A stringent requirement of the _kiva_ form is that it should be at least partly subterranean, so it is of necessity entered only by a ladder thrust down from the top through a hatchway. The more primitive form of the _kiva_ is circular, but at Ácoma it is described as rectangular, because, owing to the conditions enforced by a rocky table land, the _kiva_ here became a part of the lowest storey of the house-block, hollowed somewhat deeper into the rock to meet the religious requirement. The curious orifice in the _kiva_, called Si-pa-pu, represents the place from which human beings originally emerged, and the peculiar arrangement of the floor within the _kiva_ suggested to Mr. Mindeleff that it perhaps typified the four worlds of the genesis-myth, and the “four houses” of the creation myths. The Si-pa-pu with its cavity beneath the floor indicates the lowest house under the earth—the abode of the Creator, Myuinga. The main or lower floor represents the second stage where Light came; the elevated section of the floor, the third stage where animals were created. Upon this platform animal-fetiches are set in groups at New Year festivals. It is also to be noted that the ladder to the surface is always of pine and always rests on the platform, never on the lower floor. In their traditional genesis, the people climbed from the third house by means of a tree or a ladder of pine through such an opening as the _kiva_ hatchway to the outer air, or the fourth world.[29] The _kiva_ has also been called the nearest approach that the Indian had to a school-house for the boys of the tribe. There, during the long winter evenings, the old men—tellers of tales—would sit wrapped in their many-colored blankets and recite their legends; it might be the story of their origin and their wanderings, or the blood-curdling relation of how their peaceful life was broken in upon by the dreaded Comanches or the Navajos; and then, again, by the invading white men, who came on strange four-footed beasts, filling the souls of the Ancients with terror and awe. Out of such long-spun tales, from the poetry of nature to the massacre of their “nations,” the wondering boys would gradually learn the tribal lore of their people and the mystery of their religious traditions, which could be transmitted only word by word from the elders to the growing generation. Morgan tells us that, at Taos, the special duty of this all-important instruction was given to three old men. Regarding Ácoma, we have no definite information.