The alien ship resembled a long jointed stick studded with budlike structures and a cluster of bubbles like white foam at one end. It was very large, as starships must be. It was not worldlike in Yggdrasil's sense, but the segmented shaft was many miles long, and each individual bubble was easily a half mile in diameter.

“It's a fusion vessel, all right, but not a ramjet,” said Jun Davd's deep, composed voice from the screen. “They carried their fuel with them. They're using a deuterium-helium three reaction. But there are traces of tritium from previous burns."

Bram saw the implications immediately. “They started their trip with a deuterium-tritium reaction. And they've been at it long enough to have to switch fuels because of the decay of their tritium."

He turned his eyes from the sticklike image on the portable viewscreen long enough to exchange glances with Jao. Jun Davd had returned to the tree in order to have the full resources of the observatory at his disposal, but the burly physicist had left Trist to hold the fort and returned to the diskworld, where, he said, “the action's going to be."

The strangers’ starship had been decelerating steadily for six days now at half a g. It had covered more than two hundred million miles since it had first been spotted approaching from the outer system. It would rendezvous with the diskworld in only a few hours—still with too much velocity, according to Trist.

Bram, waiting with Jao, had set up shop in the great sports arena, which was mostly cleared out now. A few people in casual dress moved through the empty spaces, picking over the remaining exhibits. Ame was among them, a distant figure working with a male associate to pack and label pods. Bram had sent all the junketing tourists—and everybody else who could be spared—back to the tree. He didn't want half the population milling around where they could not easily be rounded up. Not with this new development unfolding. But Ame had refused to go. “Not on your life,” she'd said. “I wouldn't miss this for anything. Besides, you're going to need me, and Jorv, and all the other experts on terrestrial life.” She was right, Bram knew. Only a few hundred people remained on the diskworld, but he had seen to it that a sprinkling of specialists in the once-abstract disciplines was included.

“Yes,” Jun Davd's voice agreed. “If they came from Sol, they've been traveling at nonrelativistic speeds. Tritium's half-life is only twelve years and a bit. At the end of their first fifty or sixty years, most of it would have turned into helium three, their secondary fuel. And what does that suggest?"

Jao's eyes glinted. “Deuterium-tritium fusion is easy. But tritium's hard to come by. They would've made it back home as a by-product of their fusion reactors. Deuterium-helium three fusion's easy, too—but first you have to accumulate enough helium three. Deuterium's more plentiful. But I guess they're not capable of deuterium-deuterium fusion yet. Nor of the boron fusion-fission reaction the Nar used in their early starships."

He glanced at the bubble-and-stick image that was being transmitted from Yggdrasil's telescopes. “So this is a very early model starship. They're in the first stages of exploration."

“It isn't an exploration ship. It's a colony ship. They don't have enough reaction mass for a return trip."

“But the bubbles..."

“If they ever were fuel tanks, they're empty now. Our radar shows they're hollow. And they haven't collapsed, as a sensible membrane envelope would, nor have they been cast off. I suspect that they've been converted into environmental pods for a very rapidly expanding population."

“They could have planned to set up reactors here to manufacture tritium,” Bram suggested. “Or mine a gas giant for helium three."

“Except that there are no gas giants in this system. Nor oceans to extract deuterium from. All they could have known about this system is that there was mass here. And energy."

Jao was agape, and Bram didn't blame him. “You mean they sent a shipload of colonists out—to travel for generations and breed aboard ship—without knowing for sure what they'd find here? They must hold their lives cheap!"

“And it must follow that they hold other lives cheap, as well,” Jun Davd said hollowly.

“Jun David, what are you driving at?” Bram demanded.

“They're closing with the disk very rapidly, and they still haven't turned off their fusion drive. They must have seen Yggdrasil. And felt our radar probing them. They know there's life here."

Trist's voice cut in, sounding harsh. “They're going to overshoot, Bram. They'll have to cut right across the rim of the diskworld."

Bram was aghast. “They'd have to assume there must be intelligent life on the surface even if they didn't care about the artifacts they'd be destroying. And they have no way of knowing exactly where on the rim we might be."

“We're sending them radio messages,” Trist said. “Just intelligent noises on every wavelength—number patterns and so forth. They don't respond. It's as if we don't exist for them."

“I can evacuate,” Bram said, thinking frantically. “No, that would take too long,’ wouldn't it, with everybody spread out? It wouldn't matter, anyway. Yggdrasil's less than twenty thousand miles away, right in the path of destruction if the drive exhaust comes anywhere near here."

“Yggdrasil's safe, and so are you, we think,” Jun Davd said. “These careless strangers will intersect the rim between moons—at least five or ten million miles from your position."

“You think,” Jao growled.

A scattered crowd had gathered on the plain, facing the point where the long straight ribbon of land vanished into infinity. About three hundred people were left on the diskworld, and virtually all of them were here in their space suits. They stood in small, chatting groups or lounged against the landing legs of the waiting shuttles. A few enterprising souls had even climbed to perches atop the spaces vehicles for a better view.

Bram was still uneasy about everybody being out in the open. His first instinct had been to keep people as far underground as possible. But Jun Davd had assured him that the alien ship was holding its course. For all practical purposes, the enormous curvature of the rim was a straight line, and even if that dreadful inferno of fusing deuterium and hydrogen three passed only marginally below the theoretical horizon, millions of miles of diskworld would be interposed between Bram's people and death.

Not so for the Cuddlies inhabiting that distant latitude. Bram's mouth tightened into a grim line as he thought of the slaughter that would take place in a few minutes.

The Cuddlies here certainly had no premonition of what was about to happen to their faraway cousins. Attracted by the festive atmosphere, they hung around the people, popping in and out of crevices and sometimes pulling at space-suit legs to be picked up.

“You could see it now if you were hanging in a bosun's chair over the outside rim,” Jun Davd's voice sounded in his ear. “It's cutting upward from below a chord drawn between you and its point of intersection. It will rise above your sunward horizon after transit."

“How soon?” Bram asked.

“Four minutes. If you sight along the outer edge, you ought to be able to see some lightening of the limb."

Bram strained his eyes. Beside him, Jao, fussing with the tripod of a theodolite, straightened for a look.

Yes, the precipice edge that faced the interstellar night had gained a silvery hairline illumination. It projected a short distance as a faint straight scratch against the darkness. Where the scratch ended would be the theoretical horizon.

“Got it?” he asked Jao.

Jao struggled with the theodolite. “Just a second. Yah. Here we go."

“One minute."

All across the pebbled plain, space-suited figures showed that they were listening in on the circuit by ceasing their activities and becoming still. The Cuddlies, sensing the humans’ absorption, froze.

“Now,” Jun Davd said.

Where the threadlike horizon narrowed to invisibility, there was a great flare. Garish light spilled over the plain, casting long black shadows. Human figures, their reflexes slower than their helmet filters, raised arms in a delayed reaction to ward off the light.

Bram saw streaks of movement through the awful glare: startled Cuddlies popping back into their holes. When his eyes adjusted, not a Cuddly was to be seen anywhere.

The light dwindled to a point and disappeared. Moments later, a bright star rose against the inward horizon.

Except that it couldn't be a star, because it was in front of one of the great, dully visible faces of a disk.

Jun Davd's voice in Bram's ear was tinged with sorrow. “The exhaust swept across one of the regions we never had a chance to send a survey team to. The one with the great elliptical bowl and the pyramidal objects rising tens of miles high on stilts. Radar echoes appeared to show a small city in the vicinity to service it, whatever it was. We thought it might be a research center of some sort."

“I remember,” Bram said.

“There's nothing there now but thousands of square miles of melted slag."

Bram thought of all the Cuddly warrens that must have lain under the complex and about all the Cuddlies outside the zone of direct destruction that would be dying of radiation sickness in the days and Tendays ahead.

Beside him, Jao swore. “I was going to come back. Maybe in a couple of hundred years when we got ourselves established and could afford to lay off a little. The pyramid installation was the first place I wanted to look at."

In the disk-filled inner sky, the artificial star seemed to slow as if it were on a rubber band. Slowly, slowly, the rim of the diskworld pulled it back.

“They're not going to bother to go into an orbit,” Jun Davd's voice said. “They're just going to hang there."

“Disposable ship,” Jao said. “Or disposable colonists."

“A life form that just sets blindly out and goes anywhere,” Jun Davd mused, “and takes root if it can. And now, I'm afraid, they're making their second pass to bring them to a halt over the rim. They don't bother to think things out in advance. They're empirical."

The star hung over the point of the horizon and winked out. Across the narrow plain, space-suited people eddied about, and groups began to break up. A few cautious Cuddlies popped up out of their holes.

“Show's over,” Bram said.

Back inside a sports arena that buzzed and echoed with excited conversation, Bram and Jao conferred with Jun Davd and watched on their portable screen the images from Yggdrasil's remote sensors.

“We were lucky,” Jun Davd's distant voice said. “One of our orbiting cameras happened to be no more than a quarter million miles from where our visitor decided to park. We've moved it closer in the last hour, and we're still closing."

People kept poking their heads into the alcove where Bram and Jao had installed themselves. It would have been hard to jam more people into the area where people were crowding around for a look at the screen. Outside, on the rocky floor of the arena, a number of people had been foresighted enough to fetch their own personal viewscreens from their quarters and slave them to Bram's circuit, and each of these had growing knots of watchers around it.

“They're continuing to ignore us,” Jun Davd said. “Not a peep on any wavelength."

Bram studied the fuzzy image. The lack of definition took away the regularities that would have labeled the ship an artificial shape and made it look like a life form. A life form with a long lumpy stem whose segments swelled where they fit into each other and a living jelly of bubbles to cap it. The nodules along the shaft fostered the notion.

For a moment Bram toyed with the idea. Yggdrasil was a living spaceship, after all. Why not this? What kind of life form would look like a budding stick, and what function would be served by the gob of bubbles at one end?

Then he dismissed the thought. The thing was a machine, after all—a relatively primitive machine that generated a howling storm of hydrogen-helium fusion and probably poisoned’ its inhabitants.

“We make it at approximately twenty miles long,” Jun Davd said. “It could alight in Yggdrasil's branches and never be noticed, but it's still an impressive achievement for a manufactured article."

