490 THE DESCENT OF MAN 



cercus, when . adult, lias the first primary -wiug-Ieather 

 (Fig. 44) thus excised. While flying from flower to flower 

 he makes "a shrill, almost whistling noise;" " but it did 

 not appear to Mr. Salvin that the noise was intentionally 

 made. 



Lastly, in. several species of a sub-genus of Pipra or 

 Manakin, the males, as described by Mr. Sclater, have their 

 secondary wing- feathers modified in a still more remarkable 

 manner. In the brilliantly colored P. deliciosa the first 

 three secondaries are thick-stemmed and curved toward 

 the body; in the fourth and fifth (Fig. 45, a) the change 

 is greater; and in the sixth and seventh (6, c) the shaft 

 "is thickened to an e-xtraordinary degree, forming a solid, 



horny lump." The barbs also are 

 greatly changed in shape, in com- 

 parison with the corresponding f eath- 



^, ers (d, e, /) in the female. Even the 



I iii^irrr^- ijones of the wing, which support 



Fio. 44.— Primary wing-feath- . . j. T, • .1 , 



er of a Humming-bird, the se- these Singular feathers in the male, 



lasphorus platycerous (from a -Ti-ir-n , i 1 



sketch by Mr. Salvin). Upper are said by Mr. i! rascr to be much 

 ure, corresponding featiier of thickened. Thcsc little birds make 



an extraordinary noise, the first 

 "sharp note being not unlike the crack of a whip." " 



The diversity of the sounds, both vocal and instru- 

 mental, made by the males of many birds during the breed- 

 ing 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 re- 

 minded of the conclusion arrived at as 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. In 

 the case of the modified feathers, by which the drumming, 



»» Gould, "Introduction to the Trochilidse," 1861, p. 49. Salvin, "Proc. 

 Zoolog. Soc," 1861, p. 160. 



" Sclater, In "Proc. Zool. Soc," 1860, p. 90, and in "Ibis," voL iv., 1862, 

 p. 175. Also Salvin, in "Ibis," 1860, p. 31. 



