After considering the foregoing data it seems impossible not to conclude that it must have taken centuries of time for the idea of duality, or of the Above and Below to have taken such a deep hold upon the native mind and to have produced such a growth of symbolism and association in so many ramifications of thought. Let us endeavor to obtain a further insight into the native mode of thought by carefully studying some significant details concerning the social organization of the Mexicans from the time of Acamapichtli to that of Montezuma and the influences it had been subjected to gradually. This, the first ruler, unquestionably ruled as the Cihuacoatl, a name which means either Woman-serpent or Female-twin. This fact in itself testifies to an epoch-making change in the organization of the Mexican government, in the making of which a concession was made to a previously existing order of things, by the retention of the female title by a male ruler. Having carefully studied the question for many years, I have long considered it proven that when the Mexicans settled in the valley of Mexico they came under a series of influences emanating from an ancient and highly cultured centre of civilization situated in the south, which had followed, during untold centuries, the same lines of primitive thought which have been stated. This question of contact and influence from an older civilization is so important and the material I have collected on the subject is so extensive and complex, that it cannot be adequately treated here. Further on I shall discuss at length certain historical data throwing light on ancient contact and influences. Meanwhile I may as well state here that, having carefully weighed all testimony, I accept as amply proven and well supported, the testimony of Las Casas, Torquemada, Mendieta and others, who record that the Mexican culture-hero Quetzalcoatl was an actual person who had come to Mexico from Yucatan twice and had finally returned thither, leaving a small colony of his vassals behind him whose influence upon the religious and social organization and symbolism of the tribes, inhabiting the central plateau, can be plainly discerned. Montezuma himself, in his famous speech to Cortés, which the latter carefully reported to the Emperor Charles V, states that: “we [the Mexican rulers] were brought here by a lord, whose vassals all of our predecessors were, and who returned from here to his native land. He afterwards came here again, after a long time, during which many of his followers who had remained, had married native women of this land, raised large families and founded towns in which they dwelt. He wished to take them away from here with him, but they did not want to go, nor would they receive or adopt him as their ruler, and so he departed. Hut we have always thought that his descendants would surely come to subjugate this country and claim us as their vassals....” (Historia de Nueva España. Hernan Cortés, ed. Lorenzana, p.