THE VETERINARIAN APPROACHED CAUTIOUSLY AS the bongo watched warily.

The vet, Lyndsay Phillips, wore jeans, sneakers, a turquoise sport shirt and a ratty brown National Zoo jacket. He was armed with a pole tipped with a needle full of anesthetic. The bongo, a 16-month-old male named Nekuru, was a 350-pound African antelope with white pin stripes running up his brown coat, and a ridge of spiked hair sitting along his backbone like a punk-rock haircut. He was armed with two foot-long horns.

Soon, Nekuru would be moving to a zoo in New Orleans, where he would begin a pleasant career as a stud. But first he had to get his "50,000-mile checkup" -- a TB test, hoof check, vaccinations and various blood tests. Which is why he'd been lured from his pasture, isolated in a little room and given no food for 24 hours. And why Phillips had opened his door and was approaching, slowly, cautiously, carrying his drug-tipped pole like a spear.

"Hi, guy," he said softly, soothingly. "How are you?"

Then he lunged forward and speared Nekuru in the rump. The bongo jumped and Phillips leaped back. He shut the door, bolted it and watched Nekuru through a wooden window he'd propped open with a sweet potato.

"He's calm," Phillips said to veterinary resident Jackie Dziarski, who recorded that information on a form she carried on a clipboard.

Inside, Nekuru was getting groggy and starting to wobble. This was a perilous moment, when the bongo could fall, possibly pull a muscle or break a leg. So Phillips and keeper John Hough tiptoed into the room and held him, Phillips in front, holding the horns, Hough in the rear. Phillips, 40, stripped off his zoo jacket and wrapped it around Nekuru's head to keep out distracting visual stimuli. Suddenly the bongo surged forward. "Close the door!" Phillips yelled, as he hung on to the horns, riding the beast across the room like a rodeo clown.

But Nekuru's strength was fading. The two men held him for a few minutes, then eased him gently to the floor. As Dziarski knelt to take tubes of blood from a vein in the bongo's neck, Phillips braced the animal's head against his thigh, and Nekuru, now unconscious, made slow, sleepy sucking motions with his lips, like a human infant dreaming of its mother's breast.

AT THE ZOO, THERE ARE MARVELS AS BIG AND BLATANT AS an elephant and wonders as subtle and unseen as the dreams of a bongo.

The zoo is a place familiar to hundreds of thousands of Washington residents and visitors from around the world, who growl at the lions, and ape the apes, and say "Cute!" or "Gross!" in a variety of languages. It is also a place unknown to everyone but its employees, who cook the animals' food, fix their teeth, study their sex lives, test their urine for signs of pregnancy, chase them when they escape, perform autopsies on them, cremate them, and who are, on occasion, attacked by them.

The National Zoological Park is a place teeming with life -- 163 acres inhabited by roughly 5,000 animals of about 500 species. Nobody knows exactly how many animals live there because birds and bullfrogs frequently move into the wetlands exhibit unannounced, and little creatures without backbones frequently hatch from hidden eggs in tanks in the Invertebrate House and suddenly appear, crawling up the glass as if they owned the place.

The zoo is a place of things unnoticed. It is the home of a monkey whose paw was bitten off by a gibbon; a lizard who lives in the bat cave; and a flock of butterflies with numbers written in Magic Marker on the underside of their wings. It is the residence of a tiger who likes women but scorns men; a spider monkey who gets a daily dose of Digoxin for his heart disease; and several female orangutans who were given human birth control pills, which failed to control birth.

The zoo is a menagerie in living color -- home of the red kangaroo, the green-winged macaw, the crimson-rumped toucanet, the black-and-white colobus, the blue-gilled angelfish, the purple sea star, the turquoise tanager, the pink-backed pelican, the crimson anemone and the Caribbean flamingo, which keeps its famous pink color in the wild by eating shrimp, but in the zoo, where its diet is less ritzy, is fed a red dye that produces the same effect. But only red dye works: Green or purple dyes, like no dye at all, would yield only a pale white flamingo.

The zoo is a little metropolis, a socialist city of 340 workers -- plumbers, electricians, welders, doctors, research scientists, all of them employees of the federal government -- and a captive population that does no work at all yet still receives free food, housing and federally funded medical care from cradle to grave, or, more accurately, from incubator to incinerator.

The socialized medical system is headquartered in a modern veterinary hospital that includes an intensive care unit, an X-ray room, an operating room and a collection of dental tools that enabled Phillips to perform a double root canal on a tiger who chipped his teeth on a chain-link fence. There is also a computer, which stores the medical records of every animal in the place; special deep freezers, which can store animal sperm and embryos for hundreds of years; and a colonoscope that can show the inside of animal intestines on the hospital's closed-circuit TV system.

