Beneath us there lay the very edge or dividing line between the dark and sunlit sides, a belt of twilight dusk that was very narrow. Squarely across that belt, we saw, there lay beneath us a great compartment that was largest by far of all that we had yet seen, and that was unique among them in that, instead of being rectangular, it was circular in shape. Down, over and past this mighty circular compartment our cylinders were speeding, and we could but vaguely note some circular object inside it, when we were past it, were speeding low over the thronged and busy compartments of the sunward side. Rapidly the speed of the cylinders decreased, and then they had paused in mid-air, were beginning to descend. And in a moment more they had come smoothly to rest in a great rectangular compartment which seemed reserved as a landing-place, since on it there rested scores of other cylinders, others constantly arriving or departing. Later we were to learn that these landing-compartments were scattered in large number over Triton's surface, on the sunlit and dark sides both. For the present moment, though, Marlin and I were gazing only at our immediate surroundings. As we landed the guards on either side of us gripped us tightly, the others keeping their tubes pointed toward us, and then, as the throbbing of the cylinder's generators ceased, the Neptunian leader of the crimson-circle insignia uttered a staccato order. At once our guards were thrusting us toward the ladder that led downward, and, holding us above and beneath, were descending that ladder with us into the cylinder's lowest compartment. There the Neptunian leader followed us in a moment, and as the cylinder's door was slid open a flood of warm, heavy air and a babel of sound from about us rolled inside. Before emerging, though, the Neptunians performed an action that for the moment puzzled me completely.