“What are they doing?" Bram said.

“Nothing, as far as we can tell. No extravehicle activity, no electromagnetic emissions. No attempt to reorient the axis of the ship as a preliminary to achieving some sort of rational orbit. They just appear to be waiting."

“Waiting for what?” Jao rumbled. “They sit there like that, and eventually they're going to drift off the rim and get sucked down the side. Then they're going to have to turn on that torch of theirs and burn some more landscape."

“Perhaps they don't care,” Jun Davd said.

Bram was staring at the glob of bubbles. Overmagnification had blended them into an undifferentiated mass, but despite the bleared focus there was enough mottled shadowing for the eye to appreciate them as a clump of hundreds of separate spherules.

They were hollow, according to Jun Davd's radar echoes. Empty fuel tanks, each a couple of thousand feet in diameter—big enough to hold millions of tons of frozen hydrogen in its different isotopic forms. And there would be a complex maze of piping to skim off the helium three as it became available and store that separately, too.

Tritium was biologically hazardous. It was hard to believe that the empty bubbles had been converted into environmental pods. Jun Davd's imagination must have run away with him. Surely no people would be that reckless with their generations.

The vague mottling seemed to shift, showing one of the globules more distinctly.

“Do I see movement?” Bram said. “Or is that just image shimmer?"

Jao grabbed Bram's arm. “No, it's movement."

As they watched, one of the bubbles detached itself from the foamlike cluster and drifted free. A fine mist spouted from it.

“Chemical jets,” Jun Davd said. “They're matching velocity with the rim."

A hum of voices rose in the surrounding bay. “Hold it down,” Jao thundered.

“You were right,” Bram told Jun Davd. “They moved into their empty fuel tanks. If that one held tritium, there must still be residual radiation. They'd have to be desperate for expansion room."

“The original life-support system must have been confined to the budlike structures on the stem,” Jun Davd said. “But with the fuel tanks, they'd have a hundredfold the living space in reserve, becoming available as they spilled over."

“What kind of intelligent race,” Bram said in dismay, “would breed that unrestrainedly, with no sureties at their destination?"

Ame pushed through the surrounding press of bodies. “The longfoots,” she said. “The females had a dozen young to a litter, remember? They've come back."

“Or their successors have,” Bram said. “Whatever else the longfoots were, they were a thoughtful people. That ship doesn't look like their technology."

“Rise and fall, Bram-tsu,” Ame said defensively. “Devolution and reradiation of species."

On the screen, the separated globule fell with alarming speed toward the narrow rimscape. “That's awfully big to be using as a lander, even on a low-gravity world,” Jun Davd said. “But that's what they're doing with it."

“One mistake and they'll be scattered all over the landscape,” Jao grunted.

Bram calculated spherical volume in his head. “There could be a population of thousands in that bubble. If all of the bubbles are inhabited..."

“These strangers must like to travel in large crowds and take their environment with them,” Jun Davd said. “That detachable habitat of theirs is big enough to qualify as a self-contained colony. The ship could drop more of them off here and there around the rim and leave them to fend for themselves. Then flit around the system and seed the other disks."

“You talk as if that ship were a living organism."

Jun Davd laughed. “If the surviving colonies grow up to build more ships like it, then it fits the definition."

Trist's voice cut in. “We're getting message traffic now between the ship and the lander."

“Radio? Laser?” Jao's voice was impatient.

“Neither. They communicate by modulating polarized light—switching rapidly back and forth to different planes of polarization. We can't read the signal, but it's a signal, all right."

“What kind of pattern? Binary, or what?"

“No, it's positional. It codes for some kind of grid. And now that you know that, you know as little as I do."

“Why would they modulate polarized light?” Bram asked. “If you're going to communicate by light, there are easier ways to modulate it for a signal."

It was Ame, unexpectedly, who answered. “Perhaps because it corresponds to their natural sensory input."

“Now, Ame, we use radio mostly,” Jao said condescendingly. “But we don't see by radio waves."

“No,” she said, “but we use it the way we use visible light—by modulating its frequency. Or we use it by mimicking sound—by modulating the amplitude."

Bram pondered Ame's startling supposition. “But where does a positional grid come into it?"

“I don't know, Bram-tsu. We use radio waves to build up pictures or sound. And when we use laser, we use it more or less as if it were just an improved kind of radio. It has something to do with the way they think or perceive things."

“Trist, can you rig up something that'll modulate polarized light?” Bram asked.

“Sure, nothing to it,” came Trist's cheerful voice.

“Can you beam some of their own patterns back at them—just as a recognition signal? Just to get them to notice us."

“I'll get on it right away."

“And get somebody working on that grid."

“The chess club's already taken it on as a project. So have the linguists."

“Get them together."

On the screen, the stick ship had moved out of the frame as Jun Davd's remote camera followed the life-support module. It showed as a pale blob against a rim-scape that whizzed by at blurring speed.

“Looking for a spot to light,” Jun Davd said. “They had a choice of two directions. They chose yours."

“How long before they get here?"

“At their present velocity? About two days."

Two days later,’ the thing passed overhead, looking very large. Everybody was outside again for the passage. As it sailed by, everybody waved. A few energetic jumping jacks leaped straight up fifty feet or more, wigwagging with both hands. But the bubble took no notice. It receded into the distance, blank as an egg.

“They almost nicked one of the moonropes,” Jao said. “They're flying much too close to the rim's edge. And too low. The pilot's a bit impetuous, isn't he?"

Bram, sweating inside his helmet, hand-cranked the flywheel—mounted telescope to follow the enormous spheroid. The others crowded close to look at the photoplastic image in the visored plate at the end of the barrel.

“They're losing speed and altitude fast,” Bram said. “They're going to come down about two hundred miles farther on, it looks like. We'll have them for neighbors."

“The pilot's braking too fast,” Jao said, squinting at the shaded image. “As if he made up his mind on the spur of the moment. Whoops! He changed his mind. He's lifting up over that escarpment! Almost grazed it. He must be shaking up his passengers."

Jao's commentary may have been unjust. The huge globular object went into a long graceful glide, riding the plume of its jet, and set down with abrupt gentleness in the exact center of a flat circular feature where the plain was smooth.

“A seat-of-the-pants natural,” Bram said. “Like Lydis."

“If he wears pants,” Jao said. “Or has a seat."

Ame was looking thoughtful. “What do we do now, great-great-great-grandfather?"

Bram sighed. “I suppose we'd better pay them a visit."

Everybody wanted to go. Bram fended them off as diplomatically as possible when they came barging into the bay where he was trying to work out a plan with Ame and Jao.

“The first meeting is going to be very important,” he told them over and over. “We'll have just a few specialists, each with a job to do. We can't take a crowd along."

And then, of course, everybody tried to convince Bram that he or she was a specialist.

“As a sociometrician,” Silv Jaks said, getting strident, “my insight into the interrelationships of individuals will be invaluable."

“We don't even know if they're human, Silv,” Bram said. “What we're really after is a paleobiologlst."

After she stalked out, Jao said, “That was nothing. One of the archaeologists insisted on being included because, he said, he could tell us a lot about them by studying their pottery."

Ame wrinkled her nose. “It might not be a bad idea to take along someone from the Theoretical Anthropology group, though. It would give us some kind of benchmark for behaviors."

“Who do you suggest?” Bram said.

“Heln Dunl-mak,” Ame said promptly. “She's a sociobiologist. She worked with us to try to analyze longfoot society from physical clues. She's even been studying the behavior of social insects from the old books and holos."

“All right,” Bram said.

“And we'd better have Jorv."

Bram hesitated. “He's an awfully impulsive fellow. Establishing contact could be a delicate business."

“He knows more about terrestrial life forms and their development than anybody we've got,” Ame said. “There's his assistant, Harld, but..."

“I'll keep an eye on him,” Jao said, twisting around from his console. He winked. “With a steady hand like me to keep him in line, there won't be any trouble."

Bram said, “I thought you'd stay here and—"

“What?” Jao gave a roar of outrage. “Who's going to operate the equipment? I've rigged up a computer signboard. I've programmed it with an image library and everything."

“All right, all right,” Bram said hastily. “I wish we had a linguist."

“They've all gone back to the tree with their tons of books and micromedia in their own pet languages. What do we need a linguist for, anyway? Languages all either have a grammar more or less like Inglex, or they don't, like Chin-pin-yin. And I remember my childhood Chin-pin-yin as well as anybody. And when it comes to nonhuman speech, all us old-timers have a smattering of the Small Language.” He squinted at Bram. “And one of us, if memory serves, even has a smattering of the Great Language."

“There won't be anything like that from any kind of terrestrial stock,” Bram said.

Jao turned back to his console. “Trist's getting more radio traffic between the stick ship and that camp out yonder. Want to hear it?"

He turned up the volume, and a series of rapid, hard clicks came out of the speaker, like twenty people snapping their fingers as fast as they could.

“When did they switch from modulated polarized light to radio?” Ame asked.

“At about half a million miles. But Trist's analyzed the signals. He thinks they simply reproduce the patterns of the polarized light version—same positional code on a grid. He still hasn't figured out how the grid is organized, though. One thing's for sure—it isn't any simple up-and-down-and-across raster. Trist thinks it's irregular.” Jao looked troubled. “But that's crazy."

Bram listened to the snapping sounds for a while. “Maybe their receiving equipment is better than my ear,” he said, “but it sounds as if those noises are coming on. top of each other—overlapping. How can they extract an information-beating signal out of that?"

“Trist's taken the signals apart. He says he thinks they're organically produced."

Ame scrunched up her features. “It's a language, then. A language where sounds have visual coordinates."

“I don't understand,” Bram said.

“Bram-tsu, our group's done a lot of work on sensory impressions and perception,” Ame said. “Back during the years when we were trying to build up the new sciences. Doc Pol helped us with the medical aspects."

“That old curmudgeon!” Jao exclaimed. “I thought he didn't believe in anything he couldn't tap, prod, or take a urine sample from."

“He says polysenses are very common among human beings—much commoner than is believed. People who hear sounds as smells, for example, or who taste colors."

“Crossed wires,” Bram said.

“No, it isn't just that. It's normal in all of us to some extent."

Bram thought it over. “Like Edard reading an orchestral score and hearing the music."

“Something like that."

“Or Mim swearing that different keys have different textures—G-major being hard and brittle, D-flat soft and velvety. She had an argument with Ang about it. Ang said the only difference between keys is that they're higher or lower."

“Colors!” Jao said suddenly. “Numbers have different. colors. That's how I remember them. Equations transform the colors. I thought everybody saw numbers that way."

“Drugs will induce that kind of cross talk sometimes,” Ame said. “Your nervous system just happens to work that way naturally."

Jao grinned. “Hey, Ame, what if you see flashing lights when you bump your elbow?"

“What about it?"

“Me, I get a pain in my elbow when I see flashing lights."

Bram cut through the clowning. “So our new neighbors have a neural hookup between the sounds of their language and some sort of visual grid?"

“And they see the different planes of polarized light, don't forget that."

“What kind of eyes must they have?” he wondered.

“Nothing like ours. Or the longfoots. Or the Cuddlies. Or any other kind of mammalian life we know about.” She hesitated. “They may not have a continuous field of vision. They may see things as a mosaic."

It was a very strange thought. “What would the world look like to them?” Bram wondered aloud.

“We'll have to ask them, won't we?"

Bram turned his attention to Jao's screen. Jao was fiddling with images. He had made a sort of netlike structure out of green lines. The net kept stretching itself out of shape and changing the relationships between its warp and woof. It also kept trying to bend itself around various abstract three-dimensional shapes.

The snaps and clicks kept pouring from the loudspeaker. Bram could see that each one generated an orange dot within the distorted squares of the net. The showers of dots kept trying to arrange themselves into patterns within the ever-changing net.

“Are we still trying to get their attention on the frequency they use?” Bram asked.

“Yar, I've got a loop going on the transmitter. Trist is trying to raise their ship with the same program. Imitating their grid without knowing the coordinates is gobbledygook, but they still should extract a pattern."

Bram shook his head. “I thought they might have tried to contact us by now. The way they set down so abruptly after their flyover of our camp."

“We're keeping watch from a little way up the moonrope,” Jao said, “Some volunteers set up a telescope station on top of the stalled moon car. They'll let us know right away if anything starts moving in our direction.” He adjusted a dial. “But I don't think they're coming. It's going to be up to us."

Jorv showed up a few minutes later, impatient to start. He wore a vacuum suit with the helmet tucked under his arm. “I've been suited up for an hour,” he said. “When do we go?"

“Not for a couple of hours,” Bram said. “They're getting the walkers wound up and rounding up supplies and equipment. And some of our people need time to get ready."

That was Heln. She was putting together her material on ants, bees, beavers, wolves, rats, apes, elephants, antelopes-all the vanished animals of Earth that had lived in groups. If intelligence had evolved from any of them, their descendants would resemble them as little as man resembled the tree shrew. Heln wanted to be prepared to spot basic characteristics and extrapolate from them.

“Why delay?” Jorv said pugnaciously. “Pick up a few extra air bottles and get going."

“Don't you want time to get organized?” Bram countered. Jorv had nothing with him, not even a camera or a pad to take notes on.

“What for? Get a look at them, I say. Plow through the data afterward."

Ame came around and put a hand on Jorv's arm. “It's not just a case of observing them, Jorv,” she said. “We'll work from your opinions—but we have to try to communicate with them, too."

“Why don't you meet us at the vehicle air lock in, say, two hours,” Bram said.

Jorv walked out, shaking his head and muttering.

Bram helped Jao pack up his computer signboard and image library, while Ame went to give Heln a hand and to collect Shira, her paleobiologist colleague. Heln turned out to be a small, pert redhead, loaded down with a portable reader, cartridges, pad and easel, recorder, and other equipment.

When they arrived at the walker stables, Bram saw that only two walkers were equipped and ready for him, not the three he had arranged for.

“Where's the other vehicle?” he asked the ostler, a squat, muscular man who was strapping a spare air tank on one of his charges.

“He took it,” the ostler said. “Your friend. Said he was getting a head start, that you'd catch up with him."

“Jorv?"

“Short chubby fellow, sort of a restless way with him? I told him that I wasn't finished packing it up, but he said as long as it had enough air and power on the meter to get him there, it was good enough. He almost wouldn't wait long enough for me to put in a reserve air tank. I said to him, you don't want to go out there without one—never mind that you're only one person in a life-support system that's supposed to handle three."

“How long ago?"

“About two hours."

Bram turned to the others. “I don't know what he's up to, but we'd better run him down before he gets there."

“We'll have to triple up,” Jao said. He looked at the mound of gear they had brought with them, then his eye lit on the red-haired sociobiologist. “Why don't you and Ame and Shira ride together, and Heln and I can squeeze in with all this equipment."

The walkers loped side by side across the dim plain, stretching their legs of plastic and synthetic protein. Their yellow headlamps bored into the endless ribbon of rubblescape ahead of them. They had traveled far enough so that the tethered moon was at their backs, showing its shape like a child's top. To their right was the bloated face of a disk, casting a rusty light. To their left were the deeps of space with a hoarfrost of stars.

“Not a sign of him,” Bram said.

“Don't forget, he's running lighter,” Ame pointed out.

She was squeezed against him on the narrow bench. On her other side, Shira's bony hip dug into her. The lanky paleobiologist said, “He's had a two-hour head start. But Jorv's not a good driver. He'll try to hurry his walker too much, and that'll mean that its legs will just be churning around in midair a good deal of the time."

“Could we have passed him somehow?"

“We can see clear to the edge on either side. We'd have noticed his lights."

“If he remembered to turn them on,” Shira said, and fell silent.

“We've been running for three hours,” Bram said. “We'll be there soon. If we were going to catch up to him, we'd have done it by now."

“Don't worry, Bram-tsu.” Ame said. “Jorv is a very intelligent man. He won't do anything too rash. All he wants to do is study them."

“They may be studying him by now,” Bram said, and urged the walker on.

An hour later, the great pearly dome of the alien bubble grew out of the dimness ahead. There was no question of it appearing over the horizon—not on the diskworld. It simply became visible as a dot and grew larger.

Bram slowed the walker and approached at a trot. Jao, driving the other walker, fell in beside him.

The aliens were deploying around their bubble, queer sticklike creatures who hurried back and forth, carrying huge cone-shaped containers that they peeled open to reveal equipment and housing materials. Wheeled vehicles, whose barrel-shaped tires seemed to be clustered at one end, leaving a tubular chassis projecting with an upward cant, were being readied. All the activity was taking place under the glare of work lamps set up on tall stands around the perimeter of the camp.

“They like things bright,” Ame said, looking at the pool of light around the tremendous ball.

“Look, there's Jorv's walker,” Bram said.

The spindly vehicle, its bubble deflated, stood a short distance from the equipment-littered area of activity. There was no sign of Jorv himself.

“Collapsed bubble,” Bram said. “It should have reinflated itself by now. I hope Jorv's not—"

Shira tossed her head. “If I know Jorv, he was careless about getting out, that's all. Walked away and left it unsealed."

“Bram-tsu,” Ame said. “Do you notice something strange?"

It struck Bram after a moment. “Yes, why aren't there swarms of those creatures around the walker for a closer look at it? It's just sitting there. Don't they have any curiosity?"

“Maybe Jorv's getting all the attention."

“No, he isn't.” Jao's voice came through the suit radio. “There he is, wandering around in the middle of their camp, and they're ignoring him."

Bram spotted the human figure after a moment. Jorv was dawdling about in bemused fashion, pausing here and there to look at things that interested him. He might have been out for a Tenday stroll. The stick creatures hurried past him on their errands without stopping.

It wasn't quite true that they were ignoring Jorv, though. Jorv got too close to some piece of equipment that a group of them were setting up, and one of them detached itself from the work party long enough to make a number of short, aggressive rushes at the space-suited human. Jorv scrambled back out of the way. Bram couldn't blame him; even from a distance the rushes looked scary. Jorv kept his distance, and the alien went back to its work, paying no further attention to him.

As the walkers cantered closer, Bram was able to make out more details of the creatures. They were long, tubular beings with pipestem limbs that seemed to grow out in a cluster from just below an oversize head. They walked upright on all fours, like animated plant stands—keeping the trailing portion of their bodies from scraping the ground by curling it upward in balance.

“Our ancestors ran on all fours, too,” Shira said, mostly for Bram's benefit. “They learned to knuckle-walk, so that they could carry things at the same time. That's why evolution let us keep forelimbs we could manipulate with."

“It made for the development of intelligence,” Ame agreed. “But these creatures never adapted for a two-legged gait. I wonder if..."

Bram studied the distant figures. The beanstalk creatures seemed not at all handicapped by their quadruped stance. The forward pair of legs did double duty as arms, and when the creatures carried things—tottering in the low gravity and intermittently dropping a front limb for temporary balance—Bram was amazed to see the tubelike abdomen curve flexibly around to assist with the grip. There seemed to be a clasping member at its tip.

The creatures wore enormous boxlike helmets that were far too large even for the oversize heads that could be seen shadowily within. A human child could have curled up inside.

“They want lots of room in those helmets,” Bram said aloud. “I wonder why."

He reined the walker to a halt next to Jorv's abandoned vehicle. Jao and Heln pulled up behind him.

“We'd better walk from here,” he said.

The five of them climbed to the ground. The pipestem figures in their unwieldy many-faceted helmets made no move in their direction. They went on with their restless scurrying to and fro, never pausing in their chores.

“Do you see what they're doing?” Jao said, putting a hand on Bram's sleeve.

Bram looked over to where the floodlights lit the underside of the tremendous cloudy ball that had been first a fuel tank, then an environmental module, then a landing craft.

It was growing all sorts of attachments. An undergrowth of prefabricated polyhedrons. Huge glistening balloons that were blown up and sprayed with hardening foam to become permanent structures. A network of tube-ways and covered platforms that connected with the beginnings of some kind of large excavation.

“That lander will never go anywhere again,” Jao said.

Bram nodded. “They're here to stay. First spot they touched down on. I get the feeling it could have been anywhere on the rim. They didn't waste any time unpacking, either."

Heln came over, festooned with cameras and recorders. “This is all I'll need,” she said. “I'm leaving the rest of it in the walker. I was able to go through most of the material on the way."

“Any ideas?” Bram asked.

“I may have. First I want to see if Jorv and the others can pin down a working phylogeny for those creatures. I can tell you one thing, though.” She hesitated.

“Go on."

“They're not a contact species. But they observe a hierarchy of space.” She saw his puzzled look and added, “You see, it would affect their social organization—and the way they communicate."

“You can tell all that by looking at them from a distance?"

“On average, they maintain a uniform separation between themselves of about one point five limb lengths in close working situations.” She gave a troubled frown. “The limits of fang and claw, you see. In humans, it's about three feet. But the real clue came from Jorv."

“You mean when he got too close to that equipment and was warned off? I suppose it shows that these beings are touchy."

“No, not necessarily. They may inhabit a different universe of perception. Communication with them may not be a matter of language, or symbols, or images."

She cast a glance at the folded easel of the computer signboard that Jao was removing from the walker.

“I don't understand,” Bram said.

Heln hesitated again. “I don't believe they're aware of Jorv."

“But they saw him. They rushed him till he backed off."

“That's not what I mean. I mean they're not aware of him as an entity. They're aware of the alteration of hierarchical space that his presence caused."

Jao paused in his labors. “Just like physics,” he said. “The shape of space is defined by the presence of matter."

Heln pursed her lips. “I know it might not seem to make much sense..."

“No, no,” Bram said hastily. “In the physical sciences we reason from a single datum sometimes and reach the most astonishing conclusions. You've got a new science here. We'll take your word for it."

Ame was anxiously surveying the scene within the floodlit area. “Jorv just got himself chased again,” she said. “We'd better get over there before he gets himself into trouble."

“Yes,” Bram said. First he checked the air bubble of Jorv's walker. It had deflated because the thickened edges of the gasket were misaligned. Shira had been right about Jorv's carelessness. He must have shouldered his way out of the vehicle frontally, probably spreading the bubble's lips apart with his hands, then letting them snap back into place. Bram realigned the closure and saw some of the collapsed folds begin to stir and rise; they might need that air on the way back—Jorv hadn't bothered to set out with a full complement of reserve air bottles, and if he'd had to get back home on his own, he might have made a close thing of it.

Jao slung his computer over his shoulder, and Bram shouldered the folded easel. Ame, he saw, had a big pad under her arm; she and Shira relieved Heln of some of her excess equipment. Together, they danced lightly across the landscape toward the stick-people's camp.

As they approached the lit area, two of the spindly creatures trotted by at close hand, bearing a large, lightweight construction panel between them. Their gait was three-legged, and the long tubular abdomens, with gauntleted pincers on the ends, were curled around for extra support. They were backlighted by the brilliant lamps, and through the cloudy sheaths that covered their bodies, Bram got an impression of stiff, slender, many-jointed legs. The huge boxy helmets, concealing their secrets in the reflected glare, made them look like walking packing crates.

Jao stepped forward, holding up an outspread hand, but the creatures veered off to join a work crew at the perimeter of illumination.

“You'd think they'd have stopped,” he said, affronted.

“Different body language,” Shira suggested. “Holding up a hand doesn't mean the same thing to them."

It sounded reasonable to Bram, but he saw Heln's pursed lips and frown of concentration.

They moved into the light. Bram saw Jorv's space-suited figure ahead, stalking one of the stick-creatures. Jorv approached at a crouch, the lines of his body an exaggerated study in caution. The stick-creature was half turned away, flexing its reedy legs, its sheathed abdomen twitching slightly. It let Jorv get within eight or nine feet, then, abruptly, its legs bunched like springs and it soared over his head and lit down next to a pile of construction materials, where, without preamble, it joined its fellows in putting up one of the polyhedral structures.

Jorv straightened up, every line of his body showing disappointment, and began stalking another one of the creatures.

“We're not even going to get that close to one,” Jao grumbled.

Every time Bram and his party seemed about to intersect the path of one of the creatures, it veered off and ignored them.

“Just hold on,” Bram said, “and we'll be in the thick of them."

“I'm insulted,” Jao said. “Am I invisible, or what?"

Heln said, “They see you ... but they don't see you."

“Maybe they're some kind of hive creatures,” Shira put in. “No real intelligence. The intelligence is in that bubble they landed in."

“They've got intelligence,” Bram said. “If intelligence means handling tools and machinery."

Then, without warning, they were upon one of the creatures. It reared up in their path, the light shining full on it, and for the first time Bram got a good look at what was inside those cagelike helmets.

Its face was the stuff of nightmares—two bulging domes of jelly on either side of a masklike bulb that was split by a vertical cleft. Each of those jellied eyes—if that's what they were—was the size of a man's head.

The cleft parted in a hideous vertical smile that hinted at something spiny and complicated within. There was a flicker of movement in front of the ghastly face—and in a moment of startled disbelief, Bram saw why the creatures needed so much room in their helmets.

There was a separate pair of limbs within the helmet!

They grew out of the creature's face, or the sides of what passed for a neck. They were smaller manipulating limbs—shorter than a man's arm—and these peculiar beings kept them folded up on the floor of the helmet, like a person resting his elbows on a table.

The creature swiveled its complicated head as if looking for a way of escape, and the facial limbs lifted and swung with it.

A flash of crazy thought went through Bram's head: It must cramp their style to be deprived of the use of their grasping members whenever they wear space suits! But the creatures’ anatomy gave them no alternative. Limbs projecting through sleeves in a smaller helmet would have immobilized their heads.

Or maybe they simply needed to have their forelimbs available for grooming or self-care. Maybe they would have felt uncomfortable having the limbs enclosed apart from their faces. Bram could sympathize with that—hadn't he suffered the agony of being unable to scratch an itchy nose while wearing a space suit?

Everything had happened in an instant. Through his radio Bram heard a couple of people gasp—he felt like gasping himself—and then the jelly-eyed horror spun around and galloped away.

“It saw us,” Jao said. “I swear it saw us that time."

“No,” Heln said. “It saw the effect we were having on its visual field."

“What's the difference?"

“Have you ever heard of an animal called a frog?"

“Huh?"

“Wa, in Chin-pin-yin. The children's story about the mandarin who turned into one."

“Oh, yar."

“It saw motion, not objects. It ate an animal called a fly, but it didn't see the fly until it moved. If you tried to feed a captive frog on dead flies, it would starve to death."

“Are you saying that these tomato-eyed beasts are frogs?"

“No,” Heln said patiently. “I'm saying that they have a queer sort of brain wiring that enables them to cooperate as a species but that makes other life forms irrelevant to them—as irrelevant as a fly is to a frog ... until the fly moves. We're no part of their experience—or their instincts—so we don't exist for them."

Bram looked around at the teeming campsite. “Aren't you overstating the case? These aren't primitive animals. They've got space travel. They must process information somehow in those heads of theirs. Can you have intelligence without curiosity?"

Something was bothering him. It was Jao's description of the creatures as “tomato-eyed.” It was true. The eyes were reminiscent of gigantic green tomatoes. A memory nagged at Bram somewhere below the level of consciousness.

“Maybe.” Heln stood her ground. “And maybe you can have intelligence without empathy. Maybe we're going to find that these new neighbors of ours lack basic empathy-that it's literally impossible for them to relate to any life form but their own."

“That would certainly make it hard to communicate with them,” Ame said with a strained smile.

“To say the least,” Bram said.

“I hope not,” Heln said, shifting some of her technical accoutrements on their carrying straps. “There has to be a way for us to plug ourselves into their sensory wiring. We'll just have to find it. Let's hear what Jorv has to say. Maybe he has some ideas about their phylum by now."

Jorv saw them coming and ambled over to greet them. He seemed preoccupied. “They may be descended from terrestrial insects,” he said without preamble. “Did you notice those wraparound eyes? They probably carry the efficiency of the compound type of eye as far as it can go—their visual acuity may surpass our own. And the muscle attachment—I wish I could make out more through those space suits. They don't move as if the muscles were operating proper skeletons!”

Bram tried a mild reprimand. “Jorv, you shouldn't have come out here on your own. We may be running up against a very queer situation."

“Queer? I'll say it's queer. They won't stand still long enough for me to get a good look at them. Did anybody bring cameras? Ah, Heln—you'd better start taking some pictures."

“Did you try to talk to them?” Bram asked.

“Talk? They won't talk. Ame, I think you may have hit on something when you deduced a hookup between sensory input and a visual grid from their radio signals."

Ame looked excited. “The compound eye means there's no overall image—just a very large number of separately perceived patches. The visual information jumps from facet to facet, whether the object is moving or the creature's head is moving, and the sum of the signals is processed somewhere in the brain—"

She broke off. Everybody looked at Heln. “Your frogs,” Jao said.

“What have frogs got to do with it?” Jorv said irritably. “These are insects!"

“Very big ones if that's true,” Shira murmured. “Insects shouldn't be able to grow to that size, with exoskeletons as a limiting factor. And they were lungless, weren't they? They transported oxygen through tracheae. That would limit their size, too."

“We won't know till we examine one!” Jorv's eyes were gleaming. “Do you think you could help me get one back to our camp?"

“Sit on him if you have to,” Bram told the three women. “Jao, let's get your computer signboard set up."

They worked at it for fifteen hours, taking turns going back to the parked walkers to replenish their air supplies and to fetch various items that Heln or Jao had brought along in hopes that they would help.

Nobody ate a lot during that time—just a few hasty handfuls of travelfood that had been included with their rations—and nobody slept at all, despite the fact that all of them had been awake for more than twenty-four hours.

They got nowhere.

Every once in a while one of the stick-beings would dart over and pause for a look at the computer display or at an earnestly semaphoring human being. At least they seemed to be looking. But they always trotted on past without showing any reaction.

Once an exasperated Jao had stepped squarely into the path of an ambulating beastie and attempted to herd it with blocking movements of his wide torso toward the little communications arena. An observer could not have said that the intercepted individual exactly tried to evade Jao. Simply, it was somehow past him without appearing to have noticed his presence.