Despite all the state-of-the-art equipment at their disposal, the zoo's veterinarians don't get much respect from their patients, who tend to remember these skilled and dedicated healers only as humans who jabbed them with needles or shot them with blow darts that made them groggy and pass out. Consequently, the arrival of a veterinarian causes monkeys to flee, birds to fly, tigers to growl and gorillas to throw the most disgusting substance they can find in their cages, which are not equipped with flush

toilets.

Gorillas, who are 98.3 percent genetically identical to humans, according to recent research, are the Nolan Ryans of feces-flinging, fastball artists with amazing accuracy. Which is one reason why zoo vets, like zoo keepers, tend not to wear fancy clothes at work.

"I'M NOT FLUENT IN GORILLA, BUT I SPEAK ENOUGH THAT I can use it to let them know how I'm feeling," Melanie Bond says. She is standing in the walkway behind the gorilla cage and poking a twig through the wire mesh to scratch Nikumba, 36, the oldest male gorilla in North America, who was enjoying the attention. "When the vets come in, I can reassure Nik with a pleasure rumble that 'Okay, it's all right, they're not coming for you.' And if {the animals} are misbehaving -- if they've done something I'm really upset about -- I threat-bark at them."

Bond, 39, has been working with apes at the zoo since 1975. Back then, zoo keepers, ignorant of gorilla sociology, hand-raised apes and housed them alone, which resulted in a lot of gorillas too neurotic to breed. Since then, research by Dian Fossey and others has shown that wild gorillas are social animals who live in extended families. Now, Bond and the other keepers in the Great Ape House are working to create an artificial extended family out of five gorillas recruited from various zoos.

"We have an adult male, an adult female and three young animals," Bond says. "It looks like Mommy and Daddy and three kids, but nobody is related to anybody else."

The patriarch of this experimental family is Tomoka, 28, who was born at the zoo, raised in the head keeper's house, dressed in diapers and taken on trips to the supermarket -- facts that make Bond cringe today. In 1985, Tomoka was slowly introduced to Kuja, a 2-year-old male, and Mandara, a 3-year-old female, both of whom had been sent from a zoo in Milwaukee. Later, the group was expanded to include Mesou, now 35, a wild-caught female who'd bounced from zoo to zoo, branded as grouchy by keepers everywhere, and a young male named Gus, now 8, an adolescent who reminds Bond of a teenage boy. "He's so busy trying to show how cool he is," she says. He does it by picking on his "little brother," Kuja, by strutting his stuff for the public, and by leering lustfully at some of the female humans who volunteer in the ape house. He has also begun mating with Mandara, and Bond hopes to see a baby born into the group in a couple of years.

So far, this experimental family appears to be getting along fairly well. "It doesn't function as smoothly or naturally as a true gorilla family would," says Bond, "but I don't think anybody can say exactly how a normal gorilla family functions."

Bond sees herself as a sort of foster mother to the group. "I think I have the best of all possible worlds," she says. "I don't have to contribute anything to the financial support of these kids. I don't have to worry that they'll be running around the streets doing drugs. I don't have to argue with them about what clothes they'll wear to school. I don't have to save money for college. And my folks live in suburban Maryland, so they come here to visit their grandchildren."

AT THE ZOO, THE COMMISSARY IS A CORNUCOPIA OF ODD edibles.

The warehouse holds huge sacks of "Rodent Laboratory Chow," and "High Protein Monkey Chow," cases of "Zu/Preem Primate Diet," and cans of something called "Eubilac Liquid," billed as a "replacement for bitches milk." The walk-in freezers are stocked with horse ribs, ground-up eggs, frozen butterfish, "Nebraska Brand Bird of Prey Diet" and bags of dead baby mice, which are known as "pinkies" and eagerly eaten by almost everything from leopards to egrets. There's cricket meal to feed the crickets until they, in turn, are fed to birds or monkeys or lizards, and there are baby chickens that chirp away until they're gassed with carbon dioxide and delivered to the crocodiles and the wolves. There's also plenty of food you could take on a picnic -- apples, oranges, peanut butter, honey and Wonder bread. And all of it is delivered daily to the animals' doors by Wayne "Joy" Johnson, who moonlights in a rhythm-and-blues band and once sang with Dionne Warwick.

