To give one instance of what is called nuptial display in birds—for it will serve to illustrate what Darwin supposes to take place with some insects also, as well as forming a basis of comparison with what has been more carefully observed in the case of spiders—Belt in his often quoted work gives us the following pretty picture of humming-bird courtship. Speaking of a beautiful blue, green, and white species (_Florisuga mellivora_), he says: “I have seen the female sitting quietly on a branch, and two males displaying their charms in front of her. One would shoot up like a rocket, then suddenly expanding the snow-white tail like an inverted parachute, slowly descend in front of her, turning round gradually to show off both back and front. The effect was heightened by the wings being invisible from a distance of a few yards, both from their great velocity of movement and from not having the metallic lustre of the rest of the body. The expanded white tail covered more space than all the rest of the bird, and was evidently the grand feature in the performance. Whilst one was descending, the other would shoot up and come slowly down expanded. The entertainment would end in a fight between the two performers; but whether the most beautiful or the most pugnacious was the accepted suitor I know not.”[119] Here the display, as well as the intention, seems evident enough, and it is not a whit more so than in hundreds of other cases collected by Darwin during his lifetime, and which have been largely added to since his death. As the hen is constantly present during these performances, and as she has been known on various occasions to show a strong partiality, or the reverse, to this or that male bird, we have here a solid basis of observed fact on which to raise an hypothesis. On what facts the counter one rests, as propounded by Dr. Wallace, viz. that colour and antics are produced by superior vigour resident in the male, it is less easy to see, unless, indeed, such as point in a quite opposite direction may, on a sort of _lucus a non lucendo_ principle, be held to support it. If this be conceded, then, indeed, we have a plentiful crop, nor need we any longer feel sceptical because the eagle, say—that bird of fierce energy—does not flash out like all the crown jewels together as it descends on its prey, or because the swift, whose vital force is, perhaps, even greater, leaves no train of jewelled light to die all day, behind it, on the air. Nor need we wonder that the trogons, though as resplendent as the swifts, swallows[120] and eagles are dull-coloured, should be as lazy and sluggish as these are energetic: nor that, whereas the females of some humming-birds are sober-suited, those of others, though their vigour would seem to be in no way superior, are as gem-like as their mates: or that the males as well as the females of some wholly dull-coloured ones, and of many other plain birds, seem bursting with vigour, and indulge in all sorts of