a zoo can be a rather depressing place, or it can be a lot of fun, or it can be so dull as to make the mind wander elsewhere in self-defense. in fairness to emeraude, robin lampert had to concede that this one was not quite in the last group. he had been able to keep his attention on the exhibits. this was, in a way, surprising; for while a frontier town has a perfect right to construct and maintain a zoo if it wishes, one can hardly expect such a place to do a very good job.

the present example was, it must be admitted, not too good. the exhibits were in fairly ordinary cages—barred for the larger creatures, glassed for the smaller ones. no particular attempt had been made to imitate natural surroundings. the place looked as artificial as bare concrete and iron could make it. to a person used to the luxuries provided their captive animals by the great cities of earth and her sister planets, the environment might have been a gloomy one.

lampert did not feel that way. he had no particular standards of what a zoo should be, and he would probably have considered attempts at reproduction of natural habitat a distracting waste of time. he was not a biologist, and had only one reason for visiting the emeraude zoo; the guide had insisted upon it.

there was, of course, some justice in the demand. a man who was taking on the responsibility of caring for lampert and his friends in the jungles of viridis had a right to require that his charges know what they were facing. lampert wanted to know, himself; so he had read conscientiously every placard on every cage he had been able to find. these had not been particularly informative, except in one or two cases. most of the facts had been obvious from a look at the cages' inhabitants. even a geophysicist could tell that the felodon, for example, was carnivorous—after one of the creatures had bared a rather startling set of fangs by yawning in his face. the placard had told little more. less, in fact, than mclaughlin had already said about the beasts.

on the other hand, it had been distinctly informative to read that a small, salamanderlike thing in one of the glass-fronted cages was as poisonous as the most dangerous of terrestrial snakes. there had been nothing in its appearance to betray the fact. it was at this point, in fact, that lampert began really to awaken to what he was doing.

he was aroused all the way by mclaughlin's explanation of a number which appeared on a good many of the placards. lampert had noticed it already. the number was always, it seemed, different, though always in the same place, and bore signs of much repainting. it bore no relationship to any classification scheme that lampert knew, and neither of the paleontologists could enlighten him. eventually he turned to mclaughlin and asked—not expecting a useful answer, since the man was a guide rather than a naturalist. however, the tall man gave a faint smile and replied without hesitation.

"that's just the number of human deaths known to have been caused by that animal this year." it did not comfort lampert too greatly to learn that the year used was that of viridis, some seventeen times as long as that of earth. for the felodon the number stood at twelve. this was not very much when compared to the annual losses from tigers in india during the nineteenth century. but this reflection was not particularly consoling. the human population of viridis was so very small compared to that of india.

lampert examined the creature thoughtfully. it was of moderate size as carnivores went—some four feet long without the tail—and looked rather harmless as long as it kept its mouth shut. it was lying in the center of the cage, so it was difficult to judge the length of its legs. it showed no trace of the tendency displayed by many captive animals, of lying against a wall or in a corner when relaxed; and there was none of the restless pacing so characteristic of earth's big cats under similar circumstances. it simply lay and stared back at lampert, so steadily that he never was sure whether or not the cold eyes were provided with lids.

"i never liked reptiles back home, but i think i like these creatures less." the voice of mitsuitei, the little archaeologist, cut into lampert's reverie.

"don't let hans or ndomi hear you mention them in the same breath with reptiles," he answered.

"well, i'm not fond of frogs, either."

"i'm afraid that wouldn't make them much happier. these are not even amphibians."

"they certainly are. i've been told that they lay eggs in water and have a tadpole stage—"

"i should have said they aren't amphibians with a capital a. that is, they don't belong to the order amphibia, since they are not genetically related to the corresponding order on earth, as far as we know. sulewayo gets quite peeved at people who try to lump terrestrial and extraterrestrial creatures in the same order. i believe that whoever decides things for biologists has decreed that on viridis the dominant order is to be called amphibids. it's a quibble, if you like. but i can see why they insist on it."

"mph. so can i. even now you sometimes run into people who go to great length to make you admit that there are pyramids both in egypt and mexico—and for that matter on regulus six—and infer from that that their makers had something in the way of common culture. i say these things are amphibians, without the capital a, because they are at home both on land and in water. and a dictionary would back me up. i don't insist that they're related to those of earth—any more than a mayan pyramid has anything but geometry in common with an egyptian one."

"but i've heard—"

"i'm sure you have, but it's a sore subject. i'll be open-minded if you like and admit that some egyptian may have been blown across the atlantic and taught architecture to the americans, but i don't regard it as proved. what was that remark of yours—'as far as we know'—in connection with the ancestry of the amphibids? that's being at least as open-minded as i was, i would say."

"in a way, yes. i don't think anyone has seriously suggested that these things originated on earth. however, a puzzle we're here to investigate still exists. how there could be life forms corresponding to those which took a good half billion years to evolve elsewhere, on a planet which by geophysical evidence hasn't been solid for forty million? someone certainly has suggested that the world was stocked from outside. but certainly it hasn't been proved. i don't think anyone has tried very hard, either. and i certainly won't, on a planet with as much radioactivity as this one."

"you think that would account for high-speed evolution?"

lampert shrugged his shoulders, and began to stroll toward the next cage. "ask the paleontologists. my opinion doesn't carry much weight."

mitsuitei nodded, started to follow the geophysicist, and then turned back to stare once more at the carnivore lying a few feet away. it stared back unblinkingly.

the visit to the zoo was one of several, which continued until lampert, mitsuitei and the two paleontologists were able to identify each of a dozen animals which were most concerned in the death rate of viridis. apparently mclaughlin was not the only guide who did this. the zoo was equipped to give a "final examination" in which any creature the guide desired could be seen on a television screen from viewpoints quite different from those obtained in front of the cages. mclaughlin proved hard to satisfy.

lampert did not blame him. he knew a lot about viridis, of course. he had not only read of it in ordinary reference material, but had done much of the laboratory work on drill cores brought from the planet. his name had been one of those attached to the report giving the probable age of the planet's crust. at that time, however, the mental picture he held had been of continent distribution, rock strata, zones of diastrophic stress and the like. the question of the appearance, or even the existence, of plants, animals and people had simply never risen to conscious level in his mind.

that had changed, shortly before his arrival. the tramp spacer which had brought him and his group to viridis had had to orbit about the world in free fall for several hours while its obsolete drive elements "cooled," and the passengers had examined the planet.

lampert, oddly enough, had been as much impressed by the night side as by the sunlit hemisphere. the latter had shown, at twenty thousand kilometers, a fairly standard land and water pattern. the most unusual thing about it had been the almost perfect uniformity of the land coloration, a light green which bespoke, or at least implied, a virtually complete covering of vegetation.

by the time the ship had circled to the dark side, however, it was much closer to the surface; and lampert would have expected to make out luminous sparks and patches of towns and cities by the hundreds.

he saw just two, and was not really sure of those. for the rest, the planet was a vast, gray-black circle occulting a portion of the milky way. it was not absolutely black, either. its contrast with the background of the galaxy was diminished by the glow in the upper atmosphere arising from the recombination of water molecules dissociated during the day by beta librae's fierce ultraviolet light. the center of the circle was darker than the edges, where the line of sight penetrated through more of the luminous gas.

but even this sight, unusual as it was, did not affect lampert as much as the lack of city lights. he had done field work in lonely, wild places before, of course; but until now he had always had the feeling of being in an island of wilderness more or less surrounded by civilization. on viridis it was the civilized spots which formed the islands. and very small islands they were. there was no known native intelligent race, and settlements of alien races such as the men from earth were still few and far between.

so lampert was prepared for mclaughlin's care in readying the group for its trip. he was even glad of it, though he would probably not have admitted to being at all afraid of the venture. he would simply have said that it was nice to have a guide who took his responsibilities seriously.

that of course, did not mean that lampert was intending to disavow any of his own responsibilities. he, like mclaughlin, had been keeping a careful eye on the other members of the group, looking for the signs of impatience or ill temper which could be the seeds of serious trouble if the journey were prolonged. he had come to tentative conclusions about this during the flight from earth, but was pleased to see that, apparently, men who could stand the enforced companionship of a tramp spacer were also able to retain their senses of humor in the steam-bath environment of viridis.

sulewayo, of course, had seemed safe from the first. a man who has spent his formative years in the congo rain forests where his ancestors had lived for generations was ideal for this world. his sense of humor was extremely durable. lampert suspected that it might sometimes be a little too good. mitsuitei, the archaeologist, had once or twice appeared to resent some of the young fellow's remarks, though not to an extent where lampert had felt the need for introducing his own personality into the matter. krendall, nearly twice sulewayo's age, seemed to be a check on the younger man anyway; he was a member of the same profession, and sulewayo would have been the first to admit his respect for krendall's work in the field. under the circumstances, lampert felt that the group was well matched.

whether it would be able to do the job it had undertaken was another matter. the news reports had spoken glibly of the expedition which was going to "solve the mysteries of viridis once and for all." lampert, like any other scientist, knew perfectly well that the solution of the present crop of mysteries about the planet would almost certainly be achieved only at the cost of creating an even greater number of new ones. even the guide, who was admittedly no scientist, had expressed a similar opinion, though his was based on a general pessimism bred of familiarity with the planet. however, he had undertaken to get them to the sort of country they wanted; and from then on the problem solving was not his affair.

the scientists, whatever may have been their feeling about matters of personal safety, were eager to start, which tended to cause rapid progress in mclaughlin's animal recognition school. another factor tending toward the same result was that there was little in emeraude for such men to do, except learn. the town was still small. it had a spaceport and airport, which furnished little entertainment, docks which could amuse for a while but not indefinitely, and warehouses which were completely uninteresting to geologists, paleontologists and archaeologists. there was no museum. the numerous specimens of mineral, animal, and vegetable matter collected on the planet invariably wound up on outbound spacecraft. the zoo, which the town maintained for purely practical reasons, was about the only thing that was left.

in consequence, not many days passed before all four scientists were able to meet mclaughlin's requirements. sulewayo was annoyed by the guide's addition of a short postgraduate course in edible flora and fauna, but admitted that the knowledge might well be useful. however, he made no secret of his satisfaction when mclaughlin finally announced that, as far as he was concerned, the journey could begin at any time.

all four rechecked their equipment—that of lampert was by far the bulkiest—and, everyone satisfied with the group's ability both to live and to work in the steam bath that was the world of viridis, they watched the harbor on which emeraude was located shrink and blend into the rest of the shoreline behind them. within a few minutes only the restless surface of green bay was visible through the ever-present haze....

the jaws of the felodon abruptly stopped moving and its forelegs straightened, bringing the fanged head up and away from the kill it had just made.

if a man had been there he would neither have seen nor heard the disturbing factor, for a thunderstorm a few miles to the west was emitting an almost continuous growl and the towering trees shut out nearly all the sky. nevertheless the beast appeared to sense something out of the ordinary. it twisted its short but supple neck ceaselessly, rocking its head from side to side to bring first one eye and tympanic membrane to bear on the jungle roof, then the other. sometimes it froze motionless for a long moment, and a watcher would have sworn that its minute brain was struggling with a thought. if this were the case, the thought must have been both unusual and unpleasant, for under normal circumstances nothing short of overwhelming force would have driven a felodon from its meal. now, however, the hind legs slowly straightened and the creature came erect. for another moment it stood motionless, took a step or two away from the body, and stopped again.

abruptly, as though in defiance of some impulse, it turned back, lowered the murderously armed head and tore a huge mouthful of flesh from the carcass. then, like a child leaving the cookie jar as its mother approaches, it leaped away into the underbrush, still swallowing.

its speed was high and it did not have far to go. the jungle thinned in a few hundred meters to the point where some sky became visible, and a short distance further the riotous plant growth vanished completely to give place to an open beach. here the creature stopped and repeated its search of the hemisphere overhead.

this time it found what it sought.

along the line of the beach, perhaps a kilometer out to sea, the thing came flying. it must have been utterly different from anything the felodon could ever have seen, but no sign of fear appeared in the beast's demeanor. it stood on the beach, well away from the shelter of the jungle and certainly in full view from above, its head following the flying object and a fearful snarl—which might or might not have been its normal expression of hunger—giving its face an almost mammalian cast.

this thing was larger by far than any flying creature the felodon knew—incomparably larger than the felodon itself. its details were hard to make out through the hazy air, and would have meant little to the flesh-eater in any case. the most noticeable characteristic was the steady, whistling hum that proceeded from it. there was a suggestion of motion, too, which might have been wings or might not. actually, the thing was little more than a dark dot against the purplish-blue sky. at the moment no sunlight was striking it directly, for it was in the shadow of the thunderhead. perhaps this prevented the animal below from being bothered by another unusual feature it possessed, though even the appearance of this last characteristic produced no sign of fear when it finally came. this occurred shortly after the flying thing passed, while it was still quite close. it moved out of the shadow of the great cloud and, as the greenish sunlight struck it, the eyes of the watching creature were dazzled by a gleam of metal.

this was certainly something it had never seen, for native metal on viridis is just about as common as it was on earth before men began to pry it out of its ores. viridis has an oxygen-rich atmosphere and plenty of moisture, and pure aluminum or chromium just doesn't occur in that environment.

strange or not, however, the gleam did not appear to affect the felodon's rudimentary sense of fear. for just an instant it paused as the flying thing hummed on into the northeast; just once it looked back toward the point in the jungle where it had left its kill—a point from which eloquent sounds were now coming, betraying the presence of carrion-eaters; just one step it took in that direction. then it turned away as abruptly as it had from the meal a few minutes before. with the same purposeful air it had displayed on the way out of the jungle it headed down the beach in the direction taken by the flying piece of metal.

though the animal's speed was high, the humming soon faded out ahead of it.

however, this did not seem to cause any inconvenience; the felodon moved on, with a gait that might have been called a fast walk or a slow run, never hesitating, never pausing. it remained silent. smaller creatures which might have given it a wide berth had they heard the hunting call now sprang away almost from underfoot. it paid them no heed, but continued on its way while the green sun settled into the jungle behind and to its left. the fact that its recent kill was now little more than a skeleton did not seem to bother it. perhaps it had forgotten.