The scene before us was one of unequaled interest and activity. Over the masses of huge, shining buildings were flitting great swarms of the long black cones, moving from roof to roof, while in the shining streets below them moved other hordes of active figures, the people of the city. And as our eyes took in these latter I think that we all felt something of horror, in spite of all the alien forms which we were familiar with in the thronging worlds of the Galaxy. For in these creatures was no single point of resemblance to anything human, nothing which the appalled intelligence could seize upon as familiar. Imagine an upright cone of black flesh, several feet in diameter and three or more in height, supported by a dozen or more smooth long tentacles which branched from its lower end--supple, boneless octopus-arms which held the cone-body upright and which served both as arms and legs. And near the top of that cone trunk were the only features, the twin tiny orifices which were the ears and a single round and red-rimmed white eye, set between them. Thus were these beings in appearance, black tentacle-creatures, moving in unending swirling throngs through streets and squares and buildings of their glowing city. Helplessly we stared upon them, from our place of concealment. To venture into sight, I knew, would be to court swift death. I turned to Hurus Hol, then started as there came from the city ahead a low, waxing sound-note, a deep, powerful tone of immense volume which sounded out over the city like the blast of a deep-pitched horn. Another note joined it, and another, until it seemed that a score of mighty horns were calling across the city, and then they died away. But as we looked now we saw that the shining streets were emptying, suddenly, that the moving swarms of black tentacle-creatures were passing into the pyramidal buildings, that the cones above were slanting down toward the roofs and coming to rest. Within a space of minutes the streets seemed entirely empty and deserted, and the only sign of activity over all the city was the hovering of a few cones that still moved restlessly above it. Astounded, we watched, and then the explanation came suddenly to me. "It's their sleep-period!" I cried. "Their night! These things must rest, must sleep, like any living thing, and as there's no night on this glowing world those horn-notes must signal the beginning of their sleep-period." Hurus Hol was on his feet, his eyes suddenly kindling. "It's a chance in a thousand to get inside the city!" he exclaimed. The next moment we were out of the shelter of our concealing trees and were racing across the stretch of ground which separated us from the city. And five minutes later we were standing in the empty, glowing streets, hugging closely the mighty sloping walls of the huge buildings along it.