ggfi THK DKSCENT OF MAN. 



they acquire their beautiful plumes only during the breeding- 

 season. Moreover, such plumes, top-knots, &c., though possessed 

 by both sexes, are occasionally a little more developed in the 

 male than in the female; and they resemble the plumes and 

 ornaments possessed by the males alone of other birds. It is also 

 known that confinement, by affecting the reproductive system of 

 male birds, frequently checks the development of their secondary 

 sexual characters, but has no immediate influence on any other 

 characters; and I am informed by Mr. Bartlett that eight or 

 nine specimens of the Knot (Tringa canutus) retained their un- 

 adorned winter plumage in the Zoological Gardens throughout 

 the year, from whieh fact we may infer that the summer plumage 

 though common to both sexes partakes of the nature of the ex- 

 clusively 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 colors throughout 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 

 subsequently been taken advantage of in certain cases for gain- 

 ing 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 splendidly colored honey-suckers (Nectariniae) 

 of India and some sub-genera of obscurely colored pipits (Anthus) 

 have a double, whilst others have only a single annual moult."' 

 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 

 bustards and plovers the vernal moult is far from complete, some 

 feathers being renewed, and some changed in color. There is 



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

 &c., Macgillivray, 'Hist. Brit. Birds,' vol. iv. p. 371; on Glareolae, cur- 

 lews, and bustards, Jerdon, 'Birds of India,' vol. ill. pp. 615, 630, 683; 

 on Totanus, ibid. p. 700; on the plumes of herons, ibid. p. 738, and 

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

 'Ibis,' vol. V. 1S63, p. 33. 



s' 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. 32. 