At the zoo, animals eat strange stuff. Some birds devour pinkies, peanut butter and "Grand Gourmet Dog Food," though not necessarily in the same meal. Lions and tigers gorge on beef all week and fast on Sundays, when they gnaw rib bones to clean their teeth. Every day, an elephant consumes two bales of hay, 10 pounds of herbivore pellets, five pounds of carrots, five pounds of apples, three pounds each of sweet potatoes, oats and bran, plus a few tree limbs. Monkeys eat cooked beef, live crickets, sunflower seeds, raisins, peanuts, popcorn and a special vegetable of the day. Every morning, they also get a chewable children's vitamin pill.

Worried about cholesterol, zoo keepers have cut back on the eggs, milk and meat in the gorillas' diet and started serving baked fish garnished with orange slices -- a recipe included in the zoo's Great Ape Cookbook, which was distributed at a gorilla conference in Columbus, Ohio, this month.

Coral live on leftovers. Every once in a while, their keepers in the Invertebrate House collect various items -- fish, plants, a stale sandwich, an unfinished Coke -- whirl them up in a blender, pour the resulting mix into an ice tray, freeze it and then drop a cube or two into the coral tank. And the coral -- hungry little polyps that are animals, not plants -- slurp it right up.

Snakes and lizards eat mice and rats, which can create quite a scene. As keepers toss dead rodents to hungry reptiles, wide-eyed zoo visitors gather to gasp or shriek or giggle or cheer or say, "Gross!" -- but they seldom avert their eyes from the spectacle. Occasionally, Dale Marcellini, the curator of herpetology, gets angry letters from visitors who argue that it is immoral or disgusting or cruel to feed animals to animals who eat animals.

"What do they want us to do?" he asks rhetorically. "Feed them rat-shaped tofu?"

PEOPLE SMIRK ABOUT ROBO-BADGER. THEY SNICKER ABOUT Robo-Badger. They laugh out loud about Robo-Badger. And with good reason. Robo-Badger is, after all, a dead badger mounted on a remote-control toy truck, which is kind of silly. But it is also a symbol of just how far the people at the National Zoo will go to save endangered species -- even an endangered species of wretched, rotten little brutes.

Robo-Badger does its laughable, laudable work at the zoo's Conservation and Research Center in Front Royal, Va., a 3,150-acre breeding range for exotic and endangered species. There, in beautiful pastures on the slopes of the Blue Ridge Mountains, live herds of endangered animals -- Pere David's deer, a Chinese species now extinct in the wild; Przewalski's horse, the Mongolian species once ridden by Genghis Khan; the Persian onager, a wild ass now nearly extinct in its native Iran; and the scimitar-horned oryx, which looks like a unicorn with an extra horn. Inside, in the center's Small Animal Facility, are breeding programs designed to save such endangered species as the golden lion tamarin, a Brazilian monkey; the tiger quoll, an Australian marsupial; and the Guam rail and Micronesian kingfisher, two birds now extinct in their native Guam.

And then there's the black-footed ferret, the beast that brought Robo-Badger to Front Royal.

The black-footed ferret is a spouse-abusing, home-invading brute that eats prairie dogs, which are, according to a sign at the zoo, lovable creatures who greet each other with a kiss. In contrast, the ferret, says researcher Brian Miller, "is sort of the ultimate unwanted guest: It moves into the burrow, eats the dog, stays overnight."

Despite that fact, Miller, 42, is working tirelessly to save the black-footed ferret, which is now extinct in its native habitat, the Great Plains. It is not an easy task. Back in 1985, there were only 10 black-foots left in the world, and two of them were sick. Now, there are more than 100 adults, many of them in Front Royal, where their nest boxes are monitored by remote-control TV cameras so biologist Larry Collins can watch them breeding. It's not a pretty sight. "They're really rough," Collins says. "You see a male drag in the female, looking like it was a rat he killed and is going to eat."

Despite the presence of human voyeurs, the ferrets are breeding so well that they're scheduled to be released into the wild next year. Which presents a problem. All these ferrets are captive-raised. They've never learned how to avoid the owls and badgers that hunt them. So Miller has to teach them those skills. To do it, he got the carcass of an owl, had it stuffed and hung it on a pulley that enables it to swoop menacingly down on the ferrets. Then he got a badger who'd been killed by a car in Wyoming and had it flown to Virginia, stuffed by a Smithsonian taxidermist and mounted on a Radio Shack remote-control toy truck so he could send it zooming after the ferrets.

