But if we replace individual marriage, we can then grasp the apparent excess of cases of incest shunning which we have met among these same races. The totem exogamy, or prohibition of sexual intercourse between members of the same clan, seemed the most appropriate means for the prevention of group incest; and this totem exogamy then became fixed and long survived its original motivation. Although we believe we understand the motives of the marriage restrictions among the Australian savages, we have still to learn that the actual conditions reveal a still more bewildering complication. For there are only few tribes in Australia which show no other prohibition besides the totem barrier. Most of them are so organized that they fall into two divisions which have been called marriage classes, or phratries. Each of these marriage groups is exogamous and includes a majority of totem groups. Usually each marriage group is again divided into two subclasses (subphratries), and the whole tribe is therefore divided into four classes; the subclasses thus standing between the phratries and the totem groups. The typical and very often intricate scheme of organization of an Australian tribe therefore looks as follows: [Illustration] The twelve totem groups are brought under four subclasses and two main classes. All the divisions are exogamous[15]. The subclass c forms an exogamous unit with e, and the subclass d with f. The success or the tendency of these arrangements is quite obvious; they serve as a further restriction on the marriage choice and on sexual freedom. If there were only these twelve totem groups--assuming the same number of people in each group--every member of a group would have 11/12 of all the women of the tribe to choose from. The existence of the two phratries reduces this number to 6/12 or 1/2; a man of the totem [Greek: α alpha] can only marry a woman from the groups 1 to 6. With the introduction of the two subclassess the selection sinks to 3/12 or 1/4; a man of the totem [Greek: α alpha] must limit his marriage choice to a woman of the totems 4, 5, 6.