"Here! I have it!" cried the girl suddenly at her end of the wall. The other three ran over, and saw, just above her head, a narrow rift in the rock, barely wide enough to squirm through. "Into it!" Phil ordered tersely. He grasped her, raised her high, and she wormed through. Quade scrambled to get in next, but Holmes shoved him aside and boosted the old man through. Then he helped the other. A second after he had swung himself up, a wave of whitish matter rolled up below, hungry pseudopods reaching for the food it knew was near. It began to trickle up the wall.... * * * * * The crack was narrow and jagged; utterly black. Phil could hear Quade frantically worming himself ahead, and he wondered achingly if it would lead anywhere. Then a faint, clear voice from ahead rang out: "It's opening up!" Sue's voice! Phil breathed more easily. The next moment Quade scrambled through; dim light came; and they were in another vast, ghostly-lit cavern. The crack came out on its floor-level; Guinness was resting near, and his daughter had her hands on a large boulder of rock. "Let's shove it against the hole!" she suggested to Phil. "It might stop it!" "Good, Sue, good!" he exclaimed, and at once all four of them strained at the chunk, putting forth every bit of strength they had. The boulder stirred, rolled over, and thudded neatly in front of the crack, almost completely sealing it. There was only a cleft of five inches on one side. But their expression of relief died in their throats. A tiny trickle of white appeared through the niche. The amorphous monster was compressing itself to a single stream, thin enough to squeeze through even that narrow space. They could not block it. They had nothing to attack it with. There was nothing to do but run.... And hope for a chance to double back.... As nearly as they could make out, this second cavern was as large as the first. They could dimly see the fantastic shapes of hundreds of stalactites hanging from the ceiling. Clumps of stalagmites made the floor a maze which they threaded painfully. The strong steady draft guided them like a radio beacon, leading them to their only faint hope of escape and life. Guinness, very tired, staggered along mechanically, a heavy weight on Phil's supporting arm; James Quade ran here and there in frantic spurts of speed. Sue was silent, but the hopelessness in her eyes tortured Phil like a wound. His shirt had long since been ripped to shreds; his face, bruised in the first place by the borer he had crashed in, now was scratched and bloody from contact with rough stalagmites. * * * * * Then, without warning, they suddenly found among the rough walls on the far side of the cavern, the birthplace of the draft. It lay at the edge of the floor--a dark hole, very wide. Black, sinister and clammy from the draft that poured from it, it pierced vertically down into the very bowels of the earth. It was impassable.