Walls and McNiel looked. Not far from Berry's foot, two millipedes writhed, entangled, on the detritus. It was hard to tell how long the creatures were or where one ended and the other began. They had purplish brown segmented bodies as big around as a man's thumb and scores of rippling orange legs.

"Prehistoric monsters going at it tooth and nail," Berry said grandly, "in a battle to the finish."

Walls shook his head. "No. They're making baby millipedes."

"First you're an expert on physics and now you know all about bugs. Where'd you get so educated, Walls?"

"Look at 'em. What else could they be doing?"

"Trying to kill and eat one another."

Walls shook his head again. "They're plant-eaters. That much I do know."

"You'd know it, too," McNiel told Berry, "if you weren't always jerking off in briefings."

"Get stuffed, Mac."

"Even the big ones are plant-eaters," said Walls. "Can you imagine a millipede as long as a cow?"

Berry snorted derisively. "You believe that stuff? You ever seen one that big? You, Mac?"

"No, but they say they're around."

Berry laughed outright at that. "Those scientists started that rumor just to keep us poor ignorant sailors from tracking up their precious swamp."

McNiel made a shushing sound. "It's kind of fascinating," he said in a low voice. "So that's what sex is. I almost forgot, it's been such a long time."

"What're you whispering for?"

"How'd you like someone yelling when you're having sex? I'm glad somebody around here's getting a little."

"Christ," Berry said, "even the goddamn bugs here have more fun than us." He reached down suddenly, scooped up a flat rock in his left hand, and held it menacingly over the oblivious millipedes.

"Hey," said Walls, "don't do that."

"Hell, Walls, they're only bugs."

"Just the same, don't."

"What's the matter, you scared of that butterfly effect?"

"Maybe."

"Well, I say it's a load of crap. Those scientists probably started killing and cutting up everything they could get their hands on the minute they came through the hole. Suits or no suits. They sure's hell started sometime. They've been doing it for years now, and it hasn't made a damn bit of difference in the twenty-first century. Not one damn bit."

Walls shrugged. "Not that we know of, anyway."

"What's that supposed to mean?"

Walls straightened and folded his arms across his chest. "Just a thought I had. What if--what if every time they kill a trilobite, or dig up some puny little plant, or scoop up another sample of plankton, they do change history? I mean, every time. For every single little premature death they cause here in the Silurian, the future becomes something other than what it was. And how would we ever know?"

"We'd go back," Berry said, "and see how different everything was."

"No. We'd go back, and everything would seem perfectly normal to us. We're from the future that's always being changed. We're inseparably part of it, so, if it changes, we change right along with it. Moment to moment, on and on. Who knows, the first people to come through the hole might not've been human beings at all. They might've been the intelligent descendants of--of raccoons, or squirrels, until something happened here in the Silurian that took raccoons and squirrels out of the running. Originally, there might not've been apes to give rise to human beings. Then something happened to change that. Or maybe the changes are a lot more subtle. Mac, instead of joining the Navy, you suddenly find yourself farming back in Kansas."

"You're beginning to creep me out," McNiel said.

"Maybe," Walls said, "maybe I never meet a certain girl back in Houston, so I can't very well marry her, and she and I can't very well have a baby. Maybe I marry somebody else, or don't get married at all. Maybe I don't even get born." He smiled at Berry. "What could your life become if you drop that rock?"

"What an utter load of crap!" Berry said, but the hand holding the rock wavered.

"Go ahead and do it if you're going to."

"Aah." Berry lowered the rock. "This is stupid."

"Come on, Berry, let's go." McNiel gave him a comradely slap on the arm. "Haven't eaten since breakfast, and I'm getting real hungry."

"Me, too," said Walls.

"Yeah. Me, too." Berry weighed the rock in his hand, then cast it aside. It clattered along the limestone shelf. They saw it go over the edge and heard it land wetly in the basin.

"Ah, God," Walls said in a hushed voice, "now you've done it!"

"What?"

Walls peered intently at Berry, drew back with a perplexed expression on his face, and looked significantly at McNiel. A frown slowly creased McNiel's forehead.

"Well?" Berry demanded. He looked from Walls to McNiel and back to Walls. There was the faintest note of unease in his voice when he spoke again. "What is it?"

They continued to stare at him for several seconds. Then Walls cleared his throat, grimacing as though it hurt to do so or as though he did not want to say what he was about to say, and solemnly asked, "Berry, weren't you a raccoon just a minute ago?"

For the space of a heartbeat the only sound was a gentle splash of water from below. Then Berry closed his mouth with an audible click of back teeth and lunged at his two shipmates as they retreated laughing across the shelf.

"You assholes! Assholes!"

"That look in your eyes," Walls gasped, "that quaver in your voice--"

All of them were still too full of beer for sustained running about. They collapsed onto the limestone. They caught their breath.

Berry glared hard and said, "Very funny. Ha, ha. Assholes."

Walls grinned, looked around at the coolers, sighed. "We better get going. On the count of three, everybody. One. Two. Three."

Neither Berry nor McNiel moved, or even tried.

"But, fellows," Walls said, "we've still got--" he glanced at his watch "--forty hours and thirty-seven minutes of liberty left, and, ooh la--" he kissed his fingertips "--Stinktown by night!"

McNiel laughed. Berry tried not to laugh but laughed anyway. It was sharp, bitter, and short-lived, but it was laughter nonetheless.