In northern Luzon, I hold, we find evidences of at least two series of waves and periods of migration, the members of which are similar physical type and language. It appears, however, that they came from somewhat different localities of southeastern Asia and had, in their old homes, developed social organizations and other elements of culture radically different from one another--institutions and groupings which they brought with them to the Philippines, and which they have maintained up to the present time. To the first series belong the Igorot [1] with their institutions of trial marriage; division of their settlements into social and political units known as _ato_; separate dormitories for unmarried men and women; government by the federated divisions of a village as represented by the old men; and a peculiar and characteristic type of dwelling. In the second wave series we find the Apayo, the western division at least of the people known as Kalinga, the Tinguian, and Ilocano. [2] In none of these groups do we find the institutions just mentioned. Trial unions are unknown, and marriage restrictions are based solely on blood relationship; government is through the headman aided by the elders of his village, or is a pure democracy. Considerable variation exists between the dwellings of these four peoples, yet they conform to a general type which is radically different from that of the Igorot. The Apayao and Kalinga divisions of this second wave series, by reason of their environment, their more isolated localities and consequent lack of frequent communication with the coast, have a simpler culture than that of the Tinguian; yet they have, during many generations, developed certain traits and institutions now apparently peculiar to them. The Tinguian and Ilocano, on the other hand, have had the advantages of outside communication of extensive trade, and the admixture of a certain amount of foreign blood. These last two groups evidently left their ancient home as a unit, at a time prior to the Hindu domination of Java and Sumatra, but probably not until the influence of that civilization had begun to make itself felt. Traces of Indian culture are still to be found in the language, folklore, religion, and economic life of this people, while the native script which the Spanish found in use among the Ilocano seems, without doubt, to owe its origin to that source. After reaching Luzon, this people slowly broke up into groups which spread out over the provinces of Ilocos Sur and Norte, Union and Abra. The partial isolation of some of these divisions, local feuds, the universal custom of head-hunting, and the need of human victims to accompany the spirits of the dead, all doubtless aided in separating the tribe into a number of dialect groups,--groups which nevertheless retained the old culture to a surprising degree.