"I don't know," Mac admitted. The first ten lines halted within a foot of the flashing barricade. The next nine marched forward and mounted the backs of the first lines. Then each succeeding rank climbed those in front. "A pyramid!" Al yapped. The fishmen gaped up at Mac, then back at the 'pedes. They were close to cracking. "Wait!" Mac ordered. "Wait till boss-limpy says they're almost to the top of the fence. Then fire low. Don't keep firing after the pyramid falls!" The sporadic firing ceased. Immense gaps had appeared in the pyramid, but the fence had heated red. The drain on the generators would be enormous, and this MacAloon had feared more than the few invaders that might drop across. Swiftly, the pyramid grew until it was as high as the fence. Then, up in the lookout room, Limpy barked a signal. Flame leaped out at the lowest line of 'pedes, slashed back and forth. All in an instant, the pyramid collapsed. The centaurpedes retreated, leaving a ring of charred bodies around the fence. But the survivors were as numberless as ever. In the sudden silence, agonized shrieks rang out across the compound. "What's wrong, Limpy?" demanded MacAloon. "It's Al, but I can't see what happened!" "Stay where you are, Swede!" Mac ordered. "Keep the fishmen fighting!" He raced to Birchall's station, saw that Al's flame-thrower had jammed. Hundreds of centaurpedes had hurled themselves over the fence and surrounded two natives. Others had brought up a tree trunk and hammered a big hole in the wire. Through the gap, a full regiment was pouring into the enclosure. "Take care of the ones inside!" Al shrieked. "I'll stop them!" "Don't be a fool!" shouted Mac. "Fall back and get another flame-thrower!" Unheeding, Al smashed a path to the fence with the butt of his weapon. 'Pedes were already climbing up his body and wasting no time. He bit his lip and charged on. The trickle of blood running down his chin was the smallest one flowing from his torn flesh. In a last desperate lunge, he grabbed the ends of the broken fence. "_Al!_" Mac cried out. He was too late. A sheet of blue flame had sprung up. There was a piercing scream of pain beyond endurance. Then Birchall hung limply, caught, as he had intended, by the jagged ends of wire. His mangled, lifeless body, through which the current flowed, had closed the gap. * * * * * A sudden film spoiled Mac's vision. Savagely, he blinked it away. With vicious fury, he burned down the swiftly crawling centaurpedes around him. The two fishmen, no longer surrounded, shuddered free of their fright and began to help. Under the fierce heat, all the animals in the enclosure curled and died. Murderously calm, Mac fired a steady blast through the fence at the pyramid outside. Sizzling and frying, the formation fell to the ground.