The future-man shook his head, sat down on the crude bench. "No one knows what happened to the Kralons after the Carboniferous Period," he said. "Nor does anyone understand why later insects retrogressed from the logical thinking of the Kralons' level of intellect, back to a mere set of complex instincts. "We do know that the Kralons made a mighty stride ahead of the rest of Earth life many millions of years ago. They've admitted to me that they have not progressed at all for untold ages now, and they're very worried. They don't know why they do not progress in an evolutionary sense as the rest of the life forms seem to be doing. "And they are exceedingly worried about the future, for we have let them know that apparently the Kralon race vanished around the end of the Carboniferous Period, leaving only diminutive descendants with instinct rather than intelligence to show that their race might ever have existed. "Of course, we of the future know that there is another similar parallel in the disappearance of the dinosaurs. As you probably have read in paleontological treatises, those huge reptiles seemed to have had everything their own way through the late Triassic, the Jurassic and the Cretaceous Periods." The engineer nodded. "I remember a paragraph from Gamow's 'Biography of the Earth' which I learned by heart," he said. "It went like this: 'The kingdom of giant reptiles, with its innumerable representatives on the land, in the sea, and in the air, was certainly the most powerful and most extensive animal kingdom during the entire existence of life on the Earth, but it also had a most tragic and unexpected end. During a comparatively short period toward the end of the Mesozoic era the tyrannosaurus, stegosaurus, ichthyosaurus, plesiosaurus, and all the other 'sauri' disappeared from the surface of the Earth as if wiped away by some giant storm, leaving the ground free for miniature mammals that had awaited this opportunity for more than 100 million years.'" * * * * * Malherne paused, reached in his jacket pocket and pulled out the half packet of cigarettes he had been hoarding. He offered them to Zor Ala, and when the other refused, he lit one and inhaled gratefully. "Then, in conclusion," Malherne continued, "Gamow says that the causes leading to the elimination of all the dinosaurs in a very short period of time are obscure. There are many hypotheses which have been advanced by various scientists to account for it. One theory was that the rising of general ground levels destroyed the inland seas and marshes. But that wouldn't have had any effect on the dinosaurs who had already fully adapted to dry land. Neither would it affect those reptiles who inhabited the oceans. So the whole episode has remained one vast mystery, without much chance of solution."