The male silth plodded forward wearily at sixty miles an hour, pausing only long enough to uproot and wolf down one of the rare scrub trees directly in its path. Its three hundred tons of massive body shook the ground as the great hind legs thumped along, and every cell of it ached with hunger. It was warm blooded, despite its vaguely reptilian appearance. Only meat could satisfy its need for energy. But the great herds lay a thousand miles to the north of this barren land.

Inside the silth, the two-pound network of converted nerve cells that was Arnek brooded darkly in self-pity and resentment against the inflexible female logic of his mate. Ptarra had won her point, as she always did; now she might at least have shown some consideration for him and his silth!

"Arnek!" The call came sharply on one of the guard frequencies of the mental spectrum. "Arnek, stop lagging and get up here!"

He could feel his nerve body tense from horn tip to tail root, but he stifled his response and quickened his pace. Ahead, the trail left by Ptarra's legs led through a gully and up a rise to the lip of a small, stony basin. The four hundred tons of Ptarra's female silth squatted below the edge and the great head was half hidden as it peered downward around a boulder.

"Quiet!" Ptarra ordered sharply. Then, as Arnek switched from a thudding run to a smooth, creeping approach, the mental impulse took on a note of triumph. "Look down there and then tell me I don't know a ship trail from a meteor!"

The bowl was bright in the glare of the orange sunlight, but at first Arnek saw nothing. Then, as his gaze swept back toward the nearer section, he blinked his great eyes, only half believing what they registered.

It was a small thing, hardly taller than Arnek's silth—maybe not even as tall. But it was too regular and obviously artificial, a pointed cylinder, to be a meteorite. Between two of the base fins there seemed to be an opening, with a miniature ramp leading down to the ground. It looked like a delicately precise model of a spaceship from the dawn of time.

It was obviously too small to be more than a message carrier. Yet, as he looked more closely, he could see motion. Two tiny creatures, not more than six feet in height, were scurrying around near the base. Bright patches of fur or decoration covered them, and they seemed to move on two of their four limbs.

Arnek shivered down the length of his nerves with an ancient distaste for crawling things. "Let's go back," he suggested uneasily. "There's nothing here for us, and I'm hungry."

"Don't be silly," Ptarra answered, and the old female superiority was strong in the thought. "Of course it's too small for us; I knew that when I saw the landing trail yesterday evening. It must be an instrument probe, with test animals. If it has telemetering equipment, though—"

Arnek tested the three spectra uneasily. At this distance, even a tight beam should be detectable. But he could feel nothing. There was only the steady wash of inertia-gravitic wavules, the electromagnetic noise from the sun and the growing, contemptuous mental leakage from Ptarra. Then he squirmed in embarrassment as his eyes detected the cracked base of the little ship.

Obviously, it had landed hard—probably hard enough to ruin instruments and release the two creatures. He should have noticed that at once.

There was no time to admit his error, however. Ptarra's silth lunged upright and the great rear legs began pulping ground and rocks in a full charge. Arnek leaped to follow out of old hunting habit. On a down-grade, his lighter silth soon caught up with the other.

Below, the two humans swung around at the earth-shaking thunder of the charge and started a frantic scrambling. They were making shrill sounds now, and the extreme low band of the mental spectrum held faint impulses.

Ptarra's thoughts lashed against his nerves. "Cut them off! Don't let them back to the probe. They may have destruct conditioning."

In the hunt, Arnek had long since become only an extension of his dominant mate. Now he folded his forelegs and dropped his head and neck into a javelin aimed between humans and ships. The smaller of the two was almost at the ramp.

At the last moment, moved by a sudden impulse, Arnek dropped his head lower and retracted his neck to soften the blow. He felt the human midge strike against his snout and go caromming off, to land fifty feet away.

Dim pain impulses stirred in the low mental background. Anger—or something like it—came from the other creature.

Arnek braked and pivoted sharply. The larger human had run forward toward the bloodied smaller figure. But as the silth's head faced the creature, one of the human's arms darted to something strapped about its middle. There was a surprising blast of sound. A stream of tiny, exploding pellets struck against Arnek's snout. He bellowed in annoyance and took a step forward, lifting a foreleg to swat at the midge.

