The sun-thrown shadows in the gap crawled steadily eastward. Knowlton tested the feed of his automatic, which, since its balkiness in the fight with the Peruvians, he had kept carefully oiled and free from the slightest speck of rust. Tim arose at intervals and paced up and down in sentry go, eyes and ears alert--a useless activity, but one which provided an outlet for his restless energy. McKay let his gaze rove over the small area visible from their post, studying the contours of the towering trunks, the prone giant whose fall had opened the hole in the leafy roof, the parasitical vines twined about other trees, the thin, outflung buttresses supporting the mighty columns--all familiar sights to him, but the only things to occupy his vision. So limned on his brain did the scene become that after a time he could close his eyes and see it in every important detail. It might have been two hours after Pedro and Lourenço had departed--the shadows had grown much longer--when over McKay stole the feeling that he was being watched. He glanced at his companions and found that neither of them was looking at him. Knowlton, sitting with hands clasped around updrawn knees, was dozing. Tim, though wide awake, was staring absently at a fungus. The captain's eyes searched the short vistas all about, spying nothing new. Still the feeling persisted. Then all at once his roaming gaze stopped, became fixed on a point some forty feet away. There rose a rough-barked red-brown tree, and from it, near the ground, projected a blackish bole. McKay was very sure the protuberance had not been there before. He had stared steadily at that tree more than once, and its shape was quite clear in his mind. Was that bump an insensate wood growth now revealed for the first time by the changing sun slant, or-- For minutes he watched it. It did not move. Then Tim, restless again, rose directly in McKay's line of sight, yawned silently, swung his gun to his shoulder, and began another slow parade of his self-appointed post. When he had stepped aside McKay looked again for the puzzling bole. It was gone. With a bound the captain was up and dashing toward the tree, drawing his pistol as he ran. But within three strides he went down. A tough vine, unnoticed on the ground, looped snakily around one ankle and threw him hard. His gun flew from his hand. As he fell a tiny whispering sound flitted past, followed by a small blow somewhere behind him. Ensued a gruff grunt from Tim and the swift clatter of a breech bolt. Raging, McKay kicked his foot loose and heaved himself up. Empty handed, he continued his rush for the tree. But when he reached it he found nothing behind it. If anything had been there it now was gone, and the vacant shadows beyond were as inscrutable as ever. Feet padded behind him and Tim and Knowlton halted on either side. A moment of silent searching, and Tim broke into reproach.