7^ Introduction: Variation. 



papillae destroyed by the beaks of antagonists: the face of the adult Rook from 

 which the feathers fall at the base of the bill as a result of dirt and wear for 

 generations; the head and face of the adult Moleo, naked owing to ages of 

 attrition from the sand in which it burrows; and so on. Examples drawn from 

 man and other animals could be given. The principle is of importance, as a 

 cause of, or directive stimulus to, variation : it should therefore not be accepted 

 without criticism. For some cases the principle of natural selection affords an 

 explanation [e. g. the remiges), but for others the argument furnished thereby 

 can hardly be made to commend itself to impartial judgment (e. g. the rectrices), 

 and for others again this principle appears to fail completely (e. g. the rackets 

 of Priuiiifurus, the comb of the Cock')\ 



Effect of light. In course of time most colours in mounted specimens 

 and skins of birds fade with exposure to the light. Among Celebesian birds 

 the effect is particularly well seen in the buff of the Nutmeg Pigeons and the 

 wash of salmon-colour on the under parts of the Moleo, which soon fade in 

 ex])Osed skins, leaving the respective parts white. Nor does light seem to be 

 operative solely uj)on the dead. 



Where the wing rests upon the body. — In nearly all birds a change of colour 

 takes place on the under side of the remiges where they rest upon the body 

 with the wing closed, so that this part differs from the distal ends and more 

 external parts of these feathers. Sometimes merely a slight change of gloss is 

 seen, but all stages of difference may be found from this up to the most marked 

 contrasts. Among Celebesian birds some of the most striking examples are: the 

 Cuckoo-shrike, Grmicalus bicolor, with the remiges white below where they rest 

 upon the body, black on the other portions: the Parrots, Prionitiirus Loricubis, 

 with the remiges below verditer-blue against the body and ]>artly where they 

 cover one another, black elsewhere; the Roller, Coracias temmiiicki — remiges 

 blue against the body, black changing with the light to bronze on the free 

 parts^); the Flycatcher, Zeocephus, with the said parts ferruginous and blackish 

 respectively; and so on. A tendency to blackness is generally seen on the distal 

 ends and external portions of these feathers. 



Where the tail-feathers are concealed by the up])er tail-coverts. — A change 

 of colour in the shafts and webs of the rectrices is generally seen on their con- 

 cealed bases, very commonly a tendency to paleness or white, suggesting a loss 

 of pigment. The most striking examples occurring in Celebes are the Cuckoo- 

 shrike. Graucalus bicolor; the two 'Nutmeg, Figeons, 3fyristicivora bicolor and hictuosa; 

 the Pratincole, Glareola isabella (as also G. orientalis). In these birds all that 

 part of the tail which is concealed by the upper tail-coