones reminded the experts of those that belong to reptiles.

Maybe it would have been possible to accept these features as possible, except for one item. Reports from his native Australia claimed that the platypus hatches from an egg. Those experts of 175 years ago were positive that this was ridiculous. They knew, or thought they knew, beyond a shadow of doubt that all the furry mammals bear live babies and feed them on mother's milk. This is what qualifies them as mammals.

However, tire platypus reports kept coming, in and obviously they needed clarifying. In 1884, a young naturalist went off.to Australia to study the impossible oddity in his native habitat. And of all things, he found abundant evidence to prove beyond doubt that the impossible creature exists    and is, indeed, an egg laying mammal. The experts at home were dumbfounded. But still another surprise was waiting.

The very day after the platypus proof was found; another naturalist discovered an odd Australian animal called the echidna. This little roly poly had a long snout and porcupine quills. Unlike the platypus, he shunned the water and renounced crayfish for a diet of ants. However, the echidna and the platypus both proved to be egg laying mammals.

Detailed investigations revealed that these Australian animals have only one body opening to eliminate solid and liquid wastes and also lay their eggs. This was known to be a feature of reptiles and certain other animals. But among mammals it was unique. For this reason the platypus and the echidna were classed as monotreme mammals, a term that refers to their single body opening.

A female monotreme could never be classed as a mammal unless her babes were fed on mother's milk. However, she does not have the usual milk faucets. The eggs are brooded close to her warm, furry body. When the infants emerge, they are fed on milk that oozes from small openings on the mother's stomach. This feature is their indisputable claim to the sophisticated mammal clan.