It was the girl's voice that jerked them back to reality. "The other!" she gasped. "It's coming, behind!" They had completely forgotten the mass in the tunnel. Turning, they saw that it was only fifteen feet away and approaching fast, and instinctively they ran out into the cavern, skirting the sphere widely. When they came to Quade's wrecked borer Phil, who had snatched a glance behind, dragged them down behind it. For he had seen their pursuer abandon the chase and go to share in the meal of its fellow. "We'd best not get too far away," he whispered. "When they leave the front of the borer, maybe we can make a dash for it." For minutes that went like hours the young man watched, waiting for the creatures to be done, hoping that they would go away. Fortunately the sphere lay between, and he was not forced to see too much. Only one portion of one of the monsters was visible, lapping out from behind the machine.... At last his body tensed, and he gripped Sue and her father's arm in quick warning. The things were leaving the sphere. Or, rather, only one was. For Phil saw that they had agglutenated--merged into oneness--and now the monster that remained was the sum of the sizes of the original two. And more.... They all watched. And they all saw the amoeba stop, hesitate for a moment--and come straight for the wrecked borer behind which they were hidden. "Damn!" Phil whispered hoarsely. "It's still hungry--and it's after us!" David Guinness sighed wearily. "It's heavy and sluggish, now," he said, "so maybe if we run again.... Though I don't know how I can last any longer...." Holmes did not answer. His eyes were narrowed; he was casting about desperately for a plan. He hardly felt Sue's light touch on his arm as she whispered: "In case, Phil--in case.... This must be good-by...." But the young man turned to her with gleaming eyes. "Good-by, nothing!" he cried. "We've still got a card to play!" * * * * * She stared at him, wondering if he had cracked from the strain of what he had passed through. But his next words assured her he had not. "Go back, Sue," he said levelly. "Go far back. We'll win through this yet." She hesitated, then obeyed. She crept back from the wrecked borer, back into the dim rear, eyes on Phil and the sluggish mass that moved inexorably towards him. When she had gone fifteen or twenty yards she paused, and watched the two men anxiously. Phil was talking swiftly to Professor Guinness. His voice was low and level, and though she could not hear the words she could catch the tone of assurance that ran through them. She saw her father nod his head, and he seemed to make the gesture with vigor. "I will," she heard him say; and he slapped Phil on the back, adding: "But for God's sake, be careful!" And with these words the old man wormed inside Quade's wrecked borer and was gone from the girl's sight.