It would be foreign to the purpose of this book to pursue this theme at length. Let it suffice to say that while the "Sexual Selection" theory still holds good, it has, so to speak, changed its complexion. And this largely owing to the accumulation of new facts. For the most important of these we are indebted to the singularly exact and laborious observations analysed, clarified, and interpreted with remarkable insight and sagacity of Mr. H. Eliot Howard, one of the keenest Ornithologists of our time. He has set forth his case, and interpreted his facts with masterly skill, and there seems no escape from his conclusions. Briefly, he has shown that birds of quite sober coloration like the warblers, which formed the basis of his investigations, engage in displays quite as remarkable, and of precisely the same character as in birds of gaily coloured plumage. From this it is clear that this wing-play is not prompted by a more or less conscious desire to display conspicuously coloured patches of colour, for of colour there is none save that of the general hue of varying shades of brown, as in the case of the grasshopper warbler, for example. Nor is the display, apart from colour, to be regarded as a performance slowly perfected through long generations through the selection of females, coy and hard to please. We must regard these "Nuptial flights" and wing-displays, as the outward and visible signs of a state of ecstatic amorousness on the part of the males which, by their persistence and frequent recurrence, at last arouse sympathetic response in the females. They play the part of an aphrodisiac. Without them there would be no mating. In my "Courtship of Animals" those who will may pursue this subject further. [Illustration: _Herons_]