[Illustration: Fig. 44. Primary wing-feather of a Humming-bird, the _Selasphorus platycercus_ (from a sketch by Mr. Salvin). Upper figure, that of male; lower figure, corresponding feather of female.] Lastly, in several species of a sub-genus of Pipra or Manakin, the males have their _secondary_ wing-feathers modified, as described by Mr. Sclater, in a still more remarkable manner. In the brilliantly-coloured _P. deliciosa_ the first three secondaries are thick-stemmed and curved towards the body; in the fourth and fifth (fig. 45, _a_) the change is greater; and in the sixth and seventh (_b_, _c_) the shaft “is thickened to an extraordinary degree, forming a solid horny lump.” The barbs also are greatly changed in shape, in comparison with the corresponding feathers (_d_, _e_, _f_) in the female. Even the bones of the wing which support these singular feathers in the male are said by Mr. Fraser to be much thickened. These little birds make an extraordinary noise, the first “sharp note being not unlike the crack of a whip.”[114] [Illustration: Fig. 45. Secondary wing-feathers of _Pipra deliciosa_(from Mr. Sclater, in Proc, Zool. Soc. 1860). The three upper feathers, _a_, _b_, _c_, from the male; the three lower corresponding feathers, _d_, _e_, _f_, from the female. _a._ and _d._ Fifth secondary wing-feather of male and female, upper surface. _b_ and _e_. Sixth secondary, upper surface. _c_ and _f_. Seventh secondary, lower surface.] The diversity of the sounds, both vocal and instrumental, made by the males of many species during the breeding-season, and the diversity of the means for producing such sounds, are highly remarkable. We thus gain a high idea of their importance for sexual purposes, and are reminded of the same conclusion with respect to insects. It is not difficult to imagine the steps by which the notes of a bird, primarily used as a mere call or for some other purpose, might have been improved into a melodious love-song. This is somewhat more difficult in the case of the modified feathers, by which the drumming, whistling, or roaring noises are produced. But we have seen that some birds during their courtship flutter, shake, or rattle their unmodified feathers together; and if the females were led to select the best performers, the males which possessed the strongest or thickest, or most attenuated feathers, situated on any part of the body, would be the most successful; and thus by slow degrees the feathers might be modified to almost any extent. The females, of course, would not notice each slight successive alteration in shape, but only the sounds thus produced. It is a curious fact that in the same class of animals, sounds so different as the drumming of the snipe’s tail, the tapping of the woodpecker’s beak, the harsh trumpet-like cry of certain water-fowl, the cooing of the turtle-dove, and the song of the nightingale, should all be pleasing to the females of the several species.