For a few seconds no one knew what to do. To rush in to the rescue of the boys would have been foolhardy, as the terrible octupus, which they knew had grabbed the lads, would have been a match for all of the adventurers, unarmed as they were. It would be necessary to return to the ship and come back with some of the electric guns, which they had neglected to bring with them. In the meanwhile the beast might, and probably would, kill Mark and Jack. But there was nothing else to do. The professor motioned for Andy to remain on the watch at the mouth of the cavern, so as to be on hand in case he could help the boys, while the others were hurrying toward the ship. Then, leading the way, the Professor signalled for Tom and Bill to follow him. They could not hurry much for the heavy suits and the resistance of the water impeded their progress. But they made all the speed they could, urged on by a terrible fear. Meanwhile old Andy stood in front of the cave, hoping against hope that there might be some way of aiding the boys. If it had happened above water he would not have hesitated to rush in and give battle to the beast, even though he was unarmed. If he had his knife now he would venture in, at the risk of his life. "Oh, why didn't I bring my gun along!" thought Andy regretfully. His hand dropped to his side and his fingers came in contact with a big knife in the belt of the diving suit. Here was a weapon he had forgotten all about. He drew forth the blade. It seemed a small one with which to attack so large and terrible a creature as the octupus. Yet to remain there, knowing the boys were being killed was more than old Andy could stand. Grasping the handle with a firm grip he started toward the cave. His foot caught in something, and he nearly fell. Looking down to see what had tripped him he saw a long thin pole, straight as a lance. It had once been a tree limb, but all the branches were stripped off. "Now if I only had an iron point for that," Andy thought. Then he recollected the knife in his hand. "The very thing," he remarked aloud, the words sounding startlingly loud in the confinement of the copper helmet. "If I only had something to fasten the knife on the pole I could make a spear to attack the octupus." Then he saw long streamers of sea weed growing up from the ocean bed. They were very tough, a kind of wirey grass that was as strong as rope. Andy cut several streamers and, with a hunter's skill bound the knife to the end of the staff. Now he had a weapon formidable enough to venture in and give battle to the monster. He hesitated no longer, fearing that even the short delay might have been too much and that the boys were dead. He entered the cave. At first he could perceive nothing for it was quite dark. Then, as his eyes became used to the gloom, which the lamp in his helmet faintly illuminated, he saw, far back in the rear, the horrible octupus.