256 HERBERT SPENCER

Moreover, since the biologist has not yet arrived at
a clear conception of the innermost secret of the
individual organism, notably the secret of its unity,
the comparison implied in the metaphor of the social
organism is an attempt to interpret olscurum per
obscurius. The analogy, such as it is, is probably
destined to be of more use to the biologist than to
the sociologist.

In thinking of the unity of the individual organism
—which remains in great measure an enigma to
Biology—we have to distinguish (a) the physical unity,
which rests on the fact that all the component units
are closely akin, being lineal descendants of the
fertilised ovum, and on the fact that they are subtly
connected with each other in mutual dependence and
co-operation, whether by intercellular bridges, or by
the commonalty established by the vascular and
nervous systems ; and (£) the correlated^jyr&aa?/ unity,
the esprit de corps, which in a manner inconceivable to
us makes the whole body one. That there are organ-
isms, like sponges, in which the psychical unity is
quite unverifiable is probably only a passing difficulty,
greatly lessened by our increasing knowledge of the
Me of the simplest unicellular organisms whose
behaviour is now seen to include trial by error and
other traits which we cannot interpret without using
psychical terms.

The same is true in regard to the social organism;
we have here to distinguish (a) the physical unity which
rests on hereditary kinship and on similar environ-
mental conditions, and (£) the psychical unity, the " social
mind," developed with relation to certain ends—" a
unity which is the end of its parts." It seems
structure. nature by all others doing the like."