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                          THE COURSE OF LOGIC

                           BY LESTER DEL REY

                  They made one little mistake--very
                       natural--and disastrous!

           [Transcriber's Note: This etext was produced from
             Worlds of If Science Fiction, September 1963.
         Extensive research did not uncover any evidence that
         the U.S. copyright on this publication was renewed.]


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.