hood. The majority are somewhere in possession
of territories, and not a few are paired. Between the territories and
the feeding ground a highway is formed by individuals passing to and
fro. Sometimes both members of the pair leave together in order to seek
food, at other times they separate and the male may be in his territory
whilst the female is with the flock. Apart from occasional
manifestations of sexual emotion on the part of a male, there is nothing
to disturb the harmony of the flock nor anything in the behaviour of the
birds which would lead one to suspect that, when they return, their
nature will change and that they will be no longer sociable; and, which
is still more remarkable, no matter how great the provocation which an
individual, when in company with the flock, may be called upon to
endure, its customary hostile response will fail to be elicited. An
incident which happened in the spring of 1917 will serve to make this
clear. A flock of some thirty Yellow Buntings, Greenfinches, and
Chaffinches were feeding in one corner of a field which had recently
been sown with barley. As they sought their food they wandered outwards
into the middle of the field, and in so doing, passed across the
territory of a Skylark. Whereupon the Skylark became excited, uttered
its call-note rapidly, and rising a few feet from the ground, attacked
those members of the flock that were nearest, which happened to be the
Yellow Buntings; and so determined were its onslaughts that the Yellow
Buntings were forced to retire. The Skylark showed no discrimination as
to sex, but attacked both males and females, and within a few minutes
succeeded in driving away at least two pairs. One would have expected
that the Yellow Buntings would have made some show of resistance; one
would have thought that the fact of being violently attacked would have
supplied a stimulus sufficiently strong to evoke a corresponding hostile
response: yet there was no mistaking the lack of interest that they
displayed in the contest--they made no effort to retaliate but seemed to
accept the situation as unalterable and left.

So far we have examined only those cases in which the pugnacious
instinct was stimulated in one of the adversaries, and in which
consequently the fighting seldom reached any high degree of severity. We
must now consider some others in which each of the opponents acts as a
stimulus to the pugnacious instinct of the other. It is here, of course,