gun was brought immediately. It was a small weapon, with a belt and holster. The captain took it from the holster. Watching, Billy Kasker had the impression that the weapon was made of glittering, spun glass. It had a short, heavy barrel in which tiny instruments were visible. Billy Kasker watched very closely.

"Do you know how to use it?" the captain asked.

"Oh, yes," the instructor answered.

"Is it so dangerous in there that we need a Thor gun?" Susan Sidwell said. Susan had majored in ionic chemistry and had graduated with high honors.

"No, it isn't dangerous at all," the instructor answered hastily. "The weapon is worn merely for the sake of tradition."

"No danger at all, young lady," the captain said. "Nothing to worry about. Not while you've got this, anyhow." He patted the Thor gun which the instructor was buckling to his waist.

The gates were open. The instructor in the lead, the group passed through. Billy Kasker brought up the rear. Joe Buckner was directly ahead of him.

They went first to see the wreckage of the city—shattered walls, tumbled buildings, streets with rubble still piled in them. Weeds and creeping vines grew over the broken bones of this city as if they were attempting to hide the ugly scars.

The instructor adjusted his voice to the proper tone. He had made this same speech to many graduating classes and he knew exactly what he was going to say.

"You understand, of course, that this part of the old city was almost completely destroyed in our attack of the year 4021 After Yevbro, or the year 1967, according to the way the natives reckoned time on this planet. This part of it has been allowed to remain the way our ships left it, as an example of the effectiveness of our weapons."

His voice gave the impression that he was personally participating in that attack and was enjoying the destruction that had taken place. He stood straight, squared his shoulders and breathed deeply.

"What happened to the natives who lived here?" Billy Kasker asked.

The instructor frowned. "Oh, they were killed." At first he was a little irritated at the question, then again satisfaction came back into his voice.

"They got what was coming to them for trying to resist our sky ships," Joe Buckner said.

"Oh, yes, they deserved their fate." The instructor hitched the Thor gun a little higher on his hip.

Billy Kasker was silent.

"We will go next to the fields, then to the factory section—such of as there is—then to that part of the city which we have allowed the natives to rebuild. Come."

The class moved out of the city. Here they saw their first natives. Clad mostly in rags—many of them bent and stooped, some of them showing the marks of hunger—they were a quiet people who kept strictly out of the way of the class group. But except for the clothing and the marks of hunger, they were identical in appearance with their conquerors.

"Why, they look just like us!" Joe Buckner said indignantly. He sounded outraged at the resemblance.

"There are many differences," the instructor said quickly. "Note their clothing, how poorly made it is. They make it themselves out of the wool of some kind of animal—deer, I believe, or bear."

"Sheep," Billy Kasker corrected.

"Oh, yes, sheep is the name of the animal. Thank you, Billy."

"You're welcome, sir."

"But they oughtn't to look like us!" Joe Buckner continued.

"There are chemical differences," Susan Sidwell said. "Once, in the laboratory, we analyzed their blood. The color was different for one thing. They also have a much different metabolism."

"But suppose one of them escaped from the museum and got into our part of the world. How would we know he wasn't one of us, if he put on our clothes?" Joe Buckner sounded outraged.

"That is one purpose our bracelets serve," the instructor answered. "A very good question, Joe. As you know, each of us receives a bracelet at birth, which