I have taken this case somewhat out of its proper place in my argument because the evidence is so closely connected with that by means of which I have shown the relation between features of systems of relationship and peculiar forms of marriage in Melanesia. I have now to return to the more sober task of considering how far we are justified in inferring the former existence of marriage institutions when we find features of systems of relationship of which they would have been the natural consequence. It is evident that, whenever we find such a feature as common nomenclature for a grandmother and a sister or for a cross-cousin and a parent, it should suggest to us the possibility of such marriage regulations as those of Pentecost and the Banks Islands. But such common designations might have arisen in some other way, and in order to establish the existence of such forms of marriage in the past history of the people, we must have criteria to guide us when we are considering whether a given feature of the terminology of relationship is or is not a survival of a marriage institution. I will return to the cross-cousin marriage for my examples. The task before us is to inquire how far such features of relationship as exist in Fiji, Anaiteum or Guadalcanar, in conjunction with the cross-cousin marriage, will justify us in inferring the former existence of this form of marriage in places where it is not now practised. If there be found among any people all the characteristic features of a coastal Fijian or of an Anaiteum system, I think few will be found to doubt the former existence of the cross-cousin marriage. It would seem almost inconceivable that there should ever have existed any other conditions, whether social or psychological, which could have produced this special combination of peculiar uses of terms of relationship. It is when some only of these features are present that there will arise any serious doubt whether they are to be regarded as survivals of the former existence of the cross-cousin marriage. One consideration I must point out at once. Certain of the features which follow from the cross-cousin marriage may be the result of another marriage regulation. In some parts of the world there exists a custom of exchanging brothers and sisters, so that, when a man marries a woman, his sister marries his wife’s brother. As the result of this custom the mother’s brother and the father’s sister’s husband will come to be one and the same person, and the father’s sister will become also the mother’s brother’s wife.