tile reared up and made a movement toward
them. Marable and the girl retreated swiftly, as the beast thumped to
the floor with a thud and started at them, advancing with a queer,
crawling movement.

It was between them and the door. Betty thrust her gun into Marable's
hands, for his own was empty and he had hurled it at the monster.

"Hurry! Run for your life!" ordered Marable, placing himself between
Betty and the reptile.

She would not leave him till he swerved to one side, going dangerously
close to the beast and firing into its head. The rush of the flowing
body stopped; it turned and pursued him, leaving the girl safe for the
moment, but separated from Marable.

Luckily, on the smooth marble it could not get an efficient grip with
its clawlike arms. It was clumsy in its gait, and for a time the man
eluded it.

Betty Young, looking about for a weapon, calling for help at the top of
her lungs, caught sight of a fireman's ax in a glass case on the wall.
She ran over, smashed the glass with the small hammer, and took out the
heavy ax.

Shot after shot reverberated through the big laboratory as Marable tried
to stop the monster. Betty, bravely closing in from the rear, saw
Marable leaping from side to side as the brute struck viciously at him
time and again.

The creature had been emitting cloud after cloud of black fog, and the
atmosphere, in spite of the open windows, was dim in its vicinity.
Vaguely Betty heard shouts from the far hall, but all she could do was
to call out in return and run toward the horror.

* * * * *

Marable, out of breath, had climbed to the top of an amber block. Betty,
close by, saw the reptile rear its bulk up into the air, until it was
high enough to strike the man.

Before it could send forth its death-dealing fang to pin Marable to the
block, however, Betty Young brought the ax down on its back with all her
strength.

There was a sickening thud as the sharp weapon sunk deep into the fleshy
back. She struck again, and the creature fell in folds, like a
collapsing spring. It lashed back at her, but she leaped clear as it
slashed in agony, thrashing about so that the whole room seemed to rock.

Marable came scrambling down the side of the block to help her. He was
breathing hard, and she turned toward him; as Betty looked away, a
portion of the scarlet tail hit her in the body and she fell, striking
her head on the floor.

Marable reached down