in reaching the breeding grounds, and, in resident species, that they desert the females and retire alone to their prospective territories, so that there is a difference in the behaviour of the sexes at the very commencement of the sexual process. What is the immediate consequence? Since the male isolates itself, it follows, if the union of the sexes is to be effected, that the discovery of a mate must rest largely with the female. This of course reverses the accepted course of procedure. But after all, what reason is there to suppose that the male seeks the female, or that a mutual search takes place; what reason to think that this part of the process is subject to no control except such as may be supplied by the laws of chance?
Now, clearly, much will depend upon the rapidity with which the female can discover a male fit to breed; for if the course of reproduction is to flow smoothly, there must be neither undue delay nor waste of energy incurred in the search—some guidance is therefore necessary, some control in her external environment. Here the song, or the mechanically produced sound, comes into play, and assists in the attainment of this end. Nevertheless if every male were to make use of its powers whether it were in occupation of a territory or not, if the wandering individual had an equal chance of attracting a mate, then it would be idle to attempt to establish any relation between "song" on the one hand, and "territory" on
