\9 2 



The Descent of Man. 



Part U. 



beak and round the eyes is likewise often brilliantly coloured ; 

 and Mr. Gould, in speaking of one species/ 2 says that the colours 

 of the beak " are doubtless in the finest and most brilliant state 

 " during the time of pairing.' 5 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 colours, (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-coloured ; 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 {Brrnidu autarcfica), the silver-pheasant, &c, 

 whilst 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, &c, have acquired 

 their more or less completely 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, &c, and with the snow-goose (A riser hyperbor&us). As the 

 latter breeds on the " barren grounds," when 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 Anastomus oscitans, we have still better 

 evidence that the white plumage is a nuptial character, for it is 

 developed only during the summer ; the young in their imma- 

 ture state, and the adults in their winter dress, being grey and 

 black. With many kinds of gulls (Larus), the head and neck 

 become pure white during the summer, being grey or mottled 

 during the winter and in the young state. On the other hand, 



Bates (' The Naturalist on the 

 Amazons,' vol. ii. 1863, p. 311) 

 states that they use their beaks for 

 reaching fruit at the extreme tips 

 of the branches ; and likewise, as 

 stated by other authors, for ex- 

 tracting; e£2;s and vouns birds from 

 the nests of other birds. But, as 

 Mr. Bates admits, the beak " can 

 44 scarcely bs considered a very per- 

 " fectly-formed instrument for the 

 " end to which it is applied." The 

 g?eat bulk of the beak, as shewn 



by its breadth, depth, as well as 

 length, is not intelligible on the 

 view, that it serves merely as an 

 organ of prehension. Mr. Belt 

 believes (' The Naturalist in Nica- 

 ragua,' p. 197), that the principal 

 use of the beak is as a defence 

 against enemies, especially to the 

 female whilst nesting in a hole in a 

 tree., 



52 Ramphastos carinatns, Gould's 

 ' Monograph of Ramphastidae.' 



