A thud came, that didn't vibrate quite as much, and the men could feel the hair on their necks stiffen. It was now or never, and Dick fired although he was still several feet from the opening. He fired at the topmost section of the ram, hoping it might stop the hammering for a moment even if it didn't injure the equipment. Two more shots rang out, before the object could deliver another blow. _It was alive!_ The heavy ram _jumped_ from the shock of the bullets, curving convulsively to one side of the opening. Then it drew back out of sight. CHAPTER VIII _Battle with a Monster_ Minutes passed, while the earthmen hardly dared breathe. Their ebbing heartbeat seemed to almost echo in their breasts. Then the object appeared at the opening, hesitated, and was thrust in! _The hammer was a head!!!_ It swayed back and forth, like the head of a huge caterpillar, and every gun fired in unison. Shot after shot pumped into the head with rapid and unerring accuracy. The giant head moved from one side to the other, while two gigantic eyes peered around. It didn't know enough to draw back from the danger zone, but muscular reaction finally moved it out of sight. Dick crept forward, motioning for the others to wait until he investigated. There was no need for all of them to enter the danger zone. He turned the flashlight on, that had been strapped to his waist, and played it around the jagged opening, then climbed to the next level and searched again. When he crawled to the outer surface, the creature was writhing a few feet away. He motioned, and the other men soon joined him, where they could watch the creature. They were standing almost on the direct center of the dome, where it was almost flat. The flashlights penetrated the mists enough to mark out the shape of the attacker, when they were all centered. Suddenly they felt sick to their stomachs. It _was_ a caterpillar! As loathsome a creature as they could have imagined with its curled body, and the farthest possible thing from a human being. A form of life that existed in the poison gases, where men would die within minutes. The muscles of the creature had to be terrifically strong, to move against the gravity of the huge globe. Even at the center of the dome, they felt less effect of the neutralized gravity of the interior. It required effort to stand on their feet. Some effect of the neutralizers in the giant pillars, which eliminated most of the weight of the dome, enabled them to handle their bodies. The creature before them was accustomed to normal gravity of the heavy planet, and even the metal of the dome was not beyond the pounding of its hammer. What they had mistaken for a battering ram, was the brown tip of the mammoth insect. From end to end it measured over sixty feet. The men finally turned away in disgust, as it writhed in muscular reaction.