mA=_fB_                      mB=fA
_______|                            |_______
|      |                            |      |
[fB]     mB=_fA_                  fB=mA   [mB]
_________|                          |_________
|        |                          |        |
[fA]     mA=_fB_                  fA=mB     [fB]
_________|                          |_________
|        |                          |        |
[fB]     mB=_fA_                  fB=mA     [fA]
etc.                                etc.

We see from this that the alternate generations are in each group A and B, whose spouses are in the same alternation B and A, the male remaining in the group, the female removing in each case, if we assume that the matrilineal kinship is the rule.  The permanent members of each group therefore, and in like manner the imported members, are by alternate generations A and B, though of course there is no difference of age actually corresponding to the difference of generation.

By the simple phratry law that A can only marry B, and may marry any B, local group mates are marriageable.  The law however which forbids the marriage of phratry mates is on Mr Lang’s original theory founded on the prohibition to marry group mates.  If we suppose that the primal law or the memory of it continued to work, we have at once a sufficient explanation of the origin of the four-class system.  The tribes or nations in which the instinct against intra-group marriage was strong enough to persist as an active principle after the law against intra-phratry marriage had become recognised, may have proceeded to create four classes at a very early stage, while those in whom the feeling for the primal law was less strong adhered to the simple phratry system.

But it is an insuperable objection to this theory that it makes the four-class system originate simultaneously with, or at any rate shortly after, the rise of the phratries.  For we cannot suppose that the feeling for the primal law remained dormant for long ages and then suddenly revived.  On the other hand we have seen that if the difference in the distribution of the phratry and class names is any guide, a considerable interval must have separated the rise of the one from the rise of the other.  Unless therefore it can be shown that some other explanation accounts for the non-coincidence of phratry and class areas, we can hardly accept any explanation of the origin of classes which makes them originate at a period not far removed from the introduction of the phratries.

The fact that a certain number of class names are in character totemic, that is, bear animal names, suggests that the class system may be a development of the totem kins, which in certain cases are grouped within the phratries or otherwise subject to special regulations.  In the Urabunna the choice of a man of one totem is said to be limited to women of the right status in a single totem of the opposite