when the monster comes along, I am pretty sure that you will be able to see it. You may see a little more as your eyes get accustomed to it."
"I can see very dimly," announced the lieutenant in a moment.
Dimly the walls of the cave and the platform before them began to take vague shape. The three stared intently down the beam of ultra-violet light which the doctor directed down the passageway leading deeper into the cave.
"Good Lord!" ejaculated Carnes suddenly.
Slowly into the field of vision came the hideous figure they had seen on the film. As it moved forward a rustling, slithering sound could be heard, even over the bellowing of the steer and the hum of the apparatus. The odor of musk became evident.
Along the floor toward them the thing slid. Presently it reared up on its hind legs and its enormous bulk became evident. It turned somewhat sideways and the correctness of Dr. Bird's hypothesis as to its peculiar shape was proved. All of the bulk of the creature was in two dimensions. Forward it moved, and the horrible human hands stretched forward, while the mouth split in a wide, toothless grin. Nearer the doomed steer the creature approached, and then the reaching hands closed on the animal.
There was a blinding flash, and the monster was hurled backward as though struck by a thunderbolt, while a horrible smell of musk and burned flesh filled the air.
"After it! Quick!" cried the doctor as he sprang forward.
BEFORE he could reach the prostrate creature it moved and then, slowly at first, but with rapidly gaining speed, it slithered over the floor in retreat. Dr. Bird's hand swung through an arc, and there was a deafening crash as a hand-grenade exploded on the back of the fleeing monster.
An unearthly scream came from the creature, and its motion changed from a steady forward glide to a series of convulsive jerks. Leffingwell and Carnes threw grenades, but they went wide of their mark, and the monster began to again increase its speed. Another volley of grenades was thrown and one hit scored, which slowed the monster somewhat but did not arrest the steady forward movement.
"Any more bombs?" demanded the doctor.
"Damn!" he cried as he received negative answers. "The current wasn't strong enough. It's going to get away." Carnes jerked his automatic from under his armpit and poured a stream of bullets into the fleeing monster. Slower and slower the motion of the creature became, and its movements again became jerky and convulsive.
"Keep it in sight!" cried the doctor. "We may get it yet!"
Cautiously the three men followed the retreating horror, Leffingwell pushing before him the platform holding the ultra-violet ray apparatus. The chase led them over familiar ground.
"There is the crack!" cried the lieutenant.
"Too late!" replied the doctor.
He rushed forward and seized the lower limb of the monster and tried with all his strength to arrest its flight, but despite all that he could do it slid sideways through the crack in the wall and disappeared. A final backward kick of its leg threw the doctor twenty feet against the far wall of the cave.
"Are you hurt, Doctor?" cried Carnes.
"No, I'm all right. Put on your masks and start the gas! Quick! That may stop it before it gets in far!"
THE three adjusted gas masks and thrust the mouths of two gas cylinders which were on the light truck into the crack, and opened the valves. The hissing of the gas was accompanied by thrashing, writhing sound from the bowels of the earth for a few minutes, but the sound retreated and
