Tom was last, swimming along leisurely enough, and thinking about the mound and its hidden treasure,--as were all the other boys,--when suddenly he became aware of a movement in the water behind him, as of some living thing swimming. It was not any of the boys. They were all ahead; and it could not be Turnbull. It was not a man at all. In an instant a terrible thought came to him, that sent a pang of dreadful anguish through his inmost soul. A shark! That was the thought that flashed into Tom’s mind. Hastily and fearfully he turned his head, dreading the worst. One glance was enough. That glance froze his very life-blood with utter horror. There, not more than six or eight yards away, he saw a black muzzle on the surface of the water, pointing straight towards himself,--a muzzle narrow, and black, and horrible. Tom had never seen a shark; but he had read of them, and had seen pictures of them. One look was enough to convince him that this was a shark, who had scented them from afar, perhaps from the outer sea, and was now about to seize his prey. His brain whirled, and all the scene for an instant swam before his eyes. A half dozen yards! Could he hope to escape? Impossible! Yet, out of utter despair, there came to him the strength of a giant. He struck out with frantic and frenzied vehemence, shouting and screaming to the other boys,-- “A shark! a shark! a sha-a-a-a-a-a-a-ark!!!” The other boys heard his yells. They looked around and saw all--the ghastly face and staring eyes of Tom, with the horror of his expression, and beyond--the black muzzle. At that sight, there seized them all a terror equal to that of Tom. In any other position they would have sprung to his help. But what help was possible here? None. They were naked. They were unarmed. They were in the water. Helpless thus, and despairing, there was nothing which any one of them could do, but to swim blindly on. It was an instinct of self-preservation that animated them all. They fled as they would have fled from an earthquake, or a roaring torrent--blindly--in frantic haste. Not one word more was uttered. Not a sound was heard except the plashing noise of their movements through the water, and the heavy pantings of the exhausted swimmers. Still, though exhausted, not one of them dared to slacken his efforts. Not one of them dared to look around. In Tom’s mind there was the chilling horror of the monster behind, and a curdling dread of that moment when he would be seized. In the minds of the others there was an equal horror of expectation, as they listened to hear the yell from Tom, which might announce that all was over. Thus they hurried on.