The professor motioned for Bill and Tom to move behind him, and signalled for Jack, Mark and Andy to stand close with their weapons ready. The sharks floated lazily downward as if they knew they had the diggers at their mercy. To run and escape was impossible, for no one could run hampered by the weight of water and his diving suit. One of the terrible fish opened its mouth wider and, with a flirt of its tail aimed straight for the professor. Mr. Henderson raised his gun, and took careful aim at the middle of the fish, half turned over. Unerringly the electric bullet sped on its way. It entered the soft under part of the shark, and immediately the thing struggled in its death agony. The water was dyed with blood. At the same instant the other sharks rushed forward in a swirl of foam. The boys and Andy fired as best they could, and must have hit one of the creatures for there was a greater commotion. But the fight was not over. Instantly the ocean seemed alive with the giant fish. Attracted by the blood of the killed ones, scores of the tigers of the seas rushed toward the scene of combat making matters livelier than ever. The professor, the boys and Andy fired their guns at random. Redder and more red became the water until their helmet lamps barely glowed in the crimson sea. It seemed that a whole army of the voracious sharks had attacked them. The professor realized that to stay and attempt to fight all the sharks in that part of the ocean was impossible. He motioned for the boys and Andy to follow him. Then he slowly led the way back to the ship. But the sharks were not to be gotten rid of so easily. Several of the largest followed the diggers, their horrible eyes, and big mouths with rows of cruel teeth, striking terror to the hearts of all. One of the creatures made a rush for Bill and Tom who were close together. Either or both of the men would have been bitten in twain, in spite of the protection of their diving suits, had not Mark, with a snap shot, killed the fierce fish. It was now a running fight, and yet not so much that, because to run was impossible. However, they hurried all they could, and, by dint of quick firing kept the ugly creatures at bay until the side of the ship, where the diving tank was placed, was reached. The professor stepped to one side, and motioned for the others to proceed him in entering. Little time was lost. As Bill, the last one in, stepped past the steel door the inventor attempted to enter. To do so he had to let go of his gun. Instantly one of the sharks made a rush for the old man. But Andy was on the watch. He leaned forward, and, from his weapon sent a bullet straight down the throat of the monster. The electric missile did its work well, and the lifeless body of the shark was devoured by the others of its tribe. The professor pulled the door shut behind him. Then he set the pump to work to empty the tank. As he did so there was a tremor to the ship. What could it mean?