functions in society may, in social animals like the
ants, lead to the formation or differentiation of a third or fourth
kind of individuals. This is what is called _polymorphism_. Here it is
not the sexual function causes the correlative differences of the
individuals, but division of social labor. The ecphoria of the
hereditary mneme which produces the polymorphous, and more or less
asexual individual forms (workers, warriors,) still proceeds through
the energies of the reproducing germs. Here the action of selection is
necessary to explain the phenomena.

In man, sexual differentiation has led to the formation of two kinds
of individuals, differing little in their correlative attributes, but
each bearing one kind of germinal cells. In sexual union man plays the
active part, woman, the passive. When sexual activity, in the animal
kingdom, is no longer limited to the movement of one of the cells but
requires the displacement of the whole individual, we can quite
understand that the organization of these individuals must become much
more complex, and that it requires a central nervous system as a
directing apparatus. Sexual individuality thus involves collaboration
of the other organs of the body, and especially that of the central
organs for reflex movements, the instincts and the higher mental
faculties of man, in the accomplishment of the fecundating act those
which are the consequences of it.

From this simple animal origin is evolved the complex sexual love of
man. The duty of the active or male individual is to bring the
spermatozoa to a point where they can easily reach the female cells or
ovules. When this is done the duty of the male is accomplished. In the
passive or female individual of the higher animals, pairing and
conjugation are only the commencement of reproductive activity.
However, this is not the case in the whole animal kingdom. For
instance, fish have distinct sexes, but in them the female deposits
her non-fecundated eggs in the water and is not concerned with them
any further. The male then arrives and discharges his sperm on the
eggs. In this case fecundation takes place without copulation. With
such a system sexual love and maternal love lose their _raison
d'etre_, for the young fish are capable of providing for themselves as
soon as they are born. There are, however, a few exceptions, one of
the most curious being that of certain fish of the Dead Sea, in which
the male incubates the eggs by t