But there was another problem. These predators, being dead, cannot do much damage to the ferrets. Consequently, the ferrets are liable to get the mistaken idea that owls and badgers are harmless. So when Miller sends in his predators, he also shoots rubber bands at the ferrets with a plastic gun he purchased at a toy store.

So far, the training program is working well, and now Miller is considering the next step -- putting a real owl in with the ferrets. But first, he'll have to blunt the owl's talons to prevent it from killing slow learners. "Either that," he says, "or give the ferrets a little flak jacket."

He's kidding about the flak jacket. At least he seems to be kidding. It's hard to tell. People who will put TV cameras in ferret nests and mount dead badgers on toy trucks just might put a flak jacket on a ferret.

AT THE ZOO, THE GIANT PANDAS SPEND MOST OF THEIR TIME either sitting on their butts eating bamboo or passed out in their cages, sleeping it off, while human primates gather outside to watch and say, "Oooooo!" and "Aaaaaaah!" and "They're soooo cute!"

Which shows that both species are just doing what nature demands of them.

Pandas are fated by geography to live on bamboo, which has few nutrients. Consequently, they must spend hours eating enough of it to sustain life and more hours resting while their stomachs wrestle with the nearly indigestible fiber.

Humans, meanwhile, are biologically programmed to go gaga over animals that have facial proportions similar to human infants', according to a theory advanced by Konrad Lorenz, the famous Austrian ethologist. Consequently, pandas -- with the big eyes, high foreheads and button noses of a classic baby face -- cause poor, defenseless humans to grin idiotically, go kitchy-koo, snap out-of-focus pictures and generally behave like giddy new parents.

This behavior is a godsend for the zoo's souvenir stands, which sell thousands of panda buttons, panda pens, panda spoons, panda postcards and panda T-shirts every year. Still, it kind of irks zoo director Michael Robinson, who prefers red pandas to giant pandas and who once went on TV to electronically erase the cute black circles from around the eyes of a picture of a giant panda. "It instantly became evil-looking," he says.

Ironically, Ling-Ling, the female panda and international cuteness symbol who has drawn so much public sympathy for losing five babies, is about as cuddly as a piranha, according to those who know her best.

"She's nasty," says her keeper, Edwin "Jake" Jacobs.

Jacobs, 58, ought to know. A few days before Christmas 1984, he stepped into her cage to remove a bamboo stick that was preventing the door from closing, and Ling-Ling, who had been snoozing in her yard, leaped up, ran faster than anybody thought she could and knocked Jacobs down. Then she gnawed on his leg, clawed his back, chewed on his neck and literally bit the hand that had fed her five days a week. She probably would have killed him too, if another keeper hadn't helped him to get away.

Why did she do it? "She didn't want me in that area," he says. "It was her first chance to get me." Like most zoo keepers, Jacobs is reconciled to the fact that the animals he serves would kill him if they got the chance and would suffer not a moment's remorse.

"But you can't tell the people that," he says. "They say, 'That cute little teddy bear! How cute she looks sitting in the corner!' And if you tried to explain to people, they wouldn't believe you. So I just don't say anything."

As he speaks, Jacobs is standing at Ling-Ling's door, right at the scene of the attack. He looks at his watch. It is almost 11, feeding time. "Ling!" he yells. "Ling! Come on, Ling!"

She ignores him, staring right through him like she'd never seen him in her life. He shrugs and goes off to fetch her some bamboo.

LYNDSAY PHILLIPS KNELT DOWN IN THE STRAW AND STUCK A hypodermic needle into the bongo's back.

The beast didn't budge. Nekuru was completely unconscious now. Phillips picked up each foot and inspected the hooves. Then he put on a stethoscope and knelt over Nekuru, listening to his heart, first on the right side, then on the left.

"I hear a murmur on this side," Phillips announced. He stood up, his stethoscope danging from his neck. "It continues all through the heart cycle, but I only hear it on one side."

The murmur was probably caused by the awkward position the bongo was lying in, Phillips said. So he decided to move Nekuru to his right side and see if it went away.

With the help of two keepers, Phillips rolled the 350-pound animal over. Then he knelt down again, held the stethoscope to the bongo's chest and listened.

"All better," he said.

Phillips and the keepers rolled Nekuru back on his belly, then gathered up their equipment and the six tubes of blood they had taken from Nekuru's neck for testing, and started loading it into their truck. Before they left, Phillips took one last look at the bongo, peeking through the window that he'd propped open with a sweet potato. Inside, Nekuru was waking up. Phillips and keeper Al Perry watched as he staggered to his feet and took a few groggy steps.

