which is conditioned by the presence of a female, and that consequently when the male passes the boundary, the impulse to return asserts itself and the conflict ceases; or we can say that the occupation of a territory is the condition under which the pugnacious instinct is rendered susceptible to stimulation, that the stimulus is supplied by the intruder, and that when the male passes outside the accustomed area its instinct is no longer so susceptible and it therefore retires from the conflict.
Of these explanations, the first is not altogether satisfactory. It requires the presence of a female and, as we have seen, a female is by no means always present. Then it attributes to the one side of the inherited nature an influence which is not borne out by the facts, for in the ordinary routine of existence, without the incentive of battle, every individual is liable to wander occasionally beyond its boundary and to intrude temporarily upon its neighbours; and this it could scarcely do, providing its nature to remain within the territory were powerful enough to dominate its movements and curtail its activities even during the excitement of an encounter. But there is nothing inherently improbable in the alternative hypothesis, nor anything that is at all inconsistent with the behaviour as observed; on the contrary, if it is admitted, the facts become connected together and exhibit a meaning which they otherwise would not have possessed.
So much for the controlling influence of
