By the time humanity traveled to the stars, medical biology had made it possible to regenerate damaged or deficient organs of the body. Regeneration was limited only by advanced age. Sometime after a man's two hundredth year his body lost the ability to be coaxed into growing new cells. A fifth set of teeth was usually one's last. As long as senescence could be staved off, however, any man could have bulging biceps and a pencil waist, if he could pay for the treatment. Until the medical associations declared such treatments unethical there was even a short fad of deliberate deformities, with horns at the temples particularly popular. From regeneration it was a short step to specialized regrowth. The techniques were perfected to adapt humans to the dozen barely habitable worlds man had discovered. Even on Mars, the only planet outside Earth in the solar system where the human anatomy was remotely suitable, a man could work more efficiently with redesigned lungs and temperature controls than he could inside a pressure suit. On more bizarre planets a few light-years away the advantages of changeling bodies were greater. Unfortunately for planetary development companies, hardly anyone wanted to become a changeling. High pay lured few. So a law was passed permitting a convicted criminal to earn his freedom by putting in one year as a changeling for every five years he would otherwise have had to spend in rehabilitation. "What types of changelings do you have orders for right now, doctor?" Asa asked the man assigned to his case. It would look suspicious if he asked for Jordan's Planet without some preliminary questions. "Four," answered the doctor. "Squiffs for New Arcady. Adapted for climbing the skycraper trees and with the arm structure modified into pseudo-wings or gliding. Then we need spiderinos for Von Neumann Two. If you want the nearest thing we have to Earth, there's Caesar's Moon, where we'd just have to double your tolerance for carbon monoxide and make you a bigger and better gorilla than the natives. Last, of course, there's always a need for muck men on Jordan's Planet." The doctor shrugged, as if naturally no one could be expected to choose Jordan's Planet. Asa frowned in apparent consideration of the alternatives. "What's the pay range?" he asked. "Ten dollars a day on Caesar's Moon. Fifteen on New Arcady or Von Neumann Two. Twenty-five on Jordan's." Asa raised his eyebrows. "Why such a difference? Everyone knows about muck men living in the mud while they hunt Slider eggs. But don't your conversions make the changeling comfortable in his new environment?" "Sure they do," said the doctor. "We can make you think mud feels better than chinchilla fur and we can have you jumping like a grasshopper despite the double gravity. But we can't make you like the sight of yourself. And we can't guarantee that a Slider won't kill you." "Still," Asa mused aloud, "it would mean a nice bankroll waiting at the end of the year."