Chap. XIV. VAEIABILITY. 129 



of the genus Xenorhynchus those of the male are 

 blackish-hazel, whilst those of the females are gam- 

 boge-yellow ; with many hornbills (Buceros), as I hear 

 from Mr. Blyth/^ the males have intense crimson, and 

 the females white eyes. In the Buceros hieornis, the 

 hind margin of the casque and a stripe on the crest of 

 the beak are black in the male, but not so in the female. 

 Are we to suppose that these black marks and the 

 crimson colour of the eyes have been preserved or aug- 

 mented throuo'h sexual selection in the males? This 

 is verv doubtful ; for Mr. Bartlett shewed me in tlie 

 Zoological Gardens that the inside of the mouth of this 

 Buceros is black in the male and Hesh-coloured in the 

 female ; and their external appearance or beauty would 

 not be thus affected. I observed in Chili *^ that the 

 iris in the condor, when about a year old, is dark-brown, 

 but changes at maturity into yellowish-brown in the 

 male, and into bright red in the female. The male 

 has also a small, longitudinal, leaden-coloured, fleshy 

 crest or comb. With many gallinaceous birds the 

 comb is highly ornamental, and assumes vivid colours 

 during the act of courtship ; but what are we to think 

 of the dull-coloured comb of the condor, which does 

 not appear to us in the least ornamental ? The same 

 question may be asked in regard to various other 

 characters, such as the knob on the base of the beak of 

 the Chiuese goose (A^iser ci/gnoides), which is much 

 larger in the male than in the female. No certain 

 answer can be given to these questions ; but we ought 

 to be cautious in assuming that knobs and various 

 fleshy appendages cannot be attractive to tlie female, 

 when we remember that with savage races of man 



■^2 See also Jerdon, 'Birds of India,' vol. i. p. 243-245. 

 « 'Zoology of the Voyage of H.M.S. Beagle,' 1841, p. G. 



VOL. II. K 



