ritories, and the Wild Duck will teach her young to seek their food.

In whatever direction we turn, we find that many breeding grounds are
subject to incessant change. Ancient haunts disappear, new ones come
into being, a change which makes life impossible for this bird, as
likely as not benefits that one, and so on. There is no stability. Hence
in any given district each recurring season there must needs be a large
number of individuals which are obliged to seek new stations, and if
there were no control over their distribution, if each one were free to
establish itself wherever it chanced to alight, this locality might be
overcrowded and that one deserted; and, bearing in mind how many species
there are that require similar conditions of existence, we can infer
that the successful attainment of reproduction would become impossible
for many of those individuals so long as each species was indifferent
to the presence of the others. On the other hand, if there were no
control over the range of the intolerance, the smaller bird would have
no chance in competition with the larger, and it is doubtful whether the
larger would gain an advantage commensurate with the energy it would
expend in ridding its area of the smaller. I have described battles in
which the opponents were only distantly related; for instance, the
Moor-Hen will attack almost any bird--Partridge, Lapwing, or
Starling--that approaches its territory even temporarily. Nevertheless
the antagonism between kindred forms is more prevalent, and, as a rule,
characterised by more persistent effort; and thus it seems as if the
susceptibility of the fighting instinct has its limitations, the degree
of the responsiveness being dependent upon the affinity of the
opponents.

Suppose now that we take an area inhabited by a number of different
species requiring like conditions of existence, divide it into three
sections, and imagine that in one they were all sociable, that in
another they were all hostile, and that in a third those which were
closely related were intolerant of one another. Let us suppose further
that each one of them was represented by the full number of individuals
that the law of territory would allow. In the first section an
individual would establish itself, and, becoming intolerant of its own
kind, would exercise dominion over an area roughly sufficient, providing
conditions were normal, to insure an adequate supply of food for its
young. But it woul