The end of the tank distant from Harris was opaque. He thought that there were connections to a towing vehicle as well as to the plant that pumped air for him. The big fish had not made that quite clear to him. All other sides of the tank were quite clear. Whenever he walked about, he could look through the floor and find groups of shells and other remnants of deceased marine life in the white sand. Occasionally, he considered the pressure that would implode upon him should anything happen to rupture the walls, but he had become habitually successful in forcing that idea to the back of his mind. Along each of the side walls were four little airlocks. The use of these was at the moment being demonstrated by one of the sea-people to what Harris was beginning to think of as a child. The parent was slightly smaller than Harris, who stood five-feet-five and weighed a hundred and thirty pounds Terran. It also had four limbs, but that was about the last point they had in common. The Tridentian's limbs all joined his armored body near the head. Two of them ended in powerful pincers; the others forked into several delicate tentacles. The body was somewhat flexible despite the weight of rugged shell segments, and tapered to a spread tail upon which the crustacean balanced himself easily. Harris felt at a distinct disadvantage in the vision department: each of the Tridentians had four eyes protruding from his chitinous head. The adult had grown one pair of eye-stalks to a length of nearly a foot. The second pair, like both of the youngster's, extended only a few inches. The Terran could not be sure whether the undersea currency consisted of metal or shell, but the Tridentian deposited some sort of coin in a slot machine outside one of the little airlocks. It caused a grinding noise. Directly afterward, a small lump of compressed fish, boned, was ejected from an opening on the inside. "Goddam' blue lobsters!" swore Harris. "Think they're doing me a favor!" He let them wait a good five minutes before he decided that the prudent course was to accept the offering. Sneering, he walked over and picked up the food. There was usually little else provided. On days he had been too angry or too disgusted to accept the favors of sightseers, his keepers assumed that he was not hungry. In the beginning, he had also had a most difficult time getting through to them his need for fresh water. That was when he had come to believe in the large, fish-like swimmer who had transmitted his thoughts to the sea-people. The fact that the latter could and did produce fresh water for him aroused his grudging respect, even though the taste was nothing to take lightly. He juggled the lump of fish in one hand, causing the little Tridentian to twirl his eye-stalks in glee and swim up off the ocean bottom to look down through the top of the tank. The parent also wiggled his eye-stalks, more sedately. Harris suspected them of laughing, and turned his back.