He turned the beam around, slightly. Again, there were sudden splashings. They died away. He turned the beam again. It was a nasty, snarling vibration in the water. So far as fish were concerned, it was more like a wall than a net, because not even the tiniest living creature could penetrate it. Not only fish fled before it. Shrimps and crabs and all types of crustaceans jerked and crawled and swam ahead of its motion. Jellyfish writhed when it touched them. Sea cucumbers contorted themselves. Everything that lived in the lagoon and could swim or crawl or writhe moved before the invisible barrier. Presently, the effect of crowding could be seen, and fish began to leap out of water. "This is a great advance in civilization," said Dr. Morton. "Men invented guns and destroyed the buffalo and the passenger pigeon! You may have made it possible to depopulate the sea!" Terry did not answer. The morning sun shone brightly, a gentle breeze made ripplings on the lagoon, the palms waved their fronds in languid gestures, and the surf could be heard booming and splashing on the outer reef. And about two dozen people stood on the wharf or on the _Esperance's_ deck and watched a spliced section of recorder-tape go through and through a recorder, which was set to make a sound underwater that could not be heard by the people above. The fish of the lagoon had crowded themselves into a minor embayment of the shore. There were innumerable leapings there. "There should be plenty of fish collected now," said Terry distastefully. "I certainly can't herd them ashore." The outboard boat pushed away from the yacht, its motor roaring. It reached the area in which the water seemed to seethe and surge with the motion of densely-crowded swimming creatures. The people in the boat examined the surrounding water, then the boat came back at top speed. "They're there!" called Davis. "And thick enough to walk on! I clearly saw some freaks that must come up from the bottom! We want to collect them!" "I speared five just now," Terry told him, "and one of them was wearing this." He held up the plastic object he'd found. There was silence for a moment. Then Dr. Morton said briskly, "We'll want fish spears. We'll take all the boats and go after some more of these piscatory oddities. Who's best with a spear?" Davis would go. He could use the two fish spears that were standard equipment for the outboard. The staff of the tracking station scattered to launch other boats. Only Terry and Deirdre remained on the _Esperance_. It was necessary for someone to stand by the recorder. Boats moved away across the water. One stout member of the island's staff trudged along the shore. "You're driving them," said Deirdre. "You are right." "I wish I weren't," said Terry. "Why?"