At the touch of a lever which lay under one of Dirk's hands the plane rose straight out of the water, and he maneuvered it directly over the top of the strange enigma. Then he touched a button and the pontoons were drawn up into the undercarriage of the craft. "Shall I make a landing on it?" he asked, turning his head and addressing Fragoni. The latter nodded his head, and Dirk dropped the ship gently onto the smooth surface of the monster, the pneumatic gearing completely absorbing the shock of the landing. Dirk relinquished the controls and, opening the door of the cabin, he stepped out onto the rough and pitted substance of which the leviathan was compounded. He stood there while the others came out after him. A large area on the top of the monster was perfectly flat and, within a very few moments, Dirk discovered that it was decidedly warm. He had brought the plane down close to the middle of the length of the strange craft in the belief that there, if anywhere, some indication of an entrance might be found. * * * * * The voice of Steinholt, tense with suppressed excitement, appraised him that his surmise had been correct. "There is a manhole of some sort," the electrical wizard exclaimed. "And look, it is turning!" They saw, not far ahead of them, a circular twelve-foot section of the deck slowly revolving, and, even as they watched, it commenced to rise slowly upward as the threads with which it was provided turned gradually around. Almost involuntarily they retreated a few feet and stood there, spellbound, as they stared at the massive, revolving section of the deck. It continued to turn until fully ten feet of the mobile cylinder had been exposed. Then the bottom of it appeared. Even then it continued to revolve and rise on a comparatively small shaft which supported it and, at the same time, thrust it upward. Dirk and his companions kept their eyes on the rim of the well which had been exposed, and awaited the appearance of something, they knew not what. When the top of the great cylinder was fully twelve feet above the deck of the craft it slowly ceased to revolve. Moment succeeded moment as the members of the little group rigidly and almost breathlessly awaited developments. Then Dirk, with an impatient ejaculation, stepped forward toward the yawning hole and cautiously peered over the edge of it. He stood there for a moment, as if transfixed, and then, with an exclamation of horror, retreated swiftly to where his friends were standing. * * * * * "What is it?" gasped Steinholt. "What did you see when--"