s apart, in which by adoption he passes out of it and joins another
by means of a legal fiction[2]. The other kind of association, to which
the name _age-grades_ is applied, is composed of a series of grades,
through which, concomitantly with the performance of the rites of
initiation obligatory on every male member of the community, each man
passes in succession, until he attains the highest. In the rare cases
where an individual fails to qualify for the grade into which his
coevals pass, and remains in the grade of "youth" or even lower grades,
he is by birth a member of one class and does not remain outside the
age-grades altogether.

In the element of voluntary action lies the distinction between
age-grades and _secret societies_, which are organised on identical or
similar lines but depend for membership on ceremonies of initiation,
alike in the lowest as in the highest grade. Such societies may be
termed voluntary. The differentia between the natal and the voluntary
association lies in the fact that in the former all are members of one
or other grade, in the latter only such as have taken steps to gain
admission, all others being simply non-members.

Although _prima facie_ all these forms of association are equally
entitled to be classed as social organisations, the use of this term is
limited in practice, at any rate as regards Australia, and is the
accepted designation of the kinship form of natal associations only; for
this limitation there is so far justification, that though they perhaps
play a smaller part in the daily life of the people than the secret
societies of some areas, with their club-houses and other features which
determine the whole form of life, the kinship associations are normally
regulative of marriage and thus exercise an influence in a field of
their own.

Marriage prohibitions in the various races of mankind show an almost
endless diversity of form; but all are based on considerations either of
consanguinity or kinship or on a combination of the two. The distinction
between _consanguinity_ and _kinship_ first demands attention; the
former depends on birth, the latter on the law or custom of the
community, and this distinction is all-important, especially in dealing
with primitive peoples. With ourselves the two usually coincide, though
even in civilised communities there are variations in this respect.
Thus, according to the law of England, the father of an illegitimate
child is not aki