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 of different pairs, we shall find that pairing is seldom followed by an immediate attempt to build; that an interval of inactivity is the rule rather than the exception, and that this interval varies in different species, in different individuals, and in different seasons. Our imaginary male and female will therefore be faced with considerable difficulty; for with nothing in the external environment to attract them and with no restriction imposed upon the direction or extent of their flight, their union will continue to be, as it began by being, fortuitous. Next, let us consider their position were a disposition to establish a territory to form part of the inherited nature of the male. Each one will then be free to seek food when and where it wills and to associate with other individuals without the risk of permanent separation from its mate; and, no matter how long an interval may elapse between mating and nest-building, each one will be in a position to find the other when the appropriate moment for doing so arrives. Hence, while preserving freedom of movement for each individual, the territory will render their future, as a pair, secure.