Ahead the Rala boats were in flight toward their city, and now their pursuers were like sharks striking after them. There in the depths the force-guns of black and glittering boats alike were spitting, and giant waves and underwater convulsions rocked pursued and pursuers as the exploding shells annihilated boats and water about them. The tunnel! Its round opening yawned in the looming wall ahead, and Norman saw the Rala craft, reduced to scores in number, hurtling into it, to rouse all the forces of the great amphibian city. Their own boats were flashing into the opening after them. He glimpsed as he glanced back for a moment the larger craft with the great force-bombs veering aside behind them. It was nightmare in the water-tunnel. Flashing beams of the craft ahead and waters that rocked and smashed around them as in flight the Ralas still rained back force-shells toward them in a chaos of action. Once the frog-men turned to hold them back in the tunnel, but by sheer weight the rushing ships of the green men crashed them onward. Boats were going into nothingness all around them. A part of Norman's brain wondered calmly why they survived even while another part kept his gun again working, with refilled magazine. Fellows and Sarja were grotesque shapes beside him. Abruptly the tunnel curved upward and as they flashed up after the remaining Rala craft their boats ripped up into clear air! They were beneath the giant dome! The frog-men chased inward spread out in all directions over their mighty, swarming city and across it a terrific clamor of alarm ran instantly as the green men emerged after them! Norman saw flying-boats beginning to rise across all the city and realized that moments would see all the immense force of the Ralas, the thousands of craft they could muster, pouring upon them. He pointed out over the city to a block-like building, and shouted madly through his helmet to Fellows and Sarja: "Hackett!" But already Sarja had sent their craft whirling across the city toward the structure, half their fleet behind it, with part still emerging from the water-tunnel. Rala boats rose before them, but nothing could stop them now, their force-shells raining ahead to clear a path for their meteor-flight. They shot down toward the block-structure, and Norman, half-crazed by now, saw that to descend and enter was suicide in the face of the frog-forces rising now over all the city. He cried to Fellows, and with two of the guns as they swooped lower they sprayed force-shells along the building's side. * * * * *