The influence of the kava-using peoples was more extensive in time and space than that of the betel-chewing people. Rivers supposes that they had neither clan organisation nor exogamy. Some of them preserved the body after death and respect was paid to the head or skull. It is possible that the custom of payment for a wife came into existence in Melanesia as the result of the need of the immigrant men for women of the indigenous people owing to their bringing few women with them, and the great development of shell money may be due in part to those payments. Contact with the earlier populations also resulted in the development of secret societies. The immigrants introduced the cult of the dead and the institutions of taboo, totemism and chieftainship. They brought with them the form of outrigger canoe and the knowledge of plank-building for canoes (which however was only partially adopted), the rectangular house, and may have known the art of making pile dwellings. They introduced various forms of currency made of shells, teeth, feathers, mats, etc., the drill, the slit drum, or gong, the conch trumpet, the fowl, pig, dog, and megalithic monuments. There may have been two immigrations of peoples who made monuments of stone: 1. Those who erected the more dolmen-like structures, probably had aquatic totems, and interred their dead in the extended position. 2. A later movement of people whose stone structures tended to take the form of pyramids, who had bird totems, practised a cult of the sun and cremated their dead.