It took form slowly, a shapeless, round blur in the pale light. Inch by inch it drifted toward them, until Chet moved one hand abruptly and found he had created a ripple of light by which he could see more clearly. And he saw before him a bulging, membraneous sac. It had been smoothly spherical before; it heaved itself into strange protuberances as he watched. He flipped his hand to set up another vortex of light, and he saw the first rip that formed in the membrane. Before his staring eyes the bag burst open; and Chet, who had wished for some substantial thing, even a denizen of this wild world, found his wish fulfilled. For the thin membrane tore in a score of places to release a body from within--a shapeless, huddled mass of chalk-white flesh in a wrapping of black leather that unfolded before his eyes and became wings which waved feebly in their first attempt at flight. The pallid body, supple as a giant worm, jerked spasmodically and turned sightless eyes toward the watching Earth-folk. Then, as if drawn by some magnet, invisible in the distance, the black wings began to beat the air, and the creature moved off in a straight line toward some unknown goal. * * * * * Another of the membraneous spheres drifted past in the light that came from those fluttering wings. A second showed in repulsive shininess. Chet was aware that there were many of the things about. "Eggs!" he exclaimed with a disgust that partook of nausea, "And the damnable thing hatched--right here!--before our eyes!" And the girl gave the final explanation: "The Moon is just a great shell. They lay their eggs, these half-human creatures that you saw, and attach them to the inner surface of that shell. Then at a certain period they come loose and float away. I never knew what became of them; now I understand at last." "You know all this!" protested Chet. "How can you know it? How long have you been here?" "I kept track of time for a while," said the voice beside him; "then I forgot it when they took Frithjof away. But it must be about five years. Five years of terror and vain hopes and wild plans for escape! And now it ends--after five years!" And Chet Bullard, within his metal helmet, was repeating in bewilderment: "Five years! Haldgren left five years ago! What does it mean?" Nor did he pause to realize that through his amazement was woven a thread of another hue, tinged faintly with jealousy that demanded of him: "Frithjof! Who is Frithjof who was taken away?" Chet's mind was filled with a confusion of questions that jostled one another to silence when he tried to give them expression. And there was little time for questioning. * * * * *