444 THE DESCENT OF MAN. 



lett that eight or nine specimens of the Knot (Tringa 

 canutus) retained their unadorned winter plumage in the 

 Zoological Gardens throughout the year, from which fact 

 we may infer that the summer plumage, though common 

 to both sexes, partakes of the nature of the exclusively 

 masculine plumage of many other birds.* 



From the foregoing facts, more especially from neither 

 sex of certain birds changing color during either annual 

 moult, or changing so slightly that the change can hardly 

 be of any service to them, and from the females of other 

 species moulting twice yet retaining the same color through- 

 out the year, we may conclude that the habit of annually 

 moulting twice has not been acquired in order that the 

 male should assume an ornamental character during the 

 breeding-season; but that the double moult, having been 

 originally acquired for some distinct purpose, has subse- 

 quently been taken advantage of in certain cases for gaining 

 a nuptial plumage. 



It appears at first sight a surprising circumstance that 

 some closely-allied species should regularly undergo a 

 double annual moult, and others only a single one. The 

 ptarmigan, for instance, moults twice or even thrice in the 

 year, and the black-cock only once; some of the splen- 

 didly colored honey-suckers (Nectariniae) of India and 

 some sub-genera of obscurely colored pipits (An thus) have 

 a double, while others have only a single annual moult, f 

 But the gradations in the manner of moulting, which 

 are known to occur with various birds, show us 

 how species or whole groups might have originally 

 acquired their double annual moult, or having once 

 gained the habit, have again lost it. With certain bus- 

 tards and plovers the vernal moult is far from complete, 

 some feathers being renewed, and some changed in 

 color. There is also reason to believe that with certain 



* In regard to the previous statements on moulting, see, on snipes, 

 etc., Macgillivray, "Hist. Brit. Birds," vol. iv, p. 371; on Glareolse, 

 curlews and bustards, Jerdon, "Birds of India," vol. iii, pp. 615, 

 630, 683; on Totanus, ibid, p. 700; on the plumes of herons, ibid, p. 

 738, and Macgillivray, vol. iv, pp. 435, 444, and Mr. Stafford Allen, 

 in the <k lbis," vol. v, 1863, p. 33. 



f On the moulting of the ptarmigan, see Gould's " Birds of Great 

 Britain." On the honey-suckers, Jerdon, "Birds of India," vol. i, 

 pp. 359, 365, 369, On the moulting of Anthus, see Blyth, in " Ibis/' 

 1867, p. 33, 



