The air is crowded with jungle vines and alive with jungle screeches. Tapirs live here, together with creeping Komodo dragons, surreal hornbills, even insects and mice. The toothy crocodilians, half submerged, can be seen from under water level. Close overhead swing the gibbons and proboscis monkeys. Only the black leopards and certain snakes are segregated from visitors by protective glass. Otherwise, it's just you and them: sharing the same air, deep in the jungle.

For its newest and most enchanting habitat -- the unique Jungle World that's opening June 22 -- the Bronx Zoo has spared little in time, effort, expertise and millions. A volcanic island ravine, a coastal mangrove swamp and a vast Southeast Asia rain forest have been re-created to the last convincing detail inside a labyrinthine, walk-through building. It is sky-lit and cloud filled, with pools, streams and waterfalls, bamboo and ferns.

Some of the Jungle World's banyan trees are models -- man-made replicas. But the trees outside are the real thing, a real northern forest: The zoo was begun in 1899 (it's one of America's oldest), sited on 264 acres of what the zoo terms "virgin woodland." The Bronx itself has changed a lot, but the zoo remains innocent of logging or forest fires, so now when children and grown-ups come to view the 3,600 wild animals, they do so in the shade and company of thick oaks and towering tulips -- unusually grand and mature trees for an urban setting.

The Bronx is not the only part of the world beyond the zoo that's changed. The natural environments of many wild animals have been cultivated, exploited and polluted out of existence. Accordingly, the job and the character of zoos is changing: Early in this century, single sample animals were brought in out of the buzzing, blooming confusion of a wild world to be -- literally -- showcased for a "civilized" audience. No more. Now, the Bronx Zoo has fewer species, but more animals; instead of showing caged samples, it is stockpiling herds. More and more, the zoos' job is to ensure a future for wild animals after the wild is gone.

As the animals' wild habitats get obliterated in the outside world, the zoo is creating "wild" habitats inside the zoo. The Bronx Zoo was a pioneer in creating habitats: In 1941, it opened its five-acre outdoor African Plain where lions were separated from antelope and zebra -- and onlooker -- by a dry moat.

Ever since, the Bronx Zoo has been preserving its woods and creating "natural" environments. It is phasing out the cells for the large animals, in favor of open habitats that allow them to move freely in something akin to natural surroundings -- and to be observed by visitors in a more direct and satisfying way.

One landmark event was the 1977 opening of the zoo's version of Wild Asia: On 40 acres of forest and meadow along both sides of the Bronx River, about 200 mammals and birds rove, feed, snooze and strut. Antelope, rare sika deer, gaur, lesser pandas and peafowl share this habitat (as they would in wild parts of Asia) with elephants, Indian rhinos and tigers. From May through October, all can be observed from above from a two-mile monorail train, the Bengali Express.

Other open habitats have followed: a three-acre veldt shared by giraffes, ostriches and a herd of rare Grevy's zebras. Nearby, a pair of cheetahs have the run of a hilly, open area. There's a range that's home to a herd of American bison -- an animal the zoo was instrumental in saving after it had been hunted to near-extinction. The six-acre Rare Animal Range now ensures the survival of orphan herds of yak, Mongolian wild horses and the wonderfully antlered Pere David's deer, which are the animal photographer's favorite (they hold still even when they're awake). Another open area will accommodate the zoo's burgeoning family of rare Himalayan snow leopards.

Under the zoo's trees are high, airy habitats for bird groups, and low, wet habitats for waterfowl and otters. The raucous, snorting sea lions enjoy their own replicated piece of the rocky California coast -- where the dominant blowhard is a whiskered veteran named Moose.

There is far more here than can be seen in a day: the hands-on Children's Zoo, the Wallace World of Birds (a free-flight aviary), a World of Darkness featuring hyperkinetic bush babies, the Reptile House with its nursery for young reptiles, the North American Trail among the great bears and shy wolves. And more.

When immobilized by zoo foot (a variant of museum foot), you can ride: an aerial tramway, a llama or pony (if you're child-size), a camel or even an elephant. Or you can stop and watch: One of the zoo's most popular shows has not changed. The lions and tigers dine daily at 3:30.