560 THE DESCENT OF MAN. 



beak and round the eyes is likewise often brilliantly colored; 

 and Mr. Gould, in speaking of one species, * says that the 

 colors of the beak "are doubtless in the finest and most 

 brilliant state during the time of pairing." There is no 

 greater improbability that toucans should be encumbered 

 with immense beaks, though rendered as light as possible 

 by their cancellated structure, for the display of fine 

 colors (an object falsely appearing to us unimportant), 

 than that the male Argus pheasant and some other birds 

 should be encumbered with plumes so long as to impede 

 their flight. 



in the same manner, as the males alone of various species 

 are black, the females being dull-colored; so in a few cases 

 the males alone are either wholly or partially white, as with 

 the several bell-birds of South America (Chasmorhynchus), 

 the Antarctic goose (Bernicla antarctica), the silver pheas- 

 ant, etc., while the females are brown or obscurely mottled. 

 Therefore, on the same principle as before, it is probable 

 that both sexes of many birds, such as white cockatoos, 

 several egrets with their beautiful plumes, certain ibises, 

 gulls, terns, etc., have acquired their more or less com- 

 pletely white plumage through sexual selection. In some 

 of these cases the plumage becomes white only at maturity. 

 This is the case with certain gannets, tropic-birds, etc., 

 and with the snow-goose (Anser kyperboreits). As the 

 latter breeds on the "barren grounds," wheti not covered 

 with snow, and as it migrates southward during the winter 

 there is no reason to suppose that its snow-white adult 

 plumage serves as a protection. In the A nastwnus oscilans 

 we have still better evidence that the white plumage is a 

 nuptial character, for it is developed only during the 



size, and still less of tlie bright, colors, of the toucan's beak. Mr. 

 Bates (" The Naturalist on the Amazons," vol. ii, 1863, p. 341) states 

 that they use their beaks for reaching fruit at the extreme tips of the 

 branches; and likewise, as stated by other authors, for extracting 

 eggs and young birds from the nests of other birds. But, as Mr. 

 Bates admits, the beak "can scarcely be considered a very perfectly 

 formed instrument for the end to which it is applied." The great 

 bulk of the beak, as shown by its breadth, depth, as well LS length, 

 is not intelligible on the view, that it serves merely as an organ of 

 prehension. Mr. Belt believes (" The Naturalist in Nicaragua," p. 

 197) that the principal use of the beak is as a defense against 

 enemies, especially to the female while nesting in a hole in a tree. 

 *Kuarnphastoscarijiatus, Gould's " Monograph of Rhamphastida?. " 



