Far to the right, a corps of centaurpede engineers had hauled up the huge tree trunk. Using it as a battering ram again, they smashed down a section of the barrier. Now they were rushing in, tearing the chargeless fence to pieces. As the two men watched tensely, another section collapsed with a splash into the mud. Instantly, the 'pedes began moving it toward the concrete wall. "I knew they'd find a way," said Swede. "They're going to use the fence segments as ladders." He turned away. Mac, continuing to stare down, suddenly stiffened. The 'pedes were acting queerly, moving around sluggishly, as if they had lost interest in their task! He frowned and faced his companions. "That's funny," he muttered. "They're stopping--they seem confused." Limpy shrugged and went on twirling the dials. Swede glanced out, then looked at Mac with upraised eyebrows. "They look the same to me," he said slowly. "You seeing things, Mac?" Startled, MacAloon shot his gaze back to the scene below. Swede was right! The 'pedes had resumed their work! Mac stood still for a moment, his mind racing swiftly, trying to grasp the significance of that momentary halt. Then he whirled, facing Limpy. "What were you doing just a moment ago?" Limpy raised his head from the dials. "Trying all the wave lengths. Adonis City isn't on its usual--" "I thought so!" Mac yelled triumphantly. "Get back to the length you had before!" "But there wasn't any answer." "They're halfway to the wall," Swede muttered abstractedly. "Get that wave length again!" Mac snapped. Limpy's right shoulder shrugged. He twisted the dial gently while MacAloon turned back to the window and stared out tensely. "Hold it!" he suddenly ordered. "Don't touch those dials!" Swede and Limpy looked at him puzzledly. He pointed down at the swarming enclosure. Limpy shuffled over to him, followed the direction of his finger. "They've dropped the fence," whispered the lookout. "They don't seem to know what they're doing." "Yah," Swede said in an awed voice. Below, the centaurpedes were moving about aimlessly, as if they had forgotten their orders. They had completely lost their terrible machine-like precision! "I don't get it," Swede complained in bewilderment. "What's wrong with them?" Mac's grin was hard and tight. "They're directed by a central brain, a sort of queen 'pede which coordinates their actions by ultra-short-wave commands, the way a queen bee directs a beehive. That's the secret of their synchronization!" "And I was working the ultra-short--" Limpy stopped, stunned. "That's the idea," Mac nodded. "Our signals blanket theirs! They can't get orders from the main intelligence, so they don't know what to do!" For a moment, the men were silent. Slowly, then, Swede said: "Now all we have to do is kill the brain." "Yeah," Limpy agreed bitterly. "What a chance of getting through! Where's the queen 'pede, or the brain, or whatever it is?"