\26 The Descent of Alan. Taut II. 



for Mr. Bartlett shewed me in the Zoological Gardens that the 

 inside of the mouth of this Buceros is black in the male and 

 flesh-coloured in the female; and their external appearance or 

 beauty would not be thus affected. I observed in Chili 16 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, longitu- 

 dinal, leaden-coloured, fleshy crest or comb. The comb of many 

 gallinaceous birds 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 Chinese goose (Anser cygnoides), 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 the female, when we remember that with savage 

 races of man various hideous deformities — deep scars on the 

 face with the flesh raised into protuberances, the septum of 

 the nose pierced by sticks or bones, holes in the ears and Mps 

 stretched widely open— are all admired as ornamental. 



Whether or not unimportant differences between the sexes, 

 such as those just specified, have been preserved through sexual 

 selection, these differences, as well as all others, must primarily 

 depend on the laws of variation. On the principle of correlated 

 development, the plumage often varies on different parts of the 

 body, or over the whole body, in the same manner. We see this 

 well illustrated in certain breeds of the fowl. In all the breeds 

 the feathers on the neck and loins of the males are elongated, 

 and are called hackles ; now when both sexes acquire a top knot, 

 which is a new character in the genus, the feathers on the head 

 of the male become hackle-shaped, evidently on the principle of 

 correlation ; whilst those on the head of the female are of the 

 ordinary shape. The colour also of the hackles forming the 

 top-knot of the male, is often correlated with that of the hackles 

 on the neck and loins, as may be seen by comparing these 

 feathers in the Golden and Silver-spangled Polish, the Houdans, 

 and Creve-cceur breeds. In some natural species we may 

 observe exactly the same correlation in the colours of these same 

 feathers, as in the males of the splendid Gold and Amherst 

 pheasants. 



The structure of each individual feather generally causes anj 



4« 



Zoc'ogy of the Voyage of H. M.S. Beagle,' 1841, p. 6. 



