I found three pockets on one wall, which seemed as if they must have been "salted" for my benefit; and in them, as elsewhere on my beach, the two extremes of life met. The topmost one, curiously enough, contained a small crab, together with a large water-beetle at the farther end. Both seemed rather self-conscious, and there was no hint of fraternizing. The beetle seemed to be merely existing until darkness, when he could fly to more water and better company; and the crab appeared to be waiting for the beetle to go. The next pocket was a long, narrow, horizontal fold, and I hoped to find real excitement among its aquatic folk; but to my surprise it had no bottom, but was a deep chute or socket, opening far below to the sand. However, this was not my discovery, and I saw dimly a weird little head looking up at me--a gecko lizard, which called this crevice home and the crabs neighbors. I hailed him as the only other backboned friend who shared the root-world with me, and then listened to a high, sweet tone, which came forth in swinging rhythm. It took some time for my eyes to become accustomed to the semi-darkness, and then I saw what the gecko saw--a big yellow-bodied fly humming in this cavern, and swinging in a small orbit as she sang. Now and then she dashed out past me and hovered in mid-air, when her note sank to a low, dull hum. Back again, and the sound rose and fell, and gained ten times in volume from the echo or reverberations. Each time she passed, the little lizard licked his chops and swallowed--a sort of vicarious expression of faith or desire; or was he in a Christian Science frame of mind, saying, "My, how good that fly tasted!" each time the dipteron passed? The fly was just as inexplicable, braving danger and darkness time after time, to leave the sunshine and vibrate in the dusk to the enormously magnified song of its wings. With eyes that had forgotten the outside light, I leaned close to the opening and rested my forehead against the lichens of the wall of wood. The fly was frightened away, the gecko slipped lower, seemingly without effort, and in a hollowed side of the cavernous root I saw a mist, a quivering, so tenuous and indistinct that at first it might have been the dancing of motes. I saw that they were living creatures--the most delicate of tiny crane-flies--at rest looking like long-legged mosquitoes. Deep within this root, farther from the light than even the singing fly had ventured, these tiny beings whirled madly in mid-air--subterranean dervishes, using up energy for their own inexplicable ends, of which one very interested naturalist could make nothing.