The big Jovian, they learned, was chief of the ship. He told them his name was Musters, and introduced his officers. They were an intelligent, efficient lot. From them the Earthmen learned something of the social organization of the human race as it survived on Jupiter. "The race followed its natural evolution," intelligent and handsome young Lieutenant Reko explained to Sine as they leaned against a railing and gazed out of an unshuttered port at the somber splendors of Jupiter as it gradually swelled and covered the firmament. "Like mated to like, and so the superior individuals became more superior, and the inferior ones more inferior. This resulted eventually in two races. Naturally we took steps to properly segregate the inferior race. Our efficiency experts have found ways to put them to work--to make them quite useful in fact. Of course we could not trust them with our weapons, our ships, our really important central power plants----" What were these inferior--these so-called _Mugs_--what were they like? Reko arched aristocratic eyebrows. Why, they were often quite human in their appearance--though occupational diseases, and so forth----. Sine gained the impression that they were kept out of the way in order not to disturb the esthetic comfort of the superior race. "There was a time when we had trouble with them," Lieutenant Reko said. "There were trouble makers among them. They attacked the homes of the First race, seized power control stations. Not fifty years ago there was an insurrection. But the Mugs lost. Thousands upon thousands of them were driven into the swamps and caves on the edge of the Tenebrian Sea. They were never seen again, although we searched for them with our heat rays. Perished, no doubt." None were left now, Reko said, except those actually and fully occupied at certain labors for which they were found efficient. They were allowed to reproduce in sufficient numbers to fill the requirements--no more. "What a rotten fate!" Sine exclaimed. "They are quite a terrible people," Reko pointed out, closing a distasteful subject. A few sleep periods later Musters called his terrestrial guests to his cabin. "I have a pleasant surprise for you," he told them in his musical baritone. "Our planetary conference would wish for me to give you a most pleasant impression of Jupiter, so that interplanetary relations may be resumed under the best possible conditions. For that reason I am going to land you on a satellite that I'll wager will be a revelation to you. It is the goal and object of every one of our people. But it is costly and only a small portion of our population can be accommodated at a time. You may judge the kind of place it is by the name the public has given it: 'The Pleasure Bubble.' Come to the astrogator's cabin now; I'll show it to you." They followed Musters to a compartment in the rounded bow of the great ship, stared out of a quartz port between opened shutters.