e great nursery,
just stood where it was and sliced the air rhythmically with its jaws.

"We haven't a chance of walking through _that_ exit!" Dennis agreed.
"Let's try the other side."

* * * * *

But before they could half cross the great room--walking between rows of
life that weakly stirred like protoplasmic mud on either side of
them--a soldier appeared at that door, too. Like the first, it stationed
itself there, and began the same regular, swift slicing movements of
jaws that compassed the doorway from side to side and halfway from top
to bottom.

"We might possibly be able to run through that giant's nut-cracker
before it smashed shut on us," said Jim dubiously. "But I'd hate to try
it. There's a door at the end, too."

They made for this, running now. But a third soldier appeared to block
the way out with those deadly, clashing mandibles.

"You're _sure_ they can't see?" demanded Jim, clutching his spear while
he hesitated whether to try an attack on the fearful guard or to turn
tail again. "Because they certainly act as if they did!"

"Direct commands from the ruling brain," Denny surmised soberly.
"Somewhere, perhaps half a mile down in the earth, Something is able to
see us through solid walls, read in our minds our intentions of what
we're to do next, and send out wordless commands to these soldiers to
execute countermoves."

"Rot!" said Jim testily. "These things are bugs, not supermen. And the
fact that they're now bigger than we are, and much better armed, doesn't
keep them from being just bugs. There's no real brain-power in evidence
here."

But an instant later he changed his mind. They approached the fourth and
last exit from the giant chamber. And here there was no guard. They were
able to race out of it without interference. The oddity of that was
glaring.

"Denny," gasped Jim, "we're being _herded_! Driven in a certain
direction, and for a certain reason, by these damned things! Do you
realize that?"

Dennis did realize it. And a moment later, when he glanced behind, he
realized it more.

* * * * *

Behind them, marching in orderly twos that filled the tunnel from side
to side, moved a body of the soldiers. As the men moved, they moved;
never coming nearer and never dropping behind.

Experimentally, Dennis stopped. The grim soldiers stopped, too. Dennis
walked back toward them a step or two, spear held ready.

The mo