for they appropriate a little territory to themselves, into which they will return and stand, however much they may fly abroad. And here the birds return, in my experience, spring-time after spring-time, so that I judge them to pair for life.
Now I submit that these curious actions of the Peewit during the breeding-time do support that theory of the origin of nestbuilding which I have here roughly sketched—if not entirely, at least to a certain extent. They point in that direction. Here we have movements on the part of both the sexes, which are obviously of a sexual nature, and as to which the word "ecstatic" seems hardly to be misapplied. They are most marked (and only or most generally then dualistic) immediately after the actual pairing, and just where this has taken place they commence in the curious little run and set attitude of the male. Out of and as a result of these movements, a depression in the ground greatly resembling, if not quite similar to, that in which the eggs are laid is evolved, and into or about this is shown a tendency to collect sticks, grass, or other loose substances. How different are these collecting movements to those which we see in a bird whose nest-building instinct has become more highly developed! They seem to be but just emerging from the region of blind forces, to be only half purposive, not yet fully guided by a distinct idea of doing something for some definite end. Yet it is just these actions which most resemble ones which seem so purposive in the ordinary building of a nest. All the others seem to me to belong to that large and important group of avine movement which may be called the sexually ecstatic or love-mad group. It may, indeed, be said that, as the Peewit could not have devised a more effective way of producing a cup-shaped hollow in the ground for its eggs than by rolling or pressing upon it as it does, therefore the intention of producing it is to be deduced from the act itself, and we have no right to read any other motive force into it than this. But (besides that this view bows out instinct) the motion by which such hollow is produced cannot at all be separated from that most pronounced, peculiar, and, as it seems to me, purely sexual one of the tail, or, rather, of the anal parts, and there is, moreover, the very marked and peculiar run with the set, rigid attitude (that salient feature of a bird's nuptial
