The system of two classes is not only found near Mount Gambier in South Australia, but also farther east along Darling River, and in the northeast of Queensland. It is, consequently, widespread. It excludes only marriage between brothers and sisters, between brothers' children and between sisters' children of the mother's side, because these belong to the same class; but the children of a sister can marry those of a brother and vice versa. A further step for preventing inbreeding is found among the Kamilaroi on the Darling River in New South Wales, where the two original classes are split into four, and every one of these is married as a whole to a certain other class. The first two classes are husbands and wives by birth. According to the place of the mother in the first or second class, the children belong to the third and fourth. The children of these two classes, who are also married to one another, again belong to the first and second class. So that a certain generation belongs to the first and second class, the next to the third and fourth and the following again to the first and second. Hence the children of natural brothers and sisters (on the mother's side) cannot marry one another, but their grandchildren can do so. This peculiarly complicated order of things is still more entangled by the inoculation--evidently at a later stage--with maternal law gentes. But we cannot discuss this further. Enough, the desire to prevent inbreeding again and again demands recognition, but feeling its way quite spontaneously, without a clear conception of the goal.