It was a pity, because Jao had knocked himself out to prepare his visual displays. There was a beautiful sequence in simplified diagrams and actual images that showed the human itinerary from the Whirlpool Galaxy to the Milky Way to the vicinity of the enclosed star that was presumed to be Delta Pavonis. Another sequence ingeniously arranged as a query showed the presumed progress of the tomato-eyed strangers from a presumed Sol.

Jao never got anywhere near to unveiling his masterpieces—a sophisticated scenario that showed the ancient origin of humankind on a planet of Sol, showed bright schematic images of DNA, and showed the diskworld itself with stylized radio waves spreading from it toward the Virgo cluster of galaxies. It went on to show the Whirlpool in the Canis Venatici cloud, halfway to Virgo, being bathed in the radio waves, the reemergence of the colorful DNA schema, then the recreation of human beings and their return to the planet that had given birth to their genes.

“They don't take visual information!” Jao said in disgust. “And them with eyes as big as my head!"

“It's not visual information, it's abstractions,” Bram said. “Let's show them something closer to home."

They displayed images relating human figures to Yggdrasil, with much pointing at the green blob that could be seen over the horizon. They showed the fuzzy images of the stick-ship and finally life-size holos of the jelly-eyed creatures themselves, played back from Heln's camera.

But when Jao projected one of the fearsome holos in the path of one of the trotting creatures, it passed through it without pausing. “It didn't see the image as real,” Ame said. “Not polarized for their eyes."

“But sometimes they do seem to pause for a second and show body reactions, particularly with the moving images,” Shira said, sounding frustrated. “And certainly when we get too close to their precious equipment."

“The same way your feet find stepping-stones when you cross a stream,” Heln said. “Doesn't mean you're really aware of the stones."

Heln, tree-born, had never seen a stream and certainly never had crossed one on stepping-stones, but Bram appreciated the aptness of the simile.

“Going to try just one more thing,” Jao grunted.

He generated an animated image of a Cuddly, and the next time a stick-creature intersected their little communications arena, he sent it scampering toward the being.

The alien being stopped dead in its tracks and stood stock still for all of two or three seconds. For a moment Bram thought it was going to rear up and change direction, as it did when a human got in its way. The nightmare face seemed to expand as the central cleft widened, and Bram thought he saw a flicker of movement within the cavity.

Then, apparently, the creature dismissed the holographic Cuddly and darted off on its interrupted errand.

“We almost had it that time!” Jao exclaimed. “Did you see that?"

“But why?” Shira asked. “It couldn't have seen the holo as real."

“Something in its neural circuitry reacted,” Heln said. “Something about the image almost tripped a switch."

“But what?” Bram wondered. “The Cuddly's size? Its movement? Its resemblance to something it is primed to react to?"

“Maybe all of that,” Heln said. “But it shows that the switch is there, ready to be tripped. And maybe after we get back and have time to study our film and data, we'll be able to figure out how to get them to notice us."

They kept at it until their margin of reserve air was almost gone. And then they had trouble prying Jorv away. “They're insects, all right,” he babbled happily. “Or at least in the insect line of descent. It's all there in the jointing of the legs—the two short basal joints, femur and tibia meeting at the knees, then the three short joints and former claws of the tarsus. I'd give my eyeteeth to see them out of their space suits."

Bram had Jao drive Jorv back; he didn't trust the pudgy zoologist not to return to the alien campsite. Before they entered their separate vehicles, Bram exchanged a few words with Jao.

“Did you notice there were no Cuddlies hanging around? That's odd ... there must be a few burrows in the area, and they're such curious little beasts."

“Huh? They're probably just being cautious till they figure these insect-people out."

“Heln says that maybe we'll be able to figure out how to trip that switch in their brains after we learn why they reacted to a Cuddly image."

“What are you getting at?"

“Maybe we won't want to."

It was hard for Bram to keep the curious from sneaking out to the insect-people's base camp. “Not until we know more,” he insisted. “The specialists are working on it. We don't want to take the chance of stirring them up till we have some chance of communicating with them."

In the meantime, Yggdrasil was drifting inexorably farther away. Smeth called several times a day to display fits of ill temper.

“We were supposed to leave this system within two Tendays from now. Jun Davd's got our course worked out for that window, and my black gang's warming up the fusion drive. We're halfway through our checklist. We've already got a starter ball of deuterium slush in the throat of the scoop, and it's evaporating with every second that goes by.” His words became a wail. “And where's Ame? She was supposed to be back here days ago! The twins are acting up, and I don't have time to handle them by myself."

“I'm sorry,” Bram said. “I couldn't get Ame to leave now if I tried."

“Well, it's not every day you run into a new intelligent life form,” Smeth said grudgingly.

“I can't get anyone else to leave, either,” Bram told him. “We may have to change our plans. We can't leave this system without knowing more about what's waiting for us at Sol. We may not own it anymore—not if these are the new inheritors."

“If we don't pack up and go soon, Yggdrasil will have to make another circuit. It would use up our whole starter ball. We could be delayed another year."

Bram broke it to him gently. “I think that's what it may take. We're going to have to put it to a vote."

“Don't say that! Jun Davd spends all his time looking at the pictures and data you sent up. I've been trying to get some revised escape orbits out of him, but his computer's all tied up with an analysis of the radio traffic that—that colony sent."

“Sent?"

“Yes, it's stopped. They don't seem to have anything more to say to one another. Jun Davd says the colony's on its own."

“Is he getting anywhere with his analysis?"

“No."

Jun Davd was interested in Heln's theories. “A life form that lacks basic empathy on a neurological level. It's a chilling thought for us humans. Very frustrating. Our only other relationship with intelligent beings was with the Nar—probably the most empathetic life form in the universe."

“I've forbidden our people here to go visit. But I know they sneak over there anyway, make a party of it. Walkers are checked out and are gone for twelve or fifteen hours. I can only hope they're watching from a distance. The insect-folk themselves are sending out pickets. Those wheeled vehicles of theirs are spreading outward in reconnaissance patterns. They're probably looking for expansion sites. I hope there are no encounters."

“And if there are?"

“According to Heln, they'll see the human beings as a detail of their environment. An unimportant detail. Irrelevant."

It was an audio-only circuit, but Bram could almost see Jun Davd shake his head in bemusement. “What if some impatient idiot grabbed hold of one of these creatures?"

“Then he'd be a relevant fact of the environment. That's the kind of encounter I don't want."

“I hope your terrestrial life specialists come up with some answers soon. People here in the tree are agog at your pictures. We can't keep them penned up much longer. You're liable to have tourists."

Bram groaned. “That's all we need."

“Heln believes that there may be a switch in the neurological makeup of these insect folk—a switch that would make us a part of their perceptions—and that this switch can be tripped if we find the key?"

“Correct."

“And that once tripped, it will stay tripped for them as a species?"

“Yes."

“Extraordinary!"

“Heln's delved into volumes of biological lore from the buried libraries and says there are all sorts of examples of these neurological switches—they're called ‘releaser’ mechanisms—in terrestroid life. If the animal's nervous system is complex enough and there's a degree of social organization, the perception of the triggered individual becomes the perception of the species."

“What if the perception is something we won't like?"

“All we want to do is get them to notice us."

“Be careful."

“I'm on my way to see Jorv now, to see if he's made any progress in tracing their species."

“The claspers at the tip of the abdomen were characteristic of many insects,” Jorv said happily. “Like paired forceps. Insects developed an opposing grip before our own ancestors did. Only they had it in a different place."

He looked up at Bram, pleased with his little joke. Jorv had gotten an artist to prepare diagrams from Heln's pictures, and these were spread out on easels around him.

“Odd place for a hand,” Bram said.

“Not when you consider the purpose."

“Which was?"

“To assist in copulation.” Jorv licked his lips. “A useful accessory, particularly for species that mated in flight."

“These creatures don't have wings."

“No, but I'll wager an autopsy would show vestigial wing muscles, just as human beings have vestigial tails. They lost the wings somewhere along the way, as ants did."

Jorv pointed at a picture tacked on the wall, showing a spiny, many-legged creature with fearsome jaws—a blowup from one of the old texts he and Heln had been delving into.

“Are they ants?"

“No. I haven't been able to find a form they correspond to—not yet. There's something puzzling about them."

Bram looked again at the diagram of the abdominal claspers. They were heavily gauntleted, but their form was plain enough, as a gloved hand is.

Jorv continued happily babbling. “The female claspers for gripping the male would have been in a different abdominal segment, but that doesn't mean anything. The structures would have been there embryonically, and if evolution decided they would make a useful hand, a similar appendage could have developed from the ovipositor."

“Ovipositor?"

“For laying eggs. It was generally equipped to puncture holes in mud, vegetation, or some other hatching medium. Living flesh, I'm afraid, in the case of some of the nastier species."

“Insects seem to have been a remarkably single-minded life form."

“In the sense of a will to survive? So were our own ancestors, no doubt. But those creatures building their city out there have developed intelligence. They've learned how to survive and propagate through technology. Don't worry. Once we get a key to their developmental patterns, we'll find a way to communicate with them."

“I hope so."

Jorv frowned. “I still haven't decided whether their ancestors were plant eaters or meat eaters. The mouth parts are hidden inside that odd facial structure. There were over a hundred million species of insects, and so far I haven't been able to find anything like it."

Ame came over with a new sheaf of blowups. “Hunters or browsers?” she mused. “It would be nice to know before we meet them again."

* * *

As it happened, it was the insect-folk who made the first move. Bram was having a meal with Ame when he got a call from one of the watchers he had posted on the plain.

“Bram-captain, one of those tube machines is rolling in your direction. It zigzags a lot, but there's no doubt about where it's headed. It should reach the digs in about an hour."

“Thanks. Stay where you are. Keep an eye out for any more of them."

He stood up. Ame said, “I'll get the others."

“Tell them to keep their distance till we see what they're up to. Let's see what they have in mind, for a change."

He deputized a dozen people for crowd control. “Tell everybody to stay out of their way. Don't interfere with them. If any approach is made, it will be done by one of the specialists."

An hour later, the excavated streets were full of waiting people. Word had gotten around fast. They sat on ledges, hung over the low rooftops that had thrust themselves out of the rubble, and loitered in the stone arches. Bram had a vantage point from the top of one of the buildings facing the moon plaza. If the insect surveying party kept to the avenues of rubble leading into town, this would be the major route.

“There it comes,” Jao said beside him.

A tiny shape appeared in the distance and soon resolved itself into one of the tube vehicles, bumping along on its fat tires at about twenty-five miles an hour. The four barrel-shaped rollers were all grouped close together under a cab that seemed to carry most of the weight; the long, slender cylindrical body tilted upward at a thirty-degree angle behind it, doing a lot of vibrating. Bram supposed it made as much sense as any other design for rough country; if the cab had to crawl over an obstacle, the projecting section had plenty of leeway to tilt downward without dragging.

The bizarre vehicle rolled by the crystalline shafts of the moonropes without slowing down and came to a quivering stop at the edge of the wide plaza. Bram could see human figures peeking at it from around corners.

He waited for a door to open, but none did. After a few minutes a boxy helmet emerged from the end of the tube, about twelve feet above the ground. The rest of the insect-person extruded itself, hung rigidly horizontal from the lip of the tube by the claspers at the tip of its elongated abdomen, and let itself drop lightly on all fours to the ground. Seven more of the creatures followed.

They stood around, conferring with twitching movements of their long sterns. Bram saw little, discreet flashes of lights from their helmets and assumed it was the polarized light version of radio communication. After getting everything settled to their apparent satisfaction, they slung equipment over their humped shoulders—or hips, if that's what they were—and began skittering down the long boulevard with lots of nervous, darting side trips, staying in a loose group.

People began to drift down from rooftops and emerge from side streets to trail after the insect-people at a respectful distance.

“We'd better get down there,” Bram said.

He vaulted over the rooftop and floated to the ground, with Jao close behind him. He strode in thirty-foot bounds across the plaza and caught up with the little parade going down the avenue.

Trouble started almost immediately. A skylarking fool who had been leaping up and down in great swoops shot fifty feet into the air and came down squarely in front of one of the insect-people. Apparently he got a good look at the jelly-eyed face within the helmet, because he backed away with a jerk and stumbled.

The insect-being showed no signs of-stopping, and the skylarker showed no signs of getting out of its way. Jao reached the spot in one long soaring arc and snatched the offending person out of the way with a hand hooked into the webbing of the life-support backpack.

He bore his kicking prize to Bram. He did not set the fellow down on ground, but held him out to Bram at arm's length.

The face within the helmet was that of a junior archivist named—Bram rummaged in his memory—Alb something-or-other. Alb was less than thirty years old, having been born in the heart of the Milky Way, and hadn't lived long enough to develop good sense.

“Put him down,” Bram said.

Instead of letting go, Jao rammed the errant archivist into the ground with some emphasis. Alb stood there with a silly grin on his face.

“Alb, I thought I told everybody—” Bram began.

“He can't hear you,” Jao said. “He isn't tuned in to your frequency.” He made twisting motions to get the idea across to Alb, but the young man just stood there stupidly, no doubt listening to the gibes of his own circle of friends.

“Oh, chaos take it!” Jao exclaimed. He dialed through his own frequencies till he hit Alb's. He must have turned the power full up, to judge by the way Alb flinched. Somewhere out there a number of other people must have acquired an earache too. Jao proceeded to give the unfortunate fellow a dressing down. Bram tuned in for the tail end of it: “...brains of a three-legged baggage walker!"

Alb gave Bram a sheepish apology and promised to behave. Bram heard group laughter on the frequency, and Alb turned pink.

They caught up with the insect patrol some distance down the avenue of rubble. Jao's lecture seemed to have had good effect; the trailing crowd of people was hanging back farther. One of those who wasn't lagging behind was Heln Dunl-mak. She skipped ahead of the alien party, just beyond what she had described to Bram as the insect-people's “avoidance zone."

Heln's slight figure was top-heavy with improvised equipment—a bulky pack that Jao had put together for her. It was flashing modulated polarized light, some of it drawn from frequently appearing patterns in the stick-ship's early radio transmissions, some of it repeating and stringing together “phrases” that the darting aliens were blinking at each other.

“Best program I could cobble together at short notice,” Jao said apologetically as he waved at Heln's dancing form. “Heln doesn't really know what she's saying to them, but she can punch in a few crude menus based on their physical behavior, and the computer can try to correlate it with what they're flashing to each other at the time. Then it runs through all the combinations. With luck, we'll get a ‘turn right,’ or ‘follow me,’ or ‘look at this.’ It's up to Heln to recognize a response."

But there was no sign of recognition from the insect-folk that Bram could see. By stretching his imagination to the limit, he might at best have concluded that they showed a sort of irritation or brief annoyance—analogous to what a human might display if a light were flashing in his eyes or if he were trying to talk with a radio on in the background. But such distractions, really, were below the level of awareness.

“The computer's learning all the time,” Jao said defensively. “Sooner or later it might hit on something."

“What you've done is amazing,” Bram assured him.

Jao brightened. “Want to know what the hardest part was? It wasn't the program. It was inventing the gizmo to recognize the polarization through different planes of orientation, then to transmit the same way. That's what takes up so much room in the backpack. I had to scavenge the faceplates of a whole bunch of helmets to build it."

Heln, arms spread low, purposely penetrated the avoidance zone and dropped to one knee, then danced back as the creatures showed restlessness. Her equipment blazed a signal that looked sustained to human eyes but that to the aliens, of course, would have flickered. Bram saw the shadowy facial limbs lift as if to ward off something, but the creatures never stopped their prowling movements.

“They still don't see it as speech,” Jao said. “Something missing."

“Very frustrating,” Bram said.

One of the insect-people was using an odd camera—a sizable box with one curved face studded with thousands of pinhole lenses. It took its pictures by sweeping areas of the ruins in short arcs.

“Multiple fixed-focus lenses,” Jao said. “Motion shifts the pattern. They must have some way of reading the result. Like Heln said, it's the way they see."

“They're not much interested in the people,” Bram said. “Or individual objects. They seem to want fields of view."

“Looking for another place to light,” Jao said. “The digs here are ready-made of them—honeycombed with chambers connected by a tunnel system."

“No,” Bram said. “We can't allow that. We'll be coming back here someday. We've got to talk them out of it."

“First we've got to find a way to talk to them."

The insect-people spent the next few hours exploring, completely ignoring the holiday crowd that tagged along. After a while, Bram became aware that their seemingly random forays added up to an extremely efficient search grid.

Besides the camera, whose purpose was obvious, they used a number of other instruments. One was a long stinger that came out of a cylinder on legs and penetrated the ground to a depth of—Bram estimated by counting the telescoping sections—thirty feet, at least. The tripod gave a little jump when it hit bottom. “Their version of a thumper,” Jao said. “They're searching for cavities.” Other instruments, with a little thought, were soon recognized as a surveyor's transit and a range finder, adapted to the peculiar insect vision.

The creatures seemed to get restive after a while, and after they had darted at one another in a series of little mock attacks, they all filed back to their vehicle, launched themselves up into the end of the angled tubular chassis, and disappeared inside. Bram waited, but the barrel-wheeled vehicle showed no signs of starting up.

Heln sauntered over. “Lunch break for them,” she observed. “Or some kind of break. Whatever it is, they've got to take off those helmets to do it."

After twenty minutes passed, the creatures popped out of the end of the tube again and resumed their mysterious activities. Several of them could be observed preening their nightmare faces. Jorv appeared with an assistant, who took more pictures.

At the end of another couple of hours, the creatures found the ramp to the parking garage under the sports arena. This seemed to excite them. There was another head-to-head conference, with eight long tail sections sticking out and wobbling, the gauntleted claspers working convulsively.

They knew about air locks. Afraid that they might damage the locks leading to the stadium interior, Bram had been about to order that the creatures be let through while someone held the door, but one of them figured out the human machinery at a jelly-eyed glance, and they swarmed inside. They even closed it behind them.

They seemed to be awfully good with machinery.

“They can notice inanimate objects,” Bram puzzled, “but not a crowd of people."

“You don't understand,” Heln said. “We are inanimate objects."

“Yar,” Jao said, as if he were an expert. “We haven't impinged on them."

A thought struck Bram. “They must have seen the shuttles parked in the field on their way through. If not man, then man's works! Why didn't they take an interest in those?"

“Held no meaning for them,” Heln supplied. “Wasn't important. Not like the air lock here. They wanted to get inside."

Bram spoke to his traffic control-deputies. “Keep the mob outside. I won't evict anyone who's already in there, but I think we'd better keep the numbers down."

Without their space suits, the creatures from Sol were an unnerving sight—spiny legs, globular green eyes, and hard shiny integument bristling with stiff hairs. The four-fingered claspers at their projecting rears were pincers of horn, and the forward manipulating limbs, now revealed, were all tweezers and hooks.

They prowled the floor and balconies of the chamber, taking no more notice of the gawking humans than humans would have taken of moss on a rock. With the boxy helmets off, the clicking noises they made to each other could be heard like a high-speed rattle of broken sticks.

Their insect ancestry was fully apparent. “You see,” Jorv said ecstatically, “how evolution modified the exoskeleton in a way that permitted them to grow to size. It became a partially embedded, hinged, mostly external skeleton that operates as a system of levers. The extensor and flexor muscles operate separately, bridging the hinges on opposite sides."

The skeletal apparitions gave everybody cause to remember their childhood ghost stories in Chin-pin-yin; the word for a foreigner was, literally, a “bones-outside,” and now Bram heard people around him starting to call the Earthlings that.

Jorv could hardly contain himself. “You see the pulsating of the abdomen? I think they breathe through their anus. I wonder what evolution gave them in place of lungs."

“What are they?” Ame asked.

“I don't know,” Jorv said. “They may have been aquatic. In that case—"

He was interrupted by a chattering Cuddly that skidded to a stop in front of the group and climbed up the nearest person to reach the shelter of human arms. The person happened to be Ame, who petted the fluffy little beast and cooed, “There, there, nothing's going to hurt you.” The Cuddly had ventured too close to a prowling insect-thing and had had second thoughts about approaching it.

The insect-beings, in fact, had quite an audience of Cuddlies by this time. When the strange creatures had arrived and shucked their space suits, the couple of dozen Cuddlies that normally mooched around the chamber looking for handouts had immediately disappeared. After a while, when nothing much happened and the human beings seemed unconcerned, a few cautious little furry heads had popped up.

Now the Cuddlies were getting bolder. One fat little creature sat up on its haunches and scolded an insect-being that had paused, for a moment to survey the arena floor.

“Isn't that cute?” Ame said. “It wants the bones-outside to pay some attention to it."

“If we can't get their attention with computer displays and polarized light, there's not much hope for a Cuddly,” Shira said.

The little beast hopped closer and chittered more loudly.

“It's getting awfully close to the avoidance zone.” Heln frowned. “I wonder..."

“I think the thing's showing some reaction,” Jao said.

The face-legs, liberated from their box, swung idly to and fro. There was something about the stick-creature's stance. It seemed to lower itself a few inches and become utterly still.

Encouraged, the Cuddly made another little hop forward.

There was a blur of motion so fast that Bram saw it only as an afterimage. The masklike face of the alien split vertically, and a long scooplike lip tipped with teeth flicked out and captured the little furry beast.

The hinged lip, longer than a man's arm, snapped back, bearing the ensnared Cuddly to a barbed mouth. There was a single high-pitched squeal, and then with two crunches, the Cuddly was gone. The lobes of the toothed structure folded over to become a mask again.

The hum of human conversation in the chamber stopped abruptly. People stood frozen. Every Cuddly in sight streaked for a hiding place and disappeared. The insect-being stood preening itself with its hooked facial limbs. Its fellows paused in their rambles and turned their jelly-domed heads in its direction.

In the stunned silence, Jorv stood with dropped jaw, breathing hard. Suddenly he exclaimed, “Odonata!” and before Bram could stop him, he stepped up to the immobilized creature for a close look at its face.

There was another blurred movement as the creature seized Jorv with its facial limbs and bit his head off.

A woman screamed. People came out of their trances. The creature calmly continued crunching its way through Jorv's neck and shoulder. Jao grabbed one of the picks that the archaeologists had left lying around. Bram found a steel pry bar. Several others joined them, and they ran to recover what was left of Jorv's body from the leggy horror that was chomping its way through it.

It wouldn't let go. A couple of men had Jorv's body by the feet and were trying to pull it away. Bram grabbed the creature by one of its facial palps and tried to lever its jaws open with the pry bar. A hooked leg came up and raked him across the ribs. There was a sound of ripped cloth and a searing pain, but he held on. Jao swung his pick handle and smashed one of the bulging green eyes.

Even then it wouldn't let go. It rotated in injured circles, still munching, lashing out at the struggling men with its barbed legs. The long abdomen whipped around and a man screamed as its horned pincers tore at his flesh.

Bram went berserk. He beat at the armored hide with his steel bar while Jao, grunting, labored with his pickax at the ruined jelly of the head. The thing refused to die. The limbs slashed blindly at the air. But it dropped its grisly meal, and the long toothed lip struck out again and again, looking for prey. Finally someone got a sharpened pole—one the diggers used for soundings—and ran the creature through, repeatedly, till it stopped moving.

Bram stood wearily, drenched in blood and gore, holding the slippery pry bar. He couldn't tell how much of the blood was his own and how much had spilled from Jorv.

Shouts and screams echoed through the huge arena. The other insect-creatures, as if by a common signal, had gone on the attack. On a high balcony, the tragedy of Jorv was repeated as a stick-being pursued a fleeing woman and caught her with its facial snare. People came running, too late, to her aid. They beat and stabbed at the creature with whatever came to hand. One of the rescuers was flung away, disemboweled by a stroke of a hind claw. The tattered body tumbled slowly through the air toward the distant floor below.

Elsewhere, one of the spindly horrors ran at a group of people and emerged with a screaming victim in its mouth. It ran off with its prize, munching as it went, dropping a trail of arms and legs behind it.

Two more of the insect-beings bore down on the group of shaken people gathered around Jorv's headless body. They were a terrifying sight, but no one ran. An extensible lip shot out and clasped someone's leg in its prehensile hooks, but two quick-witted people threw themselves on the victim and prevented him from being dragged back. Men and women with poles, shovels, axes—anything that could be used as a weapon—converged on the monster from both sides. It loosed its grip, leaving a mangled leg that would have to be regenerated if the victim lived, and swung its three-lobed head at its tormentors. The lip raked across one victim, tearing flesh, and another man went down under the onslaught of the barbed head-legs. But other people harried it from behind, and when it swiveled its killing apparatus around to deal with them, a brave woman with a pole leaped high into the air and jabbed at a globular eye from above.

Meanwhile Bram saw the other creature rushing straight at him. The facial limbs were already extended for grasping. He knew he would be no match for the lightning thrust of the feeding apparatus—it surpassed his reach, even with the iron bar in his hand.

He dropped the bar and wrenched one of the heavy display tables from the ground. He put his whole back into it, swiveling from the hips. It was a massive piece of rough carpentry, twelve feet long, laden with rock and metal fragments that the archaeologists had not bothered to pack up. In the infinitesimal gravity, he could have lifted a weight ten times as heavy, but speed was the problem, and he needed all his muscular strength to overcome the inertia.

The table became his shield as the creature's lip struck. There was a sound of splintering wood, and Bram felt himself being driven back by the thrust. A rain of jagged stone and metal pelted his adversary. Bram shoved back, hard, and the weight of the table helped him; his feet were braced against the ground, while his opponent, losing contact, clung to the table as Bram ran it at full speed into the wall.

Three or four people ran to help him keep the creature pinned against the wall while somebody finished it off with an ax.

They stood around panting. “We're monkeys, monkeys,” Ame sobbed beside him, and he became aware that she was one of the people who had helped him keep the creature pinned. “I thought we were human, but we knew in our bones how to gang up on them."

“All the rocks and junk confused it for a minute,” Jao said. “Just long enough."

That gave Bram an idea. “Throw things at them!” he shouted.

The carnage on the floor was terrible. The insects had better reach with their legs and facial snares than the humans did with their shovels and axes, and they were very quick.

Jao was the first to react. He scooped up an armful of archaeological detritus from one of the big tables and sent a hail of missiles at another of the spindly creatures that was heading in their direction. It veered off. A sharp fragment caught it in one eye. Its lip shot out reflexively to find an enemy.

People were quick to get the idea. There were plenty of sharp objects to throw: shards from the long tables, cast-off equipment, and rubble from the floor itself. A barrage of missiles peppered the creatures from ground level and pelted them from the balconies. They came from all directions, thunking into the stiff hides, finding pulpy spots. There was no way for the creatures to avoid them, as marvelous as their eyesight was and as quick as their reflexes were. Every time they made a dash at a group of people, they were met by a volley of hurled objects.

Not that they were always turned aside. Sometimes they barged into a group, knocking people over and lacerating them, and carried someone off. They seemed to have no concept that they were outnumbered.

And then some brainy person reinvented the spear.

It was only a kitchen knife lashed hastily to a pole, but its-owner—maybe losing his nerve about running it into an enemy personally—flung it at an insect-thing as it passed him. The blade hit a soft spot, and the creature ran by with the pole sticking out of it. Another person threw another improvised pike, then everybody who had a sharp stick seemed to join in. The wounded creature began to run in circles, snapping at the skewers in its hide, then grew weaker and less purposeful, sinking to its four skeleton knees. When the surrounding people saw that it was safe to approach it, they hacked it to pieces.

Something new had entered human affairs—a thing that could kill at a distance.

It was over in another fifteen minutes—not without more human casualties. The last insect survivor, seeing that it was alone, fled.

“Don't let it get to its space suit!” Heln cried.

A bunch of people took off in pursuit, but it evaded them. Later, Bram reconstructed what had happened. The insect-thing had killed two people it found in the tunnel on the inner side of the air lock, retrieved its space suit, and charged into the crowd outside. With its coffer of a helmet on—its facial limbs caged up, and, perhaps, its senses muffled—it was no longer aggressive. Nobody outside knew what had been going on. The crowd parted to make way for it, and the deputies were pleased to see that nobody interfered with it. It hightailed it back to its barrel-wheeled vehicle and drove out of town.

The killing spree had left seven dead aliens and more than thirty dead and dismembered human beings. It was going to be hard to tell the enact number until the body parts that were strewn over the chamber were matched up. Bram moved among the weeping people, viewing the butchery. One of the dead was Alb, the junior archivist whom Bram had reprimanded. Somehow he had slipped past the deputies and gotten inside; poor Alb, he had thought it all a lark.

“I suppose it was the space suits,” Heln said, white as flour. “We didn't look appetizing to them inside ours, and their own feeding impulses were stifled with a sheet of plastic cutting off their sensory world.” She shuddered. “They like their food live and moving. I wonder what kind of livestock they carry with them in that tube vehicle of theirs."

Nobody had thought about that part of it. Ame looked ill. Bram remembered the creatures’ behavior just before they had taken time out to return to their vehicle for a rest break.

“Maybe animals about the size and shape of a Cuddly,” Bram said. “Possibly even mammals."

“Yah, the Cuddly popping up in front of that thing was what tripped the switch,” Jao said.

Heln gave the others a bleak look. “Yes, that and poor Jorv, sticking his face inside their unobstructed striking range. Their brains are rewired now. They've been programmed to see human beings. As food."

They spent the next day burying the dead—what could be found of them. Bram found some words in King James that seemed to express what everybody was feeling and read them aloud over his suit radio while the surviving human population stood around the grave site, heads bowed inside their helmets. The terrestrial biology group under Jorv's assistant took charge of the insect carcasses and began to do autopsies.

When Bram called Yggdrasil, Jun Davd urged him to close down the digs and return at once. “It's an unlucky place now, I fear. If Heln is correct, the danger's just beginning."

“I'm sending the first shuttle loads out today. We should all be evacuated by the day after tomorrow. In the meantime, I've posted a guard. The main thing is not to let them get inside the pressurized buildings with us."

“You ought to know that radio traffic between the colony and the father ship has resumed."

“They've renewed their connection?"

“For the time being. They had something to say to each other. You can imagine what it is."

“I take your meaning, Jun Davd. I'll try to speed up the evacuation."

“It's hard to abandon what we've found of our heritage, I know. But we were going to leave soon, anyway."