"I never saw you take so much blood from an animal," Perry said.

"He'll die of blood loss tonight," Phillips replied, deadpan.

"I'll call the People for the Ethical Treatment of Animals," Perry said, grinning, "and give 'em your name."

Phillips laughed, tossed the sweet potato to Perry and went off to pay a house call on a crocodile.

AT THE ZOO, SOME ANIMALS TRY TO SNEAK IN AND OTHERS try to sneak out.

Migrating ducks and geese frequently stop at the wetlands exhibit for free food and sometimes stay to mate with the residents. The ponds also attract crows who enjoy eating the birds' food, and foxes who would prefer to eat the birds themselves. One night, a raccoon ate several red-breasted geese, which cost $1,800 apiece, while ignoring the more prosaic $20 birds in the same enclosure. Years ago, dogs broke into a yard and killed an antelope. And one night, a human intruder shot and then stabbed a wolf.

Sparrows and pigeons flock to the zoo in such large numbers that employees are sometimes sent to shoot them with pellet guns. Mice live hidden in the nooks and crannies of the monkey house, where they eat the monkeys' food and are occasionally eaten by the monkeys. The keepers set out traps baited with poison pellets called Vengeance, which kill mice but not cockroaches, who love the stuff and grow big and strong on it. "We have the biggest cockroaches you've ever seen," says collection manager Lisa Stevens.

Some animals are even foolish enough to move into the tiger yard. A couple of ducks tried to raise a family in the tiger moat, but they soon became snacks. And a pair of pure-white wild squirrels lived near the tiger yard for a while, but no more. "One day," recalls Robinson, "there was only one, and some bits of white fur were in with the tiger, who must have had one of its most exciting days in a long, long time. And there were these little feet . . ."

At the zoo, employees enjoy tales of unauthorized entrances, but they really love telling stories about escape attempts. Like the story of the Malaysian sun bear that broke out and high-tailed it to the parking lot, where he was shot with a tranquilizer dart and recaptured. Or the two pythons that were fighting so intensely over a rat that they rolled out the back door of their cage and tried to squeeze each other to death until they were hosed down by a keeper. Or the Abyssinian ground hornbill that escaped from the bird house so many times that he earned the nickname "Houdini." Or the Reeve's muntjac, also known as a Chinese barking deer, that bolted down Connecticut Avenue before he was captured in a back yard in Cleveland Park. Or the Barbary ape named Chuck who leaped off the waterfall on Monkey Island, flew over the moat, cleared the guardrail, landed in a baby stroller and sprinted to the basement of the zoo restaurant, where he was captured in a storeroom.

And there's the now-legendary story of the great orangutan picnic.

Surrounding the orangutans' yard is an electrified "hot wire," designed to keep the apes inside. When it's working, the wire emits a clicking noise, but one Saturday in the spring of 1988, it wasn't working. Bonnie, a 170-pound orangutan, apparently noticed that one wire was not clicking and decided to go AWOL. Carrying her 6-month-old baby, Kiko, she climbed up on a barrel, stepped over the wire and perched in a patch of pansies.

Somehow, she acquired an Igloo cooler and began eating chicken and drinking Coke.

Two other orangutans, Azy and Indah, climbed out and joined the picnic, but Indah's brother, Tucker, stayed behind, screaming hysterically until his sister returned. That left Bonnie, Kiko and Azy still outside when the vets arrived. Azy took one look at them and jumped back into the yard. But Bonnie, still carrying Kiko, climbed up on the Ape House roof.

"By this time," recalls Melanie Bond, "she'd had her beverage and her main course, and so they put bananas in the yard and she came down, got the bananas and came inside." "RIAU!"

No answer.

"Reeee-owwww!"

No answer.

Lisa Wilson stands at the reinforced metal door that leads to the tiger yard, calling Riau, a 245-pound Sumatran tiger, to lunch. She shakes her keys and bangs on the door and calls again, but Riau merely yawns. He is lying on the highest level of the yard, stretched out in all his fiery glory and, although Robinson frequently warns against anthropomorphizing -- assuming that animals think like humans do -- Wilson can not help concluding that Riau is enjoying the sunny, hot day and doesn't want to come inside, even though it is air-conditioned in there and it is time for lunch, which consists of five pounds of chopped beef topped with a huge rib bone.

"He's sitting up there saying, 'Nope, I'm not ready,' " she says.

