Several times footprints, large-booted but short-paced, led the Daytons on, only to be lost in rocky ground and lichen. Twice Joe and Doran crossed the war-fused wrecks of huge cities. Fallen hothouse roofs littered the ruins. The piles of rust must have been irrigation pumps, spaceship ramps, climate-controlled apparatus. In tower, storehouse, and avenue were the skeletons, with their odd, vertical ribs to house huge lungs. Some devices still worked. Joe found a rod, probably of corrosion-resistant platinum. He pressed its stud and for an instant, before it became useless, it flashed fire that melted part of a fanciful wall-carving. The struggle to survive harshened further. Once it was bitter water, oozing up from some deep irrigation pipe, that staved off death by thirst. Several times oxygen was obtained only by lying prone over a teeming colony of the chitinous creatures whose instinct was to roof with a protecting airdome of gluten, anything that promised to be food. These Mars ants--ordinarily to be avoided--admitted air to the domes they built from their deepest buried tunnels and chambers. * * * * * Often Joe looked at his wife, knowing that they both had changed. They were tattered, and a little like the bas-relief figures. They were Dave Kort, and Frank and Will Terry over again. Doran's teeth were very white in a face browned by sunshine filtered only by the rare Martian air. She was very thin, but there was an oblique charm in her features. Or had his very conceptions of beauty altered subtly, conforming to a now familiar environment? Thinking back to Port Laribee and Earth itself was often like recalling substanceless dreams, so different were such memories. And was the fading of revulsion for even the scurrying builders of the air-domes occasion for deeper fear because it represented the loss of another part of one's natural self? Joe often worried. Others had been drawn to Mars too, eager to search out the mysteries of its past and people--all of this an intriguing fabric--but most Earthmen had the sense to realize in time that it was a graveyard world, unfit for humans. For to live the life of Mars you had to stop being human. Conditioning grimed into you like the red dust. Nor was the trap just imaginary. The most frightening part was knowing that Doran was with child. Damn the pulse-beats of life that had no regard for circumstances! Joe could be glad only that she remained human enough to be pettish and optimistic by turns. "We can't get back, can we, Joe?" she'd say. "But maybe it'll be all right. It's a long time, yet." Should they try to hole up, somewhere? That wasn't much good, either. Even in spring there wouldn't be enough resources in one place to sustain life for long. They had to keep moving. So when again they saw those boot-tracks, they felt free to follow.