Moreover, the clan is a society which is less able than any other to do without an emblem or symbol, for there is almost no other so lacking in consistency. The clan cannot be defined by its chief, for if central authority is not lacking, it is at least uncertain and unstable.[727] Nor can it be defined by the territory it occupies, for the population, being nomad,[728] is not closely attached to any special locality. Also, owing to the exogamic law, husband and wife must be of different totems; so wherever the totem is transmitted in the maternal line--and this system of filiation is still the most general one[729]--the children are of a different clan from their father, though living near to him. Therefore we find representatives of a number of different clans in each family, and still more in each locality. The unity of the group is visible, therefore, only in the collective name borne by all the members, and in the equally collective emblem reproducing the object designated by this name. A clan is essentially a reunion of individuals who bear the same name and rally around the same sign. Take away the name and the sign which materializes it, and the clan is no longer representable. Since the group is possible only on this condition, both the institution of the emblem and the part it takes in the life of the group are thus explained. It remains to ask why these names and emblems were taken almost exclusively from the animal and vegetable kingdoms, but especially from the former.