said Sam. "Your guess is as good as mine."

"But if we're the first human beings to land here—it ain't possible!"

"I know that. But there he is."

At the sound of their voices, the dog broke into a series of furious barks, backing away as it did so.

"What kind is he, Pop?"

"He looks like a mongrel to me. A bad-tempered, medium-sized mongrel with an ugly look about him. Maybe I ought to shoot him and get it over with."

"Shoot him? Don't do that! I want him as a pet."

"He looks too wild to make much of a pet."

The dog gave one last bark of defiance, turned, and fled in the same general direction, Sam noticed, as he had run last time.

"Maybe dogs do grow on other planets, Pop."

"Only if men have brought them there."

"Then that means there was a ship here?"

"At some time or other there was a ship. I don't think it was smashed up, or I'd have seen wreckage when I cruised around before landing. That dog was either left here by mistake, or deliberately marooned."

"Maybe—maybe he's with somebody who's still here."

"Not likely," said Sam thoughtfully. "He wanders around too freely, and he seems unused to the presence of human beings. Besides, no men would be likely to live here long without shelter. And I've seen no sign of any house or hut."

"Could he belong to a being that wasn't human?"

"No," replied Sam with certainty. "Only human beings have been able to domesticate dogs. If a dog is here, a human being was once here. That's definite."

"He would make a good pet," said Mark longingly.

"Not that one. Maybe I should have got you a dog long ago. It might have been just the kind of companionship you needed. But you can't make a pet of this animal. He's been away from people too long, and he's developed some mean habits." And he added mentally, "Like me."

"I could train him," said Mark. "He wouldn't be any trouble at all, Pop. I'd train him and feed him, and he'd be just like one of us. And—and like you say, Pop, it wouldn't be so lonely for me."

Kids don't give up easily, thought Sam. All the same, he had an idea that with this dog all the persistence in the world would be useless. He shrugged, and said simply, "We'll see." And then they went into the ship to eat.

All through the meal he could tell that Mark was thinking about the dog. The boy's thoughts seemed to affect his appetite. For the first time, he left some of his proteinex on the plate.

"I'm not very hungry today," he said apologetically. "Maybe—" He looked inquiringly at his father.

"Go ahead and finish it," said Sam. "We've got plenty of food. I'll fix up something else for the dog."

"But I want to feed him myself, Pop. I want him to get used to me feeding him."

"I'll give you your chance later."

Afterwards, Sam thriftily opened an old can of a less expensive variety of proteinex and put half of it on a platter, which Mark carried outside the ship. He moved off about a hundred yards in the direction the dog had taken, and set the platter down on a rock.

"The wind is blowing the wrong way," said Sam. "Let's wait a while."

In ten minutes the wind shifted, and if the dog was near, Sam felt certain that he had picked up both their scent and that of the food. That his feeling was correct was shown by the sudden appearance of the animal, who barked again, but this time not so fiercely. And he stopped barking to sniff hungrily, at the same time keeping his distance.

"Here, mutt," called Mark.

"I'm afraid he won't come any closer while we're around," said Sam. "If you want him to have that food, you'd better go away from it."

Mark reluctantly backed away with his father. The dog approached the food, finally rushing down upon it as if he feared it would escape, and gobbled it.

In the days that followed, they continued to feed him, and the