Today's traveler can find more lushly tropical islands, but -- as the young Charles Darwin learned -- few will prove as rewarding as the Gala'pagos, which rise in stark volcanic splendor from the Pacific Ocean 500 miles off the coast of Ecuador.

Darwin made his mind-altering visit to the Gala'pagos Islands 150 years ago this fall aboard the survey ship Beagle, which was stopping at some of the world's most remote areas on a globe-encircling trip of more than four years. With this anniversary in mind, 14 of us recently sailed around the steep and rugged islands, anchoring offshore and beaching small boats for our own overland explorations.

We found the 10 main islands and smaller outcroppings to be much as Darwin described: diverse, and each with its own peculiar animal and plant species.

One island was a world of moonlike craters. Another had a vast lava flow that looked like a black hell.

Yet others abounded in playful sea lions and courting albatrosses. And we saw the unique giant tortoise, or land turtle ("galapago" is Spanish for land turtle), and walked among the big lizards called iguanas.

We didn't see any humans on most of our explorations. In fact, there are only several thousand inhabitants -- mainly farmers and fishermen -- living primarily in a village near the Darwin Laboratories on Santa Cruz. But the Gala'pagos Islands, rich in exotic reptiles and birds, fascinated us as they have sailors and scientists for centuries.

By the 19th century, 50 or 60 whaling ships stopped there each year and captured thousands of the islands' unique 500-pound tortoises. (So plentiful were the tortoises and the three-foot-long iguanas that in "Moby Dick," Herman Melville wrote that "the chief sound" of the islands "is a hiss.")

We were able to approach these giant reptiles and pet their heads and necks. Darwin found the tortoises so hard of hearing that he could approach from behind and climb aboard for a ride.

One afternoon, we waded ashore to a primitive "post office" started when outbound whaling ships left mail in a box there for returning ships to pick up and deliver back home. A post card I addressed to my wife and left unstamped in this same untended box arrived three weeks later. It had been carried to the United States by another visitor and then mailed.

Our small group -- graduate biology students and adventurous travelers -- had been brought together by biology writer and professor Charles V. Covell of the University of Louisville. We traveled eight days around the islands on the commercial yacht Isabela. It is the smallest of the ships regularly carrying visitors through these waters and was ideal for our group. (The largest ships, the Santa Cruz and the Buccaneer, each carry 90.) Our flight from Miami, a short stop in Quito, the Ecuadorean capital, and the trip on the Isabela were arranged by Holbrook Travel Inc. of Gainesville, Fla., which specializes in scientific and educational tours of the Gala'pagos.

The ship's cook fed us well: papaya chunks, blueberry juice and banana pancakes for a typical breakfast, and avocado soup, fresh-caught grouper and lobster among the fare for lunch and dinner.

Darwin, we read, ate tortoise and iguana, but that day has passed. We carried an official naturalist, Eduardo Carriozo, whose job was to make sure we made no change in the environment, carrying not even a shell away from this Ecuadorean national preserve. But that was only part of his work. Each evening after dinner, he showed slides of what we might see "if we are lucky" the next day.

And we were lucky, thanks to his observing eyes. We even saw whales spouting as we sailed between islands. We spotted sea turtles in the ocean, too. And the happy dolphin became so commonplace we stopped running for our cameras.

Often, we took the Isabela's small boats to explore the cliffs along the shores. Birds swirled overhead and nested in the rocks. Many of them, like the tropic bird with its long, skinny tail, were entirely new to me.

It was Eduardo who first saw three penguins at the bottom of a cliff. (These were a smaller, darker type than found in colder areas.) One of the penguins strolled off, leaving the other two in privacy. Later, while snorkeling, I saw a pair of penguins plunge through the water ahead of me, diving for their dinner. They swam using their webbed feet and flipperlike wings for propulsion, looking like birds "flying" through the water -- which is the closest penguins get to true flight.

Most days about half of us snorkeled, sometimes from the Isabela, but usually from an island's beach or rocks. The water was cold as a result of the polar current, which also kept the islands from getting anywhere near as hot as we had expected.

We found coral areas to explore, and we saw a rich variety of fish, many brightly colored. Once, my view was obscured by a school of fish so numerous and dense I could see nothing else. One day, skates glided silently along the sea's floor 25 feet below. Another day, we saw moray eels in the shoreline rocks.

We had friendly companions, too: sea lions. Big, friendly companions, they are, and they like to swim with visitors. Finding one close by on either side, and a third flipping along below, can make you bite hard on your mouthpiece!

Still, they seemed so human, sprawling on their backs with their fat bellies toward the sun, or dozing on their sides or stomachs along the beaches or on the rocks. Unless they had a cub, they took little notice as we came by.

On some islands, the birds were thick as pigeons in a city park, but much odder and more spectacular:

There was the flightless cormorant, which uses its truncated wings to swim after its supper. This type of cormorant lives nowhere else in the world but on two of these islands. And there were albatrosses, boobies and frigates -- all bigger and more exotic than the birds back home.

For these and other birds, the islands are safe nesting areas. They seemed to expect no harm and, even when nesting with their young, paid little attention as we strolled by, taking close-up photographs.

"Isabelans!" our ship's naturalist cried one morning. "We are in luck! The albatrosses are courting!"

Two of the huge white birds -- their wingspans sometimes reach 11 feet -- sat facing each other, each making a sharp, clicking sound by snapping its own five-inch beak open and shut. Then they clicked cooperatively, the male and female each striking its bill against the other's. Having clicked, they threw their heads up, opening their beaks as if making a soundless cry of ecstasy. What a ritual it seemed -- and the stranger still when we were told they will not mate for another year.

The boobies' courtship was quicker. The male whistled. The female squawked back, but apparently didn't mean it. Nearby we saw other boobies' nests with fluffy white chicks.

Most boobies are comical-looking, with big, wide-apart eyes and awkward, bright red or bright blue webbed feet. (The red-footed ones are the only birds in the world with webbed feet that can grasp a limb or a rope and perch on it. This keeps them out of conflict with the blue-footed type, which nests on the ground.) There is also an elegant booby, if you can believe it: the masked booby, a whiter-than-white creation with eyes ringed in black.

The great frigate bird is a blackbird, in the way the SST is a flying machine. We often saw this huge, beautiful bird glide and soar on its gracefully bent wings -- and then swoop to snatch food from other birds, or even twigs for nesting. On a cliff high above the ocean, we held twigs overhead and the frigates, gliding from out of the sun at great speed, snatched them from us, too.

With beauty, size and the name "great" going for it, the male great frigate can get puffed up. We saw him blow up the red wattle on his neck (similar to a turkey's, but brighter) into an astounding red balloon, almost doubling his body size.

On island after island, we also spotted different kinds of finch. Unlike most of the islands' birds, these are small, dull things you might think no more about than an English sparrow -- but they were of phenomenal importance to Darwin in eventually forming his theory of evolution by natural selection.

Each day, we returned to our boat to sprawl about the fantail, nurse an excellent Ecuadorean seltzer, a beer or martini (the Isabela boasts a bartender and hors d'oeuvres) and talk about what we had seen. Frequently, we also shared the observations of Charles Darwin, whose "Voyage of the Beagle" is as chatty a read as his more formal books are ponderous.

Thus, after spotting various species of finch, we shared Darwin's puzzlement that there would be so many different kinds of the little bird from island to island -- alike in most ways, but with big beaks on an island where there were seeds to be cracked or, on another island, with bills suitable for subsisting on the fruits and flowers.

There is no woodpecker on the islands to probe for grubs, but Darwin observed a unique species of finch in the woodpecker's environmental niche, using a cactus spine held in its beak to extract insects.

We read Darwin's journal as he described, with typical modesty, how it hadn't occurred to him that each island might have its own unique species until he heard the vice governor of the islands remark that he could always tell which island a tortoise came from because the shells differed from place to place. After that, Darwin said, he kept his species collections separate, island by island.

Darwin found many similar examples during his stay of a little longer than a month. These species of plants and animals unique to each island amazed him -- living, as he was, in a time when scientists believed all species were unchanging and unchangeable. He counted 30 plant species unique to James Island, 26 unique to Albemarle and 29 unique to Charles.

The species Darwin saw and collected on the Gala'pagos were to occupy his thoughts for many years before he developed an explanation for them. But Darwin was far quicker to see the other benefits of his voyage.

On our last night out, I read Darwin's view that others "cannot expect to be as fortunate in their companions as I have been," but that "I have too deeply enjoyed the voyage" not to recommend such trips to others. The trip, he made clear, had stretched his young views. And, moreover, it had been an adventure. It had been great fun.

I thought back on what we had seen, on our good-humored ceremonies as we crossed the equator, on our naturalist smiling through a bout of seasickness, on our eye-opening treks across the islands and our wet landings on the beaches.

"Amen, Charles Darwin!" I said. "Amen!"