So Wilson, 25, eats her own lunch -- McDonald's fries -- and does some chores, and then reassures Kerenci, the female Sumatran tiger, that, yes, she will get to go outside soon. Kerenci and Riau are fiances of a sort: She was imported from Indonesia to mate with Riau. But not yet. For now, the two are kept in separate cages -- with a barred window between them -- and never released into the yard at the same time. If Kerenci were to get her turn in the sun, Riau would have to be coaxed inside.

"Riau!" Wilson yells, banging on the door again. Then she notices Riau standing right below the window, waiting patiently for admittance. "There he is," she says. "God, he's so cute."

She pulls hard on the rope that raises the heavy steel door to the yard. Riau strolls into the wire-mesh tunnel that leads to his cage, his muscles rippling under his magnificent striped coat.

In his cage, he goes right to the window he shares with Kerenci. She is waiting there, and they rub heads and French-kiss through the bars for a moment. Then Riau goes off to eat lunch, and Kerenci bounds down the tunnel and out into the yard.

Outside, she pauses, as if stunned by the bright sunlight. Suddenly, a little black bird swoops down like a dive bomber, pecks Kerenci on the back and quickly flies to the branch of a nearby tree.

"I've never seen that before," Wilson says.

The bird swoops down again, pecks Kerenci on the back and zooms back to its perch.

Kerenci looks confused.

Then the world's bravest, craziest or most foolish bird attacks a third time, pecking the tiger on the rump, then fleeing to the safety of its tree, where it chirps happily as if to inform its drinking buddies that it has just won the bet.

"This," Wilson says, "is unbelievable!"

AT THE ZOO, THE RESIDENT SCIENTISTS ARE CONSTANTLY studying the resident animals and publishing their findings in scholarly articles titled "Social and Sexual Behavior of the Rufous Elephant-Shrew in Captivity" or "Seasonal Variation in Use of Time and Space by the Wedge-Capped Capuchin Monkey" or "Regurgitation in Gorillas: Possible Model for Human Eating Disorders" or "Capillaria Hepatica in Kirk's Dik-Dik."

About five years ago, Dale Marcellini was sitting in his office at the Reptile House, thinking about what animals he'd like to research. He wanted to go to the tropics and study lizards, but he didn't have the time or the money to do that, so he was sitting there, morose, until suddenly it hit him: Why not study the visitors?

What an idea! Zoo visitors are bizarre bipeds, frequently clad in garish T-shirts, who wander aimlessly, grazing on hot dogs and ice cream cones, then suddenly turn without warning and snap pictures for no apparent reason. Visitors spend 20 minutes watching Melanie Bond clean gorilla cages and then leave when she lets the gorillas in, causing her to say, "Wait, the good part's just starting." Visitors toss strange totemic objects to the animals -- a tennis ball, a rubber crocodile, a baby bottle, a beer bottle, a stocking, a package of chopped meat and a book titled Personal Bible Verses: Comfort, Assurance, Salvation. Visitors watch tigers and argue over who would win a fight between a tiger and a gorilla; or they watch gorillas and debate the merits of the theory of evolution:

Woman: "It's a bunch of bunk!"

Man: "It's only bunk if you don't believe it."

Woman: "You can't make a human from an animal."

Man: "Sure you can, but you need a million years."

Marcellini, 53, decided to do a "tracking study" of visitors to the Reptile House. "We basically identified focal animals at random as they entered the building and then we noted, if we could, the sex of this beast," he recalled wryly in a recent speech to the American Association of Zoological Parks and Aquariums. "We then tracked them around the building, and recorded what exhibits they stopped at and how long they spent at them."

The results were disappointing, to say the least. The 573 tracked visitors spent an average of 14 minutes in the Reptile House, where they looked at each of Marcellini's painstakingly constructed exhibits for approximately seven or eight seconds. Results were strikingly similar for all ages and sexes, with a couple of exceptions: Females and couples spent more time watching eggs hatch while males -- particularly teenage males -- prefered ogling poisonous snakes.

In his article, "Visitor Behavior in the National Zoo's Reptile House," published in Zoo Biology magazine, Marcellini reached a depressing conclusion: "Our visitors may not be interested in the exhibits."

Why not? "People say they visit zoos primarily to be with family and friends," Marcellini said in his speech, citing surveys of zoo visitors. Then he added a laconic afterthought: "Although they also mention animals on occasion."

Marcellini may sound a tad cynical about zoo visitors, but he's also hooked on the subject. He's currently working on a study that tracks visitors around the entire zoo. "We know more about lizards than we do about visitors," he says. "It's frightening. They're the only animals here that we know nothing about."

