iV)2 The Descent of Man. 1 'art 11. 



beak and round the eyes is likewise often brilliantly coloured ; 

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

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

 " during the time of pairing." Tliere is no greater improbability 

 that toucans should be encumbered with immense beaks, though 

 rendeied as light as possible by their cancellated structure, for 

 the display of fine colours, (an object falsely appearing to up 

 unimportant), than that ihemale 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 {Bn-tdda autarclica), the silver-pheasant, &c., 

 whilst the females are brown or obscurely mottled. Therefore, 

 on the same principle as before, it is probable that both s^-xes 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 ease with certain gannets, tropic- 

 birds, &c., and with the snow-goose (.4)7 ser Tiypfrbortuii). 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 sei-ves 

 as a protection. In the Anastomun oaciUmF,, 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 nook 

 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 hy its breadth, dspth, as well as 



Amazons,' vol. ii. 1863, p. 341) length, is not intelligible on the 



states that they use their bealcs for view, that it serves merely as an 



reaching fruit at the extreme tips organ of prehension. Mr. Belt 



of the branches ; and liliewise, as believes (* The Naturalist in Nica- 



stated by other authors, for ex- ragua,* p. 197), that the principal 



fcracting eggs and young birds from use of the beak is as a defence 



the nests of other birds. But, as against enemies, especially to the 



Mr. Bates admits, the bealc " can female whilst nesting in a iiole in a 



" s(drcely be considered a very per- tree. 



" fectly-formed instrument for the ^^ Ramphastos carinatus, Gonld'i 



"end to which it is apfilied." The 'Monograph of Ramphahtidae.' 

 ([Tesi bulk of the bcalc, as shewn 



