The B3 rocked slightly from time to time, but its descent was signaled more by changes in the light coming in through the portholes than by any sense of motion. The most drastic color change comes at the start of a dive. Red and yellow are wrung from the spectrum as if from a sponge. Green and blue dominate. Deeper still, the water color shifts to navy and finally becomes an intense black.

In the early stages of the dive, pilot fish, silver eels, motelike clouds of copepods, and strings of lacelike siphonophores drifted past the windows like tiny ghosts, along with shrimp, translucent squid, and snails so tiny that they resembled brown bubbles. Long, dark shapes could be glimpsed at the extreme range of the B3’s searchlight beam.

At seven hundred feet, Zavala switched the searchlight off. He looked out the window and murmured an appreciative exclamation in Spanish. Zavala had grown up in Santa Fe, and the view through the porthole looked like a New Mexico sky on a clear winter’s night. The darkness sparkled with stars, some alone, others in groups, some continuously flashing, others just once. There were floating threads of luminescence, and glowing smudges that could have been novas or nebulas in a celestial setting.

The cabin was as hushed as a cathedral; the loudest sound was the low hum of the air-circulation motor, so when Kane saw an undulating form float by the porthole his response was like a gunshot.

“Wow!” Kane exclaimed. “An Aurelia jellyfish.”

Zavala smiled at Kane’s excitement. Although there was no denying the beauty in the jellyfish’s undulating motion, the creature outside the bathysphere’s porthole was only a few inches across.

“Had me for a second there, Doc. Thought you’d seen the Loch Ness Monster,” Zavala said.

“This is so much better than Nessie. The medusae are among the most fascinating and complex animals on the face of the earth or under the sea. Look at that school of fish lit up like the Las Vegas Strip . . . lantern fish . . . Hey,” Kane said, “what was that?”

“You see a mermaid, Doc?” Zavala asked.

Kane pressed his face against the porthole. “I’m not sure what I saw,” he said, “but I know it was big.”

Zavala flicked on the searchlight, a green shaft of light edged with purple-blue stabbing the darkness, and he peered through the porthole.

“Gone,” he said, “whatever it was.”

“Beebe spotted a big fish he thought might have been a whale shark,” Kane said to the camera. “Until the bathysphere’s dive, his fellow scientists never believed that he had seen fish with glowing teeth and neon skin. He got the last laugh when he proved the abyss abounded with such strange creatures.”

“They’re getting stranger all the time,” Zavala said, pointing at himself. “The locals swimming around out there must think that you and I are pretty unsavory-looking additions to their neighborhood.”