tesselated rubbery bottom, the tesselations apparently acting as treads do on a tire.

"Whatever I am," Jerry sighed, "I'm non-skid." He considered a moment, then added, "I can't be an insect, then. Insects can't rely on weight to keep them rightside up, and need gripping mechanisms. Okay, insect-size is out."

Jerry extended the pad before him and cautiously leaned his weight on it, then removed it back beneath his torso and studied the earth where it had rested. There was a concavity there, corresponding to the pad. It was not especially deep.

"Well, that lets out elephant-size," he reasoned, "and most oversize forms. I must be somewhere between a mouse and a middle-sized wolf. But what am I?"

Jerry tried breathing. Nothing happened; there was no sense of dilation anywhere in his body. "Odd," he thought. "Unless I get oxygen—or whatever gases this creature breathes—through my food.... Or maybe I have air-tubes like an insect's.... No, I'd have to shift my body now and then for air circulation, and I feel no discomfort remaining still. Besides, I have flesh, and that tube arrangement only functions well in a body with an endoskeleton. Must be dependent on food intake, then. Stores its oxygen or whatever."

He extended the tesselated pad, and rubbed it cautiously against the soil. There was a dim sensation of touch in the pad. But it was subordinate to a soma-centric sense of location. His pad "knew" where it was in relation to his body, but had no great tactile capacity for his surroundings. "Well," Jerry thought, "that lets out feeling my body to determine shape or function."

As it sometimes did when he was enhosted, his mind went back to old Peters, his instructor, who had taught "Project C" to the eager young zoologists. Project Contact had been mostly devoted to giving the student an open mind on metabolism and adaptability to environment. A Learner had to be able to reason out—and quickly—the metabolism of his host. It was little use knowing a Terran life-ecology; man lives on combustibles and oxygen, the oxygen combining with combustibles to provide heat, and plants live on carbon dioxide and water and sunlight, renewing the atmospheric oxygen. So old Peters had always stressed the student's learning their Basic Combinations.

Basic Combinations prepared the student—or so the school board hoped—for a wide variety of chemical relationships between a host and its environment. The students had to know what to do to survive 

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