He swung back his body and arm, aimed true for the spot behind the shoulders of the walrus, and then drove the iron home with all his strength. The harpoon sank deep, and a mighty roar burst from the lips of the stricken beast. Mark drove down the steel peg, stamping on it to fix it securely in the ice. The walrus threw his huge body around and came half out of the water upon the ice to reach his tormentor. But Jack was ready for this move, and he sprang back, out of danger, and picked up his rifle. The ice of course broke under the walrus for yards around. His fierce little eyes seemed to take in every move of his tormentors. He saw both boys (for Mark, too, had reached his gun) spreading out on either hand to get in fatal shots if they could. Meanwhile Washington White stood on the line close to the peg in the ice so that the beast could not jerk free. "Take him in the eye, if you can, Mark!" shouted Jack. "The cap of blubber he wears will act like a cushion if we shoot him in the head." But before either of them could obtain a satisfactory mark, the beast sank from sight. He had broken the ice for some yards toward the place where the end of the line was fastened, and he now had plenty of slack. The boys waited expectantly for his reappearance, while Wash stood, open-mouthed and eyes a-roll. Suddenly the black man executed a most astounding acrobatic feat. From that standing posture he executed in the twinkling of an eye a swift back somersault, at least twenty feet from the ice! "Oh, gollyation! I'se a goner!" he yelped, as he described his surprising parabola through the air. The ice where Wash had stood, and where the steel peg had been driven in, was crushed to fragments as the huge head and shoulders of the wounded walrus came up from the depths. The creature had marked the negro's position exactly, and had burst through the ice at the right spot. The wonderful lightness of all matter on this torn-away world, however, saved the darkey's life. The blow threw Wash so far away that the walrus could not immediately get at him. But he evidently laid his trouble entirely to the black man, and he threw himself forward along the ice, smashing it to bits, and gnashing at it with his tusks. In half a minute he would have been on the spot where the negro lay had not the boys run in swiftly and pumped a dozen bullets into his eyes and down his open mouth. By good luck more than good management they killed the beast. "See wot yo' done done!" wailed Washington White, rising gingerly and with a hand upon the small of his back. "Yo' come near ter spilein' Perfesser Henderson's most impo'tant assistant. How do you 'speck de perfesser c'd git erlong widout me?" This was certainly an unanswerable question, and the boys admitted it. They were sorry Wash had been so badly frightened, but they were delighted at the possession of the tusks of the walrus. The whalers secured the body, too, and made a very good quality of oil out of the blubber.