It jerked back. Then it darted forward, bending to lift its companion in its forelimbs. Either the gravity here was less than on its home world, or the thing was stronger than it looked. The first leap sent the burdened human backwards more than twenty feet. Then it was bounding off in frantic efforts to reach the further side of the depression where a jumble of rocks might give it cover.

There was amusement in Ptarra's thoughts. "If your hunger is so great, why didn't you eat them? They aren't much, of course, but the blood smells sweet enough."

Arnek sighed along his nerves, unable to answer.

Let Ptarra put it down to another male whim if she liked, but he hadn't thought of eating them before. There had been something cute and pathetic about them. They reminded him of the little gulla he had owned in his youth, in a long-lost, ruined universe.

"It had a weapon," he commented, changing the subject.

Ptarra rumbled an assent. "I noticed. Interesting conditioning. The probe builders must have superb nerve development to do that to the lower orders. They'll make good silths.... Now let's see what we can find in the probe."

She slipped a claw into the base opening and began working it upwards as delicately as the clumsy foreleg would permit.

Arnek moved forward to help, but she waved him back impatiently, and he waited meekly until she finished. She was right, of course. As a male, he had no training with mechanisms. He would only have ruined whatever lay inside. It was a marvelously delicate set of machinery ... though the theory behind the engineering seemed rather elementary.

Arnek studied what he could of it, growing more puzzled. "Maybe the creatures operated it," he suggested.

"What makes you think so?"

"I don't know. It just seems somehow—"

"Intuition!" Ptarra snorted. Then she seemed less certain. "Yet I can't blame you this time. It does almost look that way. But it's logically impossible. Besides, there are automatic controls for guiding the probe. The builders probably just amused themselves, the way we once put slurry-pods in the gulla pens. Ah, this looks sound enough!"

She pulled a tiny box out of the wreckage that had been spread out flat on the ground.

With infinite care, she managed to hook one claw over a miniature control. Almost immediately, radio waves began forming a recurrent pattern along their nerves, coming in long and short pulses.

Half an hour later, there was another faint quiver of radio waves from space, this time completely modulated. Even Arnek could realize that it was on the same frequency, but dopplered to indicate something approaching their world. He stopped browsing for the few stunted trees and came back to join his mate.

Night was just falling. Ptarra led them back toward the rock ledge from which they had first spied the probe. There was a large fissure in the rocks into which they could just squeeze, and which would hide them from the sight of any landing craft.

A moon came up, and they could see the depression clearly in its light. Now Arnek saw the larger human slipping across the ground toward the wreck of the probe. It darted about frantically, but with an appearance of purpose. A few moments later, it was retreating, carrying a load of packages with it.

"It seems almost intelligent," he said softly.

He strained to follow the faint wash of impressions on the lower band. There was something there that struck a familiar chord in his thoughts, but he could not decode it.

"Just instinct," Ptarra dismissed it with cool logic. "A female seeking food for its injured mate."

Arnek sighed uncomfortably. "It doesn't seem female," he objected.

"Another hunch? Don't be silly, Arnek. It has to be a female. The larger, stronger and more intelligent form is always female. How else could it care for the young? It needs ability for a whole family, while the male needs only enough for himself. The laws of evolution are logical or we wouldn't have evolved at all."

There was no answer to such logic, other than the vague discontent Arnek felt. And he knew that was only because of his envy of the greater ability of the other sex. He settled back, ruminating hungrily and listening to the signal from space.

The little box from the wreck was silent now, but the other signals were stronger.

Ptarra nodded. "They're coming. After four hundred years, we have a chance. New silths to breed. A chance to reproduce ourselves and multiply. A new universe for our own." There was immense satisfaction with self in her thoughts. "Well, I earned it!"

Arnek could not deny it. It had been more than four hundred years in this galaxy. Eight thousand of them had set out, leaving behind a small, ancient universe being wrecked by the horror of an exploding supernova. They had been driven out from the planetary conquests of a billion years and had sought refuge across intergalactic space to this universe.

A hundred of the marvelously adapted silths of their universe had survived the eons of suspended animation to preserve their occupants. And then had come the hunt for new silth forms, since the trip had aged the others beyond the power of reproduction, in spite of all their precautions.

Finding a silth form was never easy. There had been only three animals that had served in their entire old galaxy. Only a creature with several pounds of nerve tissues could hold the nuclear proteins of the sentient annas. And that required huge creatures, since nerve tissue was always so thinly scattered in normal flesh.

