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70 organisation. We have here so close a parallelism between two series of social phenomena as to supply as good an example as could be wished of the application of the method of concomitant variations in the domain of sociology.

The nature of these changes and their relation to the general cultures of the peoples who use the different forms of terminology show that the transitions are to be associated with a progressive change which has taken place in Oceania. In this part of the world the classificatory system has been the seat of a process of simplification starting from the almost incredible complexity of Pentecost and reaching the simplicity of such systems as those of Eddystone or Mekeo. This process has gone hand in hand with one in which the regulation of marriage by some kind of clan-exogamy has gradually been replaced by a mechanism based on relationship as traced by means of pedigrees.

If this conclusion be accepted, it will follow that the more widely distributed varieties of the classificatory system of relationship are associated with a social structure which has the exogamous social group as its essential unit. This position has only to be stated for it to become apparent how all the main features of the classificatory system are such as would follow directly from such a social structure. Wherever the classificatory system is found in association with a system of exogamous social groups, the terms of relationship do not apply merely to relatives with whom it is possible