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.

John McCarthy was climbing into the opening behind the other men, when
he happened to glance back. His flashlight dimly lighted the spot where
the monster had been, and _it was gone_!

He hesitated with one foot in the air, then realized what had happened.
The movement of the body had moved it farther and farther from the
center of the dome. It had reached a place where the curve was
sufficient to let it slide on the smooth metal. A