They had toured a quadrant of the new galaxy, studying planet after planet, before they found this world. Here the great beasts were barely sufficiently endowed with nerve fiber. Eight annas had survived this far. Six failed to stand the shock of entry and regrowth in the new silth forms. Now there was only the one pair—Arnek and Ptarra.

Left to himself, Arnek would have perished long ago. Their hope of retraining the clumsy forelegs of the silth forms had proved futile, and the nerve capacity was too low for them to exercise their full faculties. The converted nuclei of the cells was never quite efficient, either. And there seemed no hope of ever reproducing their own. Certainly no newly budded anna could survive the metamorphosis into these awkward bodies; that had been almost impossible for mature powers. Nor could a young anna survive long without a silth.

Four hundred years! And now—now, he thought, he was tired. It no longer mattered. His home lay in ruins eons away. Let Ptarra worry about it. He twisted his neck back to put his snout under his tail and tried to sleep, while hunger rumbled noisily in his stomach.

The sun was glaring down again when he awoke to the nudging of Ptarra's snout, and there was a roaring in the air above. Something rushed downwards, bellowing out thrust against gravity. It was another ship, landing over the wreckage of the first.

But it was no monster such as might have carried new and better silth forms. It was hardly larger than the first, though it somehow seemed to be better made. It landed smoothly and squatted on the ground, sending out signals.

"Another probe," Ptarra said. There was disappointment in her thoughts, quickly masked by cold logic. "Naturally, they'd wait to check with something like this. There will probably be several probes before they decide they have to investigate personally. All right! We'll give them something to worry about."

She was lunging to her feet, just as an opening appeared in the ship. This time something ran out, down the ramp—a tiny gadget of churning tracks and metal carapace, chuffing out shrill little motor sounds. It circled briefly and then headed across the bowl.

"Stop it," Ptarra ordered. "It may have a camera, so don't waste time. The less the builders learn about us, the better."

Arnek took off. His hunger had so far failed to weaken him, and he was covering the ground at two hundred miles an hour before the little vehicle had picked up a tenth of that speed.

At the last moment, it seemed to be aware of him. There was a wash of mental shock and confusion. Then his snout hit the car in a sideswipe that tossed it fifty feet to land on its back. He lumbered forward to squash it, then hesitated. An opening had appeared and two of the tiny humans were staggering out. One was supporting the other. At sight of him, both stopped in shock. For a second, they stood rooted to the ground. Then the larger one began a clumsy effort at running, half carrying the other. Blood left a trail behind them.

Arnek could have squashed them with a single thrust of his leg. But he stood irresolutely, observing the garments and headgear they wore, remembering his youth and a gulla draped with a ribbon and bells. They were heading for the rocks nearest them, a long way from where the first two had found refuge. For a second, he felt impelled to turn them and drive them toward the others.

Then a wave of amusement from Ptarra checked him. "They'd never reach that far," she called. "They can't survive the crash of their vehicle. Let them go."

Arnek felt the faint, murky mental signals so low on the band, and he knew Ptarra was right. They were staggering now, and the smaller one seemed to be only partly conscious. He sighed and scooped up the ground car, carrying it back to Ptarra.

This time his mate was making no effort to rip the ship apart. She was staring through one of the tiny ports, trying to fit her great eye against it. And she seemed uncertain. Finally she took the ground car and began dismantling it, looking for automatic or remote controls.

There were none.

"Maybe the creatures operated it—and the ship," Arnek said. He expected the same reaction the remark had drawn before.

This time Ptarra showed no amusement. Her great head shook in puzzlement. "About one time in ten thousand a crazy male hunch comes true," she muttered. "Intuition! It's against all logic. But there are only manual controls here. Where are those silly creatures?"

The two that had arrived last were pitifully exposed, just within an opening in the rocks. It was a shallow space, hopeless to defend. The smaller one lay supine, but the larger human faced the two silths, holding his pitiful weapon, and waited grimly until they were almost within reach. This time the explosive pellets were aimed for their eyes.

Ptarra dropped her eyelids, swearing as the missiles stung. She reached in with a short foreleg. There was a single shrill cry and the sound of the weapon striking against a rock; the low band was suddenly quiet. Arnek heard a soft gulp. When he looked, the larger human was gone.