IN THE ZOO'S PATHOLOGY DEPARTMENT, THE CONFERENCE room is decorated with large, framed photographs -- multicolored abstract pictures full of slashes and splashes and swirls. One of them looks like the inside of a pomegranate. It isn't.

"It's actually a staph infection in a bird's brain," says veterinarian Richard Montali.

Montali shot the picture with a camera mounted on his microscope, then had it enlarged, framed and hung on the wall. He shot all the other pictures the same way. "They represent various disease states," he said, "but if you look at them, they also have art value to them."

Montali pointed to the next picture. "This is a structure from a fungal infection in a duck," he said. "You have to admit that has some artistic quality."

Montali, 51, is head of the zoo's pathology department, which performs medical tests on living animals and autopsies on dead ones. In his 15 years at the zoo, Montali has done autopsies on just about everything from cockroaches to elephants. He's also a kind of medical detective, seeking to identify an animal's killer before it strikes again.

One of his toughest cases began in 1982, when reindeer at the Front Royal center began exhibiting strange symptoms. First, their legs began to wobble like a drunk's, then they gradually became unable to stand and finally they died. Soon, other animals -- including rare and expensive sable antelopes -- devel- oped the same symptoms. What was causing them? Montali wondered. Toxic plants in the pasture? Deficiencies in the diet? Parasites?

After much study, Montali located the culprits inside tiny cross sections of the animal's brains and spinal cords -- they were "brain worms," a parasite commonly found in wild white-tailed deer, which are numerous in Front Royal. In deer, the worms are harmless. But in reindeer, antelopes and similar animals, they short-circuit the spinal cords, causing slow death.

Obviously, the deer would have to be fenced out of the reindeer and antelope pastures. But there was, Montali knew, another complication: Snails and slugs can pick up the tiny brain worms from deer feces and carry them into the fenced-off pastures. So the folks at Front Royal built snail and slug barriers. And then the plague ended.

Today, that case is commemorated in a photograph on Montali's conference room wall. It's a beauty -- two colorful swirls that look like twin sunbursts or a pair of cat's eyes but are, of course, neither. They're cross sections of the innards of the brain worm inside the cranium of a sable antelope.

Montali gazes at it with pride. "You don't have to be a pathologist," he says, "to see that there are some modern art qualities to these things."

AT THE ZOO, DEMONSTRATORS FROM PEOPLE FOR THE Ethical Treatment of Animals gather every Christmas to bring nonalcoholic champagne for the zoo keepers and fruit and nuts for the herbivorous animals (but no meat for the carnivores), and to sing "animal-rights carols" in protest against the National Zoo in particular and zoos in general.

"We are opposed to zoos," says Jenny Woods, a PETA spokesperson. "It's a pretty dismal life for the animals. Their cages are small. They're not in their natural habitats. The animals are what we consider imprisoned."

That view is hardly unusual. Indeed, it is nearly impossible to look at a majestic wild animal cooped up in a small cage and not wish to see it run free. Increasingly, zoo visitors question the morality of confining animals solely for the pleasure of gawking humans. And zoo employees sometimes feel the same way. "Zoos make me a little uncomfortable," says Dale Marcellini. "Some animals make me feel more uncomfortable in zoos than others. I think that's true of almost anybody. It makes me feel not very comfortable seeing a gorilla in a zoo, even though I work in a zoo."

In response to such sentiments, the National Zoo (and many others) has changed radically in the past 20 years, as curators and keepers have sought ways to give the animals more space and a richer life. Gorillas, for example, are no longer isolated in small, stark cages. Now, they live in social groups in large enclosures full of climbing structures and toys, and they are free to go outside and play in a grassy yard for several hours a day. "Once we learn that there is a better way," says Melanie Bond, "we like to think we're willing to change our philosophy."

But of course, such reforms only go so far: Zoos cannot -- or will not -- set the animals free or return them to the natural world.

Which doesn't bother zoo director Robinson. "The real world for the great majority of animals is incredibly stressful," he says. "It's a place of competition, predation, privation and social pressure of the most horrendous kind. Animals die of starvation. They're dismembered alive in great pain. The real world of so-called freedom is not a free one at all. It's a bloody mess out there. It's a battlefield."

Robinson -- a 61-year-old, British-born tropical biologist who spent two decades studying monkeys, spiders and crabs in Panama -- is a vigorous defender of zoos. They are essential, he says, to saving endangered species and to educating human beings about ecology. "I believe passionately that zoos are probably the most important force in informal education that we can muster," he says, "despite the opponents of zoos."

Robinson hopes to turn the National Zoo into a "Biopark" -- a place where animals, plants, fossils and human artworks are combined to reflect the interdependence of living things. "I'd love to build a glorious greenhouse full of hibiscus and orchids and all the marvelous flowers and then have butterflies and hummingbirds whipping around it," he says, all charged up at the idea. "And a model of an orchid that kids could crawl into and learn about pollination. Kids love to crawl in things. It's like going back into the womb."

Robinson bounds around the zoo like a wide-eyed kid, his anarchic reddish-blond mane bouncing off his head as he scoots along. He stops to say hello to a wolf he has befriended. He passes the kangaroos and says he hopes to build a walk-through exhibit with no barriers between kangaroos and visitors. He marvels at the newly installed shrubbery: "Oh, fantastic!" He picks up litter and deposits it in a trash can. He inspects the new pond, which will soon house Amazonian lilies so big they can hold a human. He spots a section of fence that's out of place, and he kneels down and ties it to a pole. He passes the camels and says he'd like to put an exhibit in the restrooms, comparing camel and human urine output. "Here's this thing four times larger than ourselves, and because it's got to conserve water, it produces far, far less urine . . ."

In the elephant house, he peeks in on the baby pygmy hippo, pets a pair of rhinos, then joins the crowd outside an elephant's cage. "There's nothing quite like looking an elephant in the eye," he says, beaming. "It's like that Melville obsession with Ahab and the eye of the white whale. You look at them and wonder: What's going on behind there?"

WHEN THE BIG BLUE TRUCK CAME TO TAKE NEKURU THE bongo to his new home in New Orleans, keeper Al Perry, 67, told the story of the day Nekuru was born. Perry walked up to the newborn to take his picture and Nekuru licked Perry's bald head. It was the start of a beautiful relationship.

"He loves to lick your face and suck on your shirt," said keeper Jeanne Minor.

Nekuru had passed all his blood tests, and the veterinarians had pronounced him fit to travel. Now, the keepers were using bales of hay to build a step so he could climb into the truck.

"Whoa! Whoa! Whoa! We're not gonna do it that way!" their boss, John Seidensticker, bellowed when he saw what they'd done. "We're not gonna do it just with hay. We're gonna get some mats under there. We go through this every god- dam time!"

Seidensticker picked up the bales of hay and stuffed some rubber matting under them. He fiddled with this makeshift staircase for a while, finally pronouncing it strong enough to support a bongo. Then, sweating in the hot sun, he helped the keepers lug sections of fencing for the construction of a secure walkway from the bongo's door to the back of the truck. When the truck driver started tying two sections of fence together with twine, Seidensticker shooed him away. "Wait for the ropes," he said. "I don't like twine."

Seidensticker was being careful. Very careful. He didn't want to become the goat in some soon-to-be-legendary bongo escape story. So he tied and retied the fences, then checked and rechecked the ties. Finally satisfied, he stationed Jeanne Minor at the back of the truck and revealed his game plan: "Okay, he's gonna be very scared and Al's gonna sort of nudge him, and as soon as he gets in, close the door."

When Nekuru's door swung open, the bongo stepped forward slowly and shuffled cautiously down the walkway, followed by Perry, who was holding a wooden shield.

"Go on, boy," Seidensticker said softly. "Go on."

Nekuru got to within a few steps of the truck, then he stopped and backed up a couple of steps, arching his back like a scared cat.

Seidensticker petted him through the fence. "Go on, boy, go ahead."

Nekuru paused a minute, then skipped into the truck. Minor closed the door behind him.

"You got him!" Seidensticker said, smiling for the first time all morning.

He signed some papers and handed them over to the driver. "If you run into any trouble," he said sardonically, "call New Orleans."

The truck driver climbed into the cab, started the engine, shifted into gear and eased slowly up the hill, carrying Nekuru toward a place far from the bird that dive-bombed the tiger; far from the artificial gorilla family and the keeper who is not yet fluent in gorilla; far from the giant panda that bit the hand that fed her and the raccoon that ate the $1,800 geese, and the orangutans that once enjoyed a picnic in the pansies; far from Robo-Badger and the black-footed ferrets and the pathological art collection; far from the herpetologist who studies zoo visitors, and the carol-singing zoo protesters, and the zoo director who wants to put a comparative urine exhibit in the restrooms; and far, alas, from Jeanne Minor, whose face he'd licked, whose shirt he'd sucked, and who was now watching the truck pull away and saying softly, "I'm gonna miss that bongo. He's a good guy."