The domes themselves were well ventilated through the large central air shaft and the numerous windows that pierced the outer walls at frequent intervals at each level above the ground floor, in which, as previously explained, there are but four openings. The windows, which were six and one-quarter inches wide by eighteen and a half inches high, admitted a certain amount of light as well as air; but the interior of the dome, especially the gloomy chambers mid-way between the windows and the central light and air shaft, was illuminated by immense, slow-burning, smokeless candles. Tarzan watched the construction of the new dome with keenest interest, realizing that it was the only opportunity that he ever would have to see the interior of one of these remarkable, human hives, and as he was thus engaged Komodoflorensal and his friends hastened to initiate him into the mysteries of their language; and while he learned the language of his hosts he learned many other things of interest about them. The slaves, he discovered, were either prisoners of war or the descendants of prisoners of war. Some had been in bondage for so many generations that all trace of their origin had become lost and they considered themselves as much citizens of Trohanadalmakus, the city of King Adendrohahkis, as did any of the nobility. On the whole they were treated with kindness and were not overworked after the second generation. The recent prisoners and their children were, for the most part, included in the caste of unskilled labor from which the limit of human endurance was exacted. They were the miners, the quarriers and the builders and fully fifty per cent of them were literally worked to death. With the second generation the education of the children commenced, those who showed aptitude for any of the skilled crafts being immediately transferred from the quarries to the domes, where they took up the relatively easy life of a prosperous and indulged middleclass. In another manner might an individual escape the quarries--by marriage, or rather by selection as they choose to call it, with a member of the ruling class. In a community where class consciousness was such a characteristic of the people and where caste was almost a fetish it was rather remarkable that such connections brought no odium upon the inferiors, but, on the contrary, automatically elevated the lesser to the caste of the higher contracting party.