Lazy quiverings were running through the mound of jelly, pulsings that gave evidence of its low organism. They saw little ripples of even beat run over it, and under them steady, sluggish convulsions that told of life; that showed, perhaps, that the thing was hungry and preparing to move its body in quest of food.

It was alive, unquestionably. The borer lay still, but this thing moved internally, of itself. It was life in its lowest, most primate form. The ma.s.s was mind, stomach, muscle and body all in one, stark and raw before their startled eyes.

"Oh, G.o.d!" Phil whispered through the long pause. "It can't be real!..."

"Protoplasm--a monster amoeba," David Guinness's curiously cracked voice said. "Just as it exists on the surface, only microscopically.

Primate life...."

The lock of the earth-borer clicked. Phil gasped. "Quade is coming out!" he said. A little cry of horror came from Sue. And the metal door opened.

James Quade stepped through, automatic in hand. He was fresh from the light inside, and he could not see well. He was quite unconscious of what was oozing down on him from above, of the flabby heap that was carefully stretching down for him. He peered into the gloom, looking for the three he had deserted, and all the time an arm from the ma.s.s above crept nearer. Sue Guinness's nerves suddenly gave, and she shrieked; but Quade's ears were deaf from the borer's thunder, and he did not hear her.

It was when he lifted one foot back into the sphere--probably to get out the searchlight--that he felt the thing's presence. He looked up--and a strange sound came from him. For seconds he apparently could not move, stark fear rooting him to the ground, the gun limp in his hand.

Then a surge ran through the mound of flesh, and the arm, a pseudopod, reached more rapidly for him.

It stung Quade into action. He leaped back, brought up his automatic, and fired at the thing once; then three times more. He, and each one of the others, saw four bullets thud into the heap of pallid matter and heard them clang on the metal of the sphere beneath. They had gone right through its flesh--but they showed no slightest effect!

Quade was evidently unwilling to leave the sphere. Jerking his arm up he brought his trigger finger back again. A burst of three more shots barked through the cavern, echoing and re-echoing. The man screamed an inarticulate oath as he saw how useless his bullets were, and hurled the empty gun at the monster--which was down on the floor now, and bunching its sluggish body together.

The automatic went right into it. They could all see it there, in the middle of the amorphous body, while the creature stopped, as if determining whether or not it was food. Quade screwed his courage together in the pause, and tried to dodge past to the door of the sphere; but the monster was alert: another pseudopod sprang out from its shapeless flesh, sending him back on his heels.

The feeler had all but touched Quade, and with the closeness of his escape, the remnants of his courage gave. He yelled, and turned and ran.

He ran straight for the three who watched from the tunnel mouth, and the mound of shapeless jelly came fast on his trail. It came in surging rolls, like thick fluid oozing forward; it would have been hard to measure its size, for each moment it changed. The only impression the four humans had was that of a wave of half-transparent matter that one instant was a sticky ball of viscid flesh and the next a rapidly advancing crescent whose horns reached far out on each flank to cut off retreat.

By instinct Phil jerked Sue around and yelled at the professor to run, for the old man seemed to be frozen into an att.i.tude of fearful interest. Bullets would not stop the thing--could anything? Holmes wondered. He could visualize all too easily the death they would meet if that shapeless, naked protoplasmic ma.s.s overtook and flowed over them....

But he wasted no time with such thoughts. They ran, all three, into the dark tunnel.

Quade caught up with them quickly. Personal enmity was suspended before this common peril. They could not run at full speed, for a mult.i.tude of obstacles hindered them. Tortuous ridges of rock lay directly across their path, formations that had been whipped in some mad, eon-old convulsion and then, through the ages, remained frozen into their present distortion; black pits gaped suddenly before them; half-seen stalagmites, whose crystalline edges were razor-sharp, tore through to their flesh. Haste was perilous where every moment they might stumble into an unseen cleft and go pitching into awful depths below. They were staking everything on the draft that blew steadily in their faces; Phil told himself desperately that it must lead to some opening--it must!

But what if the opening were a vertical, impa.s.sable tunnel? He would not think of that....

Old David Guinness tired fast, and was already lagging in the rear when Quade gasped hoa.r.s.ely:

"Hurry! It's close behind!"

Surging rapidly at a constant distance behind them, it came on. It was as fast as they were, and evidently untiring. It was in its own element; obstacles meant nothing to it. It oozed over the jagged ridges that took the humans precious moments to scramble past, and the speed of its weird progress seemed to increase as theirs faltered. It was a heartless ma.s.s driven inexorably by primal instinct towards the food that lay ahead. The dim phosph.o.r.escent illumination tinged its flabby tissues a weird white.

The pa.s.sage they stumbled through narrowed. Long irregular spears of stalact.i.tes hung from the unseen ceiling; others, the drippings of ages, p.r.o.nged up from the floor, shredding their clothes as they jarred into them. One moment they were clambering up-hill, slipping on the damp rock; the next they were sliding down into unprobed darkness, reckless of where they would land. They were aware only that the water-odorous draft was still in their faces, and the hungry mound of flesh behind....

"I can't last much longer!" old Guinness's winded voice gasped. "Best leave me behind. I--I might delay it!"

For answer, Phil went back, grabbed him by the arm and dragged his tired body forward. He was s.n.a.t.c.hing a glance behind to see how close the monster was, when Sue's frightened voice reached him from ahead.

"There's a wall here, Phil--and no way through!"

And then Holmes came to it. It barred the pa.s.sage, and was apparently unbroken. Yet the draft still came!

"Search for where the draft enters!" he yelled. "You take that side!"

And he started feeling over the clammy, uneven surface, searching frantically for a cleft. It seemed to be hopeless. Quade stood staring back into the gloom, his eyes looking for what he knew was surging towards them. His face had gone sickly white, he was trembling as if with fever, and he sucked in air with long, racking gasps.

"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 s.p.a.ce.

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 stalact.i.tes 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 b.l.o.o.d.y 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 impa.s.sable.

James Quade crumpled at the brink; "It's the end!" he moaned. "We can't go farther! It's the end of the draft!"

The hole blocked their forward path completely. They could not go ahead.... In seconds, it seemed, the slithering that told of the monster's approach sounded from behind. Sue's eyes were already fixed on the awful, surging ma.s.s when a voice off to one side yelled:

"Here! Quick!"

It was Phil Holmes. He had been scouting through the gloom, and had found something.

The other three ran to him. "There's another draft going through here," he explained rapidly, pointing to an angled crevice in the rocky wall. "There's a good chance it goes to the cavern where the sphere and the hole to the surface are. Anyway, we've got to take it.

I'd better go first, after this--and you, Quade, last. I trust you less than the monster behind."

He turned and edged into the crack, and the others followed as he had ordered. Quickly the pa.s.sageway broadened, and they found the going much easier than it had been before. For perhaps ten minutes they scrambled along, with the draft always on their backs and the blessed, though faint, fire of hope kindling again. In all that time they did not see their pursuer once, and the hope that they had lost it brought a measure of much needed optimism to drive their tired bodies onward.

They found but few time-wasting obstacles. If only the tunnel would continue right into the original cavern! If only their path would stay clear and unhindered!