rge of the sexual
function be assured? There is, however, a system. In the first place,
there are the assembly grounds to which the birds repair season after
season; and then, on the assembly grounds, there are the territories,
represented, as Mr. Selous tells us, by depressions where the grass by
long use has been worn away, and each depression is owned by one
particular Ruff. The assembly grounds have the effect of splitting up
and scattering the birds, and the number of Ruffs at any one particular
meeting place is limited by the territories; with the result that Ruffs
fit to breed are evenly distributed and always to be found in certain
definite places, and the Reeves know by experience where to find them.

The advantage of this territorial system is therefore apparent. Instead
of this district being overcrowded and that one deserted; instead of
there being too many of one sex here and too few of the other sex there;
instead of a high percentage of individuals failing to procreate their
kind, just because circumstances over which they have no control prevent
their discovering one another at the appropriate time--each sex has its
allotted part to play, each district has its allotted number of
inhabitants, and the waste of energy and the loss of time incurred in
the process of mating is reduced to a minimum.

Let us return again to the question of fortuitous mating, and consider
the position of a male and female that have discovered one another by
accident and have paired; what will be the subsequent course of their
behaviour? We are assuming, of course, that a territory forms no part of
their life-history. If the discharge of the sexual function takes place
immediately and the ovaries of the female are in an advanced state of
seasonal development, the construction of the nest will proceed without
delay--and the nest will answer the same purpose as the territory in so
far as it serves to restrict the movements of the birds and tends to
make them remain in, or return to, its vicinity; but if not, there will
be an interval during which both sexes will continue to wander as
before, guided only by the scarcity or abundance of food. In the first
case, there will be the attraction of the nest to prevent any untimely
separation; in the second, there will be nothing in the external
environment to induce them to remain in any particular spot. Now if we
turn to any common species and observe the sequence of events in the
life o