outskirts of the territory it was invading, and used them as a base from which it made repeated efforts to enter the ground of its rival. These efforts were time after time frustrated. No sooner did it leave its base than it was seen and intercepted, or else attacked; and no matter from which direction it attempted to effect an entrance, its efforts, for a time, were all to no purpose. The fighting was of a determined character, and after each attack the owner of the territory showed signs of great excitement, and, sitting upright upon a branch, spread and waved its wings, which is the specific emotional manifestation during the period of sexual activity. Eventually the intruding male succeeded by persistent effort in appropriating part of the occupied ground.
Thus we can actually witness the efforts of the individual to isolate itself from members of its own kind, and can observe the immediate consequences that follow from success or from failure. And from these consequences we can infer that, within a certain range but in accordance with the relative abundance of the species that dwell in it, every corner of the available breeding ground will be explored and every situation that evokes the appropriate response will be occupied. Moreover, since the annual dispersion is not merely a repetition in this season of that which occurred in a previous one, a progressive increase in the area occupied will follow. Yet, if the majority of species desert their breeding ground so soon as reproduction is