A sudden shock ran through Ptarra's thoughts. Her great eyes blinked and a huge tongue ran over her lips. "Nerve fiber!" Her shout covered the entire spectrum. "Arnek, there are pounds of nerve fiber in the creature! High grade—better than that in these silth forms. As good as that in any silth. Here, give me the other."

She didn't wait for Arnek's help, however. She dragged the corpse out and began working as delicately as the silth body would permit. Her mental signals were a blur. Then she stopped, staring down at what she held. "There—a cavity in the head, filled with nerve fibers. There must be three pounds there alone. What freak of evolution would put them all together in such a vulnerable spot? And yet, there's a certain efficiency about it. It isn't logical—and yet it is."

Abruptly, the evidence was gone. "Come on," she ordered.

Arnek sighed, and his stomach rumbled a protest. But he ignored it. "What good is it? We surely can't make a silth out of a tiny thing like that?"

"Why not?" Contempt for male thought was mixed with smug satisfaction for her own. "We don't use the other cells anyhow. Oh, there will be difficulties. They may be short-lived. But with such high grade fiber, we can risk infiltrating a new one as often as we need. There should be enough of them. They probably have half a dozen to a litter twice a year, like most small forms. Possibly billions of them can live on a single planet. And since they're colonizing other worlds like this one...."

Even Arnek could see the logic behind Ptarra's assumption in that. Colonizing would explain the sending out of a male and female in each ship, with ships spread out days apart. It wasn't the most efficient method, but it usually insured against any major accident. His people had used the same method at times.

It all seemed quite logical, but Arnek felt a tension of intuition along his entire nerve network. No anna had ever used a silth capable of independent intelligence. There must be something wrong with it. Once they infiltrated the new silth, of course, they could soon convert enough nerves to blank out all control from their carriers. But....

"Their weapons," he cried. "Ptarra, in those bodies, we'd be vulnerable to their weapons. And during the ten days we have to hibernate to grow into their nerves, they'd kill us."

Ptarra grunted. "Sometimes," she admitted, "you almost think like a female. They would kill us, of course, if we stupidly stayed where later arrivals could find us. Now come on. We've got to chase the creatures around today until they're tired enough to sleep soundly. And don't let them get near that ship, either!"

It was a bitter day for Arnek. His stomach protested, and by the end of the chase, his legs were beginning to weaken. But ahead of them, the two humans were staggering in the light of the setting sun. The smaller was leaning on the larger as they finally found and entered the little cave near the ship that Ptarra had chosen for them long before.

Night had fallen before Ptarra was satisfied. The two silths moved forward as softly as they could, but the loud breathing noises went on, and there was no stir of alarm anywhere on the mental band.

"Do you remember everything?" Ptarra asked. "You've got to regain consciousness after the first stage. You can do that, if you set your mind to it."

"I remember," Arnek agreed wearily. He'd had the whole routine drilled into him repeatedly until he was sick of it. It was like the horror of having her force him to adapt to this present silth. While he had been ready to accept assimilation, she had fought with him and with her own transformation, refusing to admit even his intuition that their race was ended. Only her cold logic had saved them. He could not deny it now.

"Be sure you take the smaller male body," she warned again.

"Unless that's the female. You found evolution different in these creatures once," he reminded her.

For a moment, she was silent. Then there was a mental shrug, and almost amusement as she answered. "Matching sex isn't logically necessary. It might even be an interesting amusement. But I must have the larger body."

She began shifting at once. The silth gasped and tried to thresh about in death as Ptarra released control. Arnek sighed to himself and began to follow.

It was worse than he remembered. After the centuries, the cells hated to give up their fixed form. The agony of the silth fed back to him, until his withdrawal stopped its heart. But slowly the nuclear matter flowed from the cells and up the pathways to their egress, taking the minimum of nutrient fluid with them.

It took nearly an hour, and he could see the thin film of Ptarra already lying over the sleeping human.

He began hurrying now, remembering her warning that the humans would not stay here once they wakened to find the two abandoned silths dead. He forced himself over the hateful dryness of the floor, up to the open mouth. Beyond lay the lungs, the circulatory system, and then the strange nerve bundle in the skull.

Some of it was ugly, and some was hard. But the last stage was almost pleasant. He had forgotten how unsatisfactory the nerves of the last silth had been. These were like coming home to a friendly world, in a universe that had died too long ago and far away. For a time, he was almost glad that he had not died with it.

Then the first allergic reactions began, and he had to relapse into instinct, to let his being fight to save both himself and his host cells from the reaction.

He set the first stage up, however. This time he managed with no help from Ptarra. Then he relapsed into unconsciousness, making no effort to control his new silth yet. He'd have to revise when the silth awoke, he told himself.

But it was only a dream order, half completed....

It was a sudden painful pressure of acceleration that finally brought him out of his torpor. He felt half sick, and he could vaguely sense that the new silth was fevered and uncomfortable. But, amazingly, it was sitting up. And around it was a room bigger than the whole ship had seemed, and controls under its hands, and fantastic equipment.

"It's about time," Ptarra's thoughts reached him. They were weak now, since it was hard to transmit in a partial stage, but they were cold and sure. "I've been aware for hours, while the silths reached the ship and took off. We've been off planet for at least an hour. Long enough to study their body controls and to learn how the ship operates."

Arnek sighed to himself, while the pressure of tension refused to leave. "Are you sure?"

"Of course I'm sure! These are primitive machines, and I learned most of it from dismantling the first. They're primitive—but they're logical enough for understanding. I can even control the silth when she isn't aware."

The larger human suddenly moved the controls, then jerked its hand back, staring at it. Words came to the ears of the silth in which Arnek rode. "I'm sick, Luke. I've got the twitches."

The words brought stirrings strongly on the low band, almost but not quite understandably. They also brought a vocal reply from the other human. "Be glad you can twitch. Some bug we picked up, but it's better than being eaten. We're in the clover, kid. Maybe we still got more cop ships tailing us, but let 'em look. When they find the dinosaurs and what's left of our ship, they'll stop looking. The heat's going to be off! We can get back to Earth in a year or so and really live."

Ptarra's thoughts cut through Arnek's efforts to understand. "Reproduction feelings," she reported in satisfaction. "They must have higher fertility than I hoped if they can think of it while sick." Then her thoughts sharpened. "Take over your silth!"

The human at the board slumped abruptly. Arnek lashed out from the converted cells, felt a brief protest, and then was alone in the brain of the silth.

He could not yet control it, but it had no independent will.

"There is food and water near if we have to rouse from hibernation while we grow into these silths," Ptarra reported. "Now—help me if you can."

Arnek let his weak thoughts blend into hers, trying to give strength as she had often done to him. She was straining her utmost will.

Slowly and in jerks, the arm moved across the control board, and clumsy fingers managed to move controls. And at last, from Ptarra's mind, Arnek began to see the plan.

There was fuel enough to bring them at maximum speed across an eddy of the galaxy toward the lone sun they had found long before. There a single planet swung in orbit—a planet with food but no dangerous animal life. And there they could wait and grow strong, and multiply as their silths multiplied. They could reach it almost as soon as they came out of hibernation finally, and it would be a safe haven in its isolation.

There would be no fuel for further travel. But that could wait, while their numbers grew, and they could restore their lost technology and weapons with the clever hands of the human silths. Then they could take over the galaxy—as they had taken the one so long away!

The hands fumbled under the limited control, but they moved across the board. And the automatic pilot was finally set and sealed.

"Logic!" Arnek thought softly, and there was wonder at a mind like Ptarra's that could achieve such understanding of even alien mechanisms. Yet under it there was still a cold knot of fear along his nerves.

Ptarra's thoughts had begun to fade from the strain and the long interruption to her hibernation. But now she caught momentary control again. There was appreciation in them for his praise. And then there was amusement. "Logic," she agreed. "But perhaps intuition isn't too bad for a male. You've been right twice."

"Twice?" Arnek asked. He'd been somehow right that the silths controlled their own ships, of course. But....

"Twice," Ptarra said. "I've just realized my silth is a male, as you suggested it might be. Amusing, reversing the sexes, isn't it?"

She tried to say something else, but the strain was too much, and full hibernation swept her mind away from that of Arnek.

Arnek sat frozen for a time in his silth, knowing that it was also male.

Then he turned it somehow to face the lost galaxy where his race had known its day and now entered its eternal night.