previously evoked response, is there unresponsive; or again, it goes in search of food and collects with other males bent on a similar errand, and in presence of what we know would be an exciting influence under other circumstances, it nevertheless remains silent. Hence the relationship between the song and a male rival seems, as in the case of the headquarters, to depend in the first instance upon the occupation of a territory.
So that the relationship between the song and the territory as a whole is clearly of a different order from that which obtains between the song and the headquarters, or the song and a male rival; for the first, as far as can be judged by observation, is exclusive of, whilst the second and the third involve, cross-correlation. How are these facts to be explained? We have already seen that it belongs to the nature of the male during the season of reproduction to establish itself in a definite place, and this action is just as much a part of its hereditary nature as the building of the nest is of that of the female, and it is just as necessary for the successful attainment of reproduction. What exactly the stimulus is to this mode of behaviour we do not know; we can go no further back than the internal organic changes which are known to occur and which we assume, not without some reason, are responsible for its initiation. Granting, then, that there is this congenital disposition, what relation does it bear to the song? Without a doubt the song is likewise