Bitterness clogged Bram's voice. “Yes, but we always meant to come back one day. Now..."

“Yes,” Jun Davd said somberly. “They'll have spread to the other disks by then. But Bram, we've done wonders in the year we've been here—thanks in large part to the spadework the rat archaeologists did for us. We've got the great libraries of mankind and a whole biological repository of extinct life forms..."

“I know, Jun Davd. We never thought we'd regain so much of our heritage. Still...” He felt suddenly weary. For the first time, the centuries of wandering seemed to have caught up with him—more than six of them by now, while the clock of the universe had ticked off its tens of millions of years.

“What did Jorv mean, ‘Odonata'?” Bram said.

Jorv's assistant, Harld, faced him, a scalpel in his hand, still looking pale and shaken. He had a thick white bandage on his head, covering the scalp wound he'd received trying to save a woman from the jaws of an insect-creature, and there were deep scratches down one long bony cheek.

Harld put the scalpel down, looking thoughtful. He paused to look around behind himself where the other two surviving members of the zoology department continued their dissection of one of the insect corpses. The body cavity was laid open, with internal organs spread out fanwise, and Bram did not care for too close a look.

“Odonata? Is that what he said?"

“Yes. Just before he died. He said it after he saw the way the creature grabbed the Cuddly, as if that had made him remember something."

“It comes from a root in a pre-Inglex language called Greek. It means ‘tooth.’ Original Man used Greek prefixes a lot in scientific classification. Ever since Jorv got back from his trip to the insect camp, he'd been poring over the old archives for insect references, especially from an institution known as the Smithsonian. But there was just so much material to absorb..."

“What does ‘tooth” have to do with it?"

“It sounds as if it may be the name of the insect order."

“Can you..."

“There's nothing to it, now. It's all alphabetical. Come back in an hour."

Bram spent the hour arguing with one of the curators from the art team, who wanted to pack an entire shuttle with a collection of paintings and photoplastic art that had been discovered at the last minute.

“It's irreplaceable,” the man pleaded. “Originals that were on loan from Earth museums. Art that was produced here on the diskworld over a period of several centuries—some of it of the very highest order. We can make a selection—let me assure you that we're prepared to be very stringent with ourselves—and have it vacuum crated within a Tenday."

Bram tried to explain that there was neither the space nor the time. “There are still crates of last-minute finds out next to the shuttle pad that are going to have to be abandoned,” he said. “Can't you make microreproductions of it?"

“You don't understand!” the curator wailed. “These are originals!"

In the end, it was decided that the curator and his staff would be allowed to take a selection of some of the smaller objects with them as their personal baggage. “The Rembrandt engravings,” the curator decided. “The little votive figurines from the Falwellite thearchy. The photoplastic diskscapes from the neo-literalist period. And some of the small table sculpture. Oh, dear, how will I ever winnow it down?"

Bram suggested that the museum staff load all the excess artwork that they could manage during the next twenty hours on one of the unused rocket-assisted pallets. Some tens of the pallets were slated to be left behind along with a lot of cargo walkers and heavy machinery. “See Jao,” Bram said. “He'll compute a rough trajectory for you. We'll have to shoot it off unmanned, but with luck, one of the interbranch vehicles from Yggdrasil will snare it and bring it in."

“B-but it could be lost forever,” the curator said. “Better to leave it here."

“No,” Bram said, looking him in the eye. “It wouldn't."

That got through. The curator nodded grimly. “I'll get moving on it right away."

When Bram returned to Harld, the thin-featured zoologist was waiting for him next to a table spread with photoplastic readouts. He handed one to Bram without comment.

Bram took the stiff sheet from him. It showed a slender, jewellike creature with bulging metallic eyes and four fragile, veined wings.

“Odonata,” Harld said. “Suborder Anisoptera. Also known as the dragonfly, or sometimes by such names as the devil's darning needle, the mosquito hawk, or the bee butcher.

Bram studied the photograph. He could see several features that suggested a possible provenance for the insect-folk: the domelike eyes, the long segmented body with the claspers at the end, the six wiry legs all grouped together just behind the head.

“Our neighbors across the plain don't have wings,” he pointed out.

“Neither did their ancestors,” Harld said. “You're looking at the adult form of the dragonfly. That creature on the dissecting table is descended from an immature form called a nymph."

Bram looked across at the grisly specimen, the liplike structure with its hooked clasping lobes was spread out to more than a fourth of the creature's body length. He shuddered.

“Dragonflies spent most of their lives as nymphs,” Harld went on. “Years, sometimes. They lived underwater, breathing through gills, eating voraciously till they grew to size. They'd attack anything that moved—creatures bigger than they were. When it came time for them to change, they'd climb up a reed, split their skin, and emerge as that glorious winged creature you see there. The adult form—the imago—was the one that reproduced. It lived only a few Tendays and died after laying its eggs."

He handed Bram another photoplastic readout. This one showed a dragonfly climbing out of a pale, cast-off ghost of itself and spreading its gossamer wings.

“What confused the issue,” Harld said, warming to his subject, “was that Odonata's like no other insect order. There was a separate evolution of the nymphal and imagal forms—probably dating back to before Earth's Carboniferous period. The dragonfly larva lacked the specialized regeneration centers—'imaginal disks,’ they're called—that in other insects formed the adult tissues from latent embryonic cells, while the larval tissues melted away. They never went through an intervening pupal stage. They changed by direct growth."

He was shoving more readouts at Bram. “The nymph adapted for an aquatic life, while the adult dragonfly remained virtually the same,” he said. “The nymph evolved independently. It developed gills. Then, at some point, apparently—like other aquatic creatures—it left the water in its immature form and developed the ability to breathe air."

Something ugly stirred in Bram's memory, the shadow of an ancient image.

Harld was trying to show him something on the autopsy table. “Jorv was perfectly right about the way they developed the equivalent of lungs. A portion of the alimentary canal just anterior to the rectum became enlarged into a sort of bellows."

One of the other zoologists, a freckle-faced fellow, grinned crudely. “What a way to inhale,” he said.

Harld looked annoyed. “It was an obvious evolution-dry step—that's where the gills were, with their ready-made oxygenating apparatus. In human beings, the embryonic gill structures are derived from the upper alimentary canal—and that's why breathing and swallowing are interrelated in us."

The shadowy memory nagged at Bram. There had been something, a long, long time ago...

Harld was saying, “So it was through these aquatic forms that evolution got around the problem of the breathing spiracles that had formerly placed limits on the size and intelligence of land insects. Plus the modification of the exoskeleton into a partially internalized support. It gave the Odonata access to the evolutionary niche previously occupied by the large mammals."

“And now they're the inheritors of the earth,” Bram murmured.

Harld frowned. “But first they had to learn how to reproduce in the nymphal stage. Without having to metamorphose into the adult winged form. Because otherwise the need to fly would have placed a limiting factor on their size."

And then Bram suddenly remembered.

“It was an unstable allele. Original Man spliced a set of synthetic chimeras into dragonfly DNA. They were trying to modify the nymph to create an organism that would keep insect pests under control in their arctic regions. They thought it would remain an aquatic form and do man's work for him. But it got out of hand."

“What?” The three zoologists gave their full attention. “Do you know something of this, Bram?"

It all came flooding back. It had been buried for almost seven hundred years in a mind that had become overlaid by other experiences. Slowly at first, then with increasing fluency, Bram told them about the synthetic heterochronic gene that had made the self-reproducing hen's egg possible—about the way a DNA chimera had been contrived out of genetic material derived from the dragonfly and the axolotl. How, generations later, Original Man had discovered the dangers lurking in the construct and had radioed a warning in a codicil to his first great Message. And how the Nar, accordingly, had suppressed the file—though it contained the seeds of man's immortality. How he, Bram, a rare human apprentice in a Nar touch group, had stumbled upon the reference and confronted his mentor, Voth, with it. How the entire Nar nation had carried their burden of guilt and finally, stunningly, made amends.

“You're saying, then, that it was the nymphal dragonflies that exterminated Original Man?” Harld asked.

His eyes were filled with horror. He was wondering, Bram knew, if it was all about to happen again.

“No, no,” Bram said. “Original Man solved the problem. Or thought he had. At great cost. The near destruction of his arctic ecology. But the mutation must just have been biding its time. It waited, buried in dragonfly nucleotides, for forty million years ... fifty million years. Long enough for the human race to go the way of the dinosaurs and to be replaced by a dominant species evolved from rats. Long enough for the rat-people to go the way of humankind—according to that timetable of periodic extinctions that your department drew up when we first arrived at the Milky Way. And when the rat-folk were gone, there was an ecological niche vacant, waiting for a new intelligent, cooperating species about the size of a man. No mammal, no vertebrate, could have competed with such as the nymphs had become."

All of them, the three zoologists and Bram, involuntarily looked over to the dissection table where the latest inheritor of the Earth lay. Harld swallowed hard.

“Man did this?” he asked.

“No, we must not be so arrogant,” Bram said. “Perhaps it would have happened without us."

Harld opened his mouth as if he were about to say something further. But at that moment Jao came bursting into the improvised morgue.

“Better come quick!” Jao panted. “They're on their way!"

“Here?"

“Yar. About a hundred of those ground vehicles of theirs. We've got to round everybody up and get out to the shuttles before we're cut off."

Bram whirled around to the three zoologists. “Get going. Put on your vacuum suits and tell everybody you see to do the same. We're going to let the air out of this place."

He turned to Jao again. “All right, let's start deputizing people. How many of those shuttles are ready to be flown?"

“Enough—if we jam them full of people and dump everything else. In a couple of hours we can strap pallet rockets to some of them. It won't take much of a boost to at least get them off the ground out of harm's way. The pilots can finish their countdowns in space if they have to."

“Good. Let's get going."

Jao was sweating. “There's more,” he said.

“What do you mean?"

“Jun Davd's been watching the ship through his telescopes. He radioed at almost the exact time our own lookouts saw the ground vehicles starting our way."

A chill ran down Bram's spine. “Go on,” he said.

“More of the environmental bubbles are detaching themselves from the stick-ship. They're just boiling off it. Drifting down to the rim of the diskworld. And some of them are heading toward Yggdrasil."