This phenomenon, moreover, is but the anthropological expression of a more general biological law, in virtue of which human races, in order to adapt themselves to the medium in which they are developed, assume a uniform physical type and character, which persists, or repeats itself anatomically and psychically through the ages, in spite of the external forms of their civilization; in the same way as do other animals, and plants. Thus, for example, since the days of Trajan the bullocks of the Danube have had enormous and diverging horns; in China the cattle are hump-backed, despite cross-breeding with other strains; and, although the first offspring from crossing may be like the foreign parent, in the fifth or sixth generation there appears in the _creole_ calf the hump of the original and native form. Among the ancient _castas_ of the vice-reinal society the _negro_ was seen to reappear in families of white, or even of red parentage, provided there had been blacks in the ancestry. In the waters of the Nile, the lotus yet floats its blue corolla, which the architects of Memphis copied in the capitals of their temples; and the Fellah of Pharaonic days reappears in families crossed with the Macedonians of the Ptolemies; and, in the first centuries of the Arab domination, in spite of the torrents of foreign blood introduced by polygamy. Even today the type reasserts itself in the native regiments of the English army at Cairo--bronzed, titanic, full-chested, a living model, which is copied in the colossi of Isamboul and which is the ethnic brother type of the Rameses and Amenhotep. In the central tableland of Mexico, arid, hot, and luminous, where the atmosphere keeps the nerves at high tension; where thoughts are clouded by the abuse of tobacco, of alcohol and of coffee; by the irritation of an eternal and fruitless battle for life; and, until lately, by the frightful impossibility, almost age-long, of forming a plexus of social solidarity; character, in the greater part of society has degenerated and the ferocious tendencies of the Aztecs have reappeared. After ten generations, there has returned, to beat within the breasts of some of our compatriots, the barbaric soul of the worshipers of Huitzilopochtl, of those of _the sacred springtimes_ who went, to the lugubrious sounds of the _teponastl_ to make razzias of prisoners in Tlaxcala and Huejotzinco, to open their breasts with obsidian knives, to tear out the heart and eat it in the holocaust of their gods. Three centuries of masses and of barracks have been too little for the complete evolution of character among the people; and if, on the Silesian plain, the Sarmatian of Attila yet appears, so too in our political struggle there has re-appeared, with the indomitable warrior of Ahuitzotl, the sanguinary priest of Huitzilopochtl.