Night came and they slept above the stopping place of the ten Butrad ancients. And with morning they pushed upward through the soupy fog again. Abruptly the upward slanting slope ended. They looked out over a roughly oval bowl of slowly writhing mist and cloud. Dimly they saw the floor of the cavity. Several hundred acres of jungle-clad raggedness. Miniature buttes, mesas, and cliffs split the bowl into a hell of broken terrain, and here and there, near the black pocks of caverns in the rimming cliff walls, there showed little huddles of Butrad huts. "The Place of Birth," Masson said slowly. "All the tribes of the island must come here." Dolan nodded and rubbed the palm of his hand over the whetted edge of his hunting knife. "Plenty of guards stationed around the only entrances," he said, "just as you expected. I'll have to kill them off." Masson shook his head. "That would warn them. I may need weeks to learn the secret of their system of hatching the eggs." His webbed gray hand swept in a short arc. "Some of those caves must have other entrances. From the rim perhaps. That's what we'll look for." Dolan shrugged. "Right you are," he agreed. "My theory is," Masson said, "that Venus was formerly much warmer than it is now. For that reason the incubation temperature must be artificially raised. The question is: how much and how long must the eggs be artificially warmed. And do they use pools of all-but boiling water, or is the heat comparatively dry?" "That's for you to find out," said Dolan. "Me, I'm nothing but a truck driver. I ain't no college-brain guy." "You do all right," said Masson, grinning. "You seem to find your way around the jungle easy as a native." "Huh," snorted Dolan. "Ten years hammering the pavements and dodging traffic does that. You gotta have a quick eye and remember what you're doing." Masson got to his feet and moved back from the brink. "Let's start hunting," he suggested. * * * * * They crouched together in the dark shadows of the tunnel that opened a dozen feet above the floor of the large cavern. Down there, in the gray half-light that filtered in through the outer entrance, they saw three small heaps of vegetation steaming silently and the two old females who tended them. From time to time one of the old females filled a hollow husk from the nik-nik fruit with water and sprinkled it over the three mounds. The eggs they had seen the ancient ones bury so carefully were soaking up the moist warmth. Masson jogged Dolan's elbow, and they crawled carefully back along the low-roofed passage toward the vine-festooned entrance five hundred feet above. Water and gray ooze sloshed underfoot as they walked along level reaches of the way, and always the wet rock was slippery. "We know how the eggs are hatched now," he said, "and with experience we can learn to gauge the proper temperature. But until we have perfected the procedure our families will not increase very rapidly."