To begin with, air lions were limited to the "northern" hemisphere of Uranus. Uranus is a topsy-turvey planet, tipped on its axis and rolling around the sun in the plane of its equator. The "northern" hemisphere, then, is that side of the planet which is always turned toward the sun--for which the sun is the pole star. This restriction on the area in which air lions may thrive imposed a natural limitation on the number of animals which there were in the first place. The demand for air lion pelts--despite the fact that the beasts were so large that an entire coat might be made from one of them--caused a dangerous depletion. * * * * * Nils's helmet broke atmosphere, and then hands were grappling him, helping him up the ladder, and pulling him aboard the "raft." The raft actually was a well constructed metal vessel; but, as it did not need a powerful engine, its motor was so weak that it hardly counted. Its gunwales rose only a few feet out of the air. Nils, as usual, fell to the deck with a clatter. One of the space-suited men on the raft knelt down to look at him. "Hi, Borgmann," the man said. "Congratulations." His name was Kerr. Nils smiled. Yes, it was worth congratulations. He was now only one lion--only one bonus--away from his goal, and then he could quit. And he'd be glad to quit. Dangling by a cable in liquid atmosphere is not safe work, and Borgmann was getting old for that kind of thing. Another man squatted down and said, "Yeah, Nils. Happy birthday." Birthday! Nils had forgotten all about it. That was right--he was thirty-five today. Realizing that he must have looked puzzled, he laughed. "It slipped my mind completely," he explained. "When you're on another planet, Earth dates get all mixed up." Kerr said, "The captain's ordered you aloft for a physical check-up. It came over the radio while you were down." Nils Borgmann stopped laughing. That could mean he'd never get a chance to make another plunge, never have another crack at an air lion, never collect that seventh bonus. They'd rotate him, put him on the mother ship and fill in on the raft with a substitute. Nils clambered to his feet, helped by Kerr and the other man, and walked over to take a look at the air lion he had just killed. It was a good, big beast, its fur still that faint yellowish color that was bleached out on Earth. It looked something like a walrus, but without any tusks. "Just one more," Nils said, "and I'm going to quit. I've got thirty thousand dollars in bonuses, on top of my pay." Kerr said, "That's almost enough to buy your wife an air lion coat. That'd be a nice present, so that you could be reminded of your happy days on Uranus every time she wore it." Nils laughed and said, "Go to hell." He was feeling pretty good again. Kerr always perked him up. After all, a physical examination might be just routine; they might find out that he could go on hunting air lions for five more years if he wanted to.