I will first ask you to consider to what kind of psychological similarity such a practice can be due. What kind of psychological similarity can there be between one special kind of cousin and the father, and between another special kind of cousin and a son or daughter? If the puzzle as put in this form does not seem capable of a satisfactory answer, let us turn to see if the Banks Islanders practise any social custom to which this peculiar terminology can have been due. In the story of Ganviviris told to Dr. Codrington in these islands[12] an incident occurs in which a man hands over one of his wives to his sister’s son, or, in other words, in which a man marries one of the wives of his mother’s brother. Inquiries showed, not only that this form of marriage was once widely current in the islands, but that it still persists though in a modified form. The Christianity of the natives does not now permit a man to have superfluous wives whom he can pass on to his sister’s sons, but it is still the orthodox, and indeed I was told the popular, custom to marry the widow of the mother’s brother. It seemed that in the old days a man would take the widow of his mother’s brother in addition to any wife or wives he might already have. Though this is no longer allowed, the leaning towards this form of marriage is so strong that after fifty years of external influence a young man still marries the widow of his mother’s brother, sometimes in preference to a girl of his own age. Indeed, there was reason to believe that there was an obligation to do so, if the deceased husband had a nephew who was not yet married. The peculiar features of the terminology of relationship in these islands are exactly such as would follow from this form of marriage. If, in Diagram 2, _C_ marries _b_, the wife or widow of his mother’s brother, and thereby comes to occupy the social position of his uncle _A_, the children of the uncle, _D_ and _e_, will come to stand to him in the relation of children, while he, who had previously been the father’s sister’s son of _D_ and _e_, will now become their father. An exceptional form of the classificatory system, in which there is a departure from the usual rule limiting a term of relationship to members of the same generation, is found to be the natural consequence of a social regulation which enjoins the marriage of persons belonging to different generations. [12] _Op. cit._, p. 384.