sexual instinct. Is, then, the male's call an indication of his readiness to yield to stimulation? Without a doubt it is an index of the general physiological state which generates the sexual impulse, without a doubt it denotes a general preparedness to breed, but there is no evidence to show that it denotes the degree of ardour of the male at any particular moment, and much that proves the contrary. So that only by the female producing some special sound which will attract the males that are eager and bring them rapidly to the spot where she happens to be, only thus is it possible to insure the consummation of the sexual act. This, it seems to me, is the purpose' of the peculiar call of the female—a call which, so far as biological interpretation is concerned, is just as much a song as the melody of the Marsh-Warbler—and its interest for us just now lies in this, that here we have a special case in which the sexes have separate territories, the female is polyandrous, and the voice of the male is not sufficient by itself to bring to pass the union of the sexes; and in which, consequently, if the purpose of song be that of recognition, we should expect to find, as we do find, that the female had a distinct and penetrating call.
We now come to the question of "warning," by no means the least important purpose of song. I pointed out that one of the chief differences between the call-notes and the song was that the former were socially serviceable,
