Animals and symbols correspond, therefore, to the same basic formulae, logically binary and even defended by the fact that animals of the same species appear frequently in pairs, male and female, though the dispositivo is so complex that we ought not suppose an explanation purely based in the symbolism of fertility; the first element is the presence of two species A-B (horse-bison); confronted with two types of signs, masculine and feminine, an attempt to attribute to the horse and bison the same symbolic value or, at least, a bivalency of the same kind as that of the symbols of the two categories (S1 and S2)[9]