He moved silently toward the foot of the cliff up which Tarzan could presently see him ascending like a great fly on a wall. In the dim light the ape-man could not see the pegs set in the face of the cliff. Om-at moved warily. In the lower tier of caves there should be a sentry. His knowledge of his people and their customs told him, however, that in all probability the sentry was asleep. In this he was not mistaken, yet he did not in any way abate his wariness. Smoothly and swiftly he ascended toward the cave of Pan-at-lee while from below Tarzan and Ta-den watched him. "How does he do it?" asked Tarzan. "I can see no foothold upon that vertical surface and yet he appears to be climbing with the utmost ease." Ta-den explained the stairway of pegs. "You could ascend easily," he said, "although a tail would be of great assistance." They watched until Om-at was about to enter the cave of Pan-at-lee without seeing any indication that he had been observed and then, simultaneously, both saw a head appear in the mouth of one of the lower caves. It was quickly evident that its owner had discovered Om-at for immediately he started upward in pursuit. Without a word Tarzan and Ta-den sprang forward toward the foot of the cliff. The pithecanthropus was the first to reach it and the ape-man saw him spring upward for a handhold on the lowest peg above him. Now Tarzan saw other pegs roughly paralleling each other in zigzag rows up the cliff face. He sprang and caught one of these, pulled himself upward by one hand until he could reach a second with his other hand; and when he had ascended far enough to use his feet, discovered that he could make rapid progress. Ta-den was outstripping him, however, for these precarious ladders were no novelty to him and, further, he had an advantage in possessing a tail. Nevertheless, the ape-man gave a good account of himself, being presently urged to redoubled efforts by the fact that the Waz-don above Ta-den glanced down and discovered his pursuers just before the Ho-don overtook him. Instantly a wild cry shattered the silence of the gorge--a cry that was immediately answered by hundreds of savage throats as warrior after warrior emerged from the entrance to his cave.