big, dark, glistening eyes.

All at once Mr. Chatham realized that Harry was speaking to him, still in high excitement.

"What are they, Dad?" he begged to know.

His father straightened up and shook his head puzzledly. "I don't know, Harry," he answered slowly, casting about in his memory. He seemed to remember a microphotograph of a creature like those in the book he had studied, but the name that had gone with it eluded him. He had worked as an accountant for so many years that his memory was all for figures now.

He bent over once more to immerse his eyes and mind in the green water-garden on the slide. The little creatures swam to and fro as before, growing hazy and dwindling or swelling as they swam out of the narrow focus of the lens; he gazed at those who paused in sharp definition, and saw that, although he had at first seen no visible means of propulsion, each creature bore about its head a halo of thread-like, flickering cilia that lashed the water and drew it forward, for all the world like an airplane propeller or a rapidly turning wheel.

"I know what they are!" exclaimed Henry Chatham, turning to his son with an almost boyish excitement. "They're rotifers! That means 'wheel-bearers', and they were called that because to the first scientists who saw them it looked like they swam with wheels."

Harry had got down the book and was leafing through the pages. He looked up seriously. "Here they are," he said. "Here's a picture that looks almost like the ones in our pond water."

"Let's see," said his father. They looked at the pictures and descriptions of the Rotifera; there was a good deal of concrete information on the habits and physiology of these odd and complex little animals who live their swarming lives in the shallow, stagnant waters of the Earth. It said that they were much more highly organized than Protozoa, having a discernible heart, brain, digestive system, and nervous system, and that their reproduction was by means of two sexes like that of the higher orders. Beyond that, they were a mystery; their relationship to other life-forms remained shrouded in doubt.

"You've got something interesting there," said Henry Chatham with satisfaction. "Maybe you'll find out something about them that nobody knows yet."

He was pleased when Harry spent all the rest of that Sunday afternoon peering into the microscope, watching the rotifers, and even more pleased when the boy found a pencil and paper and tried, in an amateurish way, to draw and describe what he saw in the green water-garden.

Beyond a doubt, Henry thought, here was a hobby that had captured Harry as nothing else ever had.

Mrs. Chatham was not so pleased. When her husband laid down his evening paper and went into the kitchen for a drink of water, she cornered him and hissed at him: "I told you you had no business buying Harry a thing like that! If he keeps on at this rate, he'll wear his eyes out in no time."

Henry Chatham set down his water glass and looked straight at his wife. "Sally, Harry's eyes are young and he's using them to learn with. You've never been much worried over me, using my eyes up eight hours a day, five days a week, over a blind-alley bookkeeping job."

He left her angrily silent and went back to his paper. He would lower the paper every now and then to watch Harry, in his corner of the living-room, bowed obliviously over the microscope and the secret life of the rotifers.

Once the boy glanced up from his periodic drawing and asked, with the air of one who proposes a