But this conclusion presupposes that the tribes of which we have just been speaking admit the doctrine of reincarnation. Now according to Strehlow, this doctrine is unknown to the Arunta, the society which Spencer and Gillen have studied the longest and the best. If, in this particular case, these two observers have misunderstood things to such an extent, their whole testimony would become suspect. So it is important to determine the actual extent of this divergence. According to Strehlow, after the soul has once been definitely freed from the body by the rites of mourning, it never reincarnates itself again. It goes off to the isles of the dead, where it passes its days in sleeping and its nights in dancing, until it returns again to earth. Then it comes back into the midst of the living and plays the rôle of protecting genius to the young sons, or if such are lacking, to the grandsons whom the dead man left behind him; it enters their body and aids their growth. It remains thus in the midst of its former family for a year or two, after which it goes back to the land of the souls. But after a certain length of time it goes away once more to make another sojourn upon earth, which is to be the last. A time will come when it must take up again, and with no hope of return this time, the route to the isles of the dead; then, after various incidents, the details of which it is useless to relate, a storm will overtake it, in the course of which it will be struck by a flash of lightning. Thus its career is definitely terminated.[792] So it cannot reincarnate itself; nor can conceptions and births be due to the reincarnation of souls which periodically commence new existences in new bodies. It is true that Strehlow, as Spencer and Gillen, declares that for the Arunta commerce of the sexes is in no way the determining condition of generation,[793] which is considered the result of mystic operations, but different from the ones which the other observers told us about. It takes place in one or the other of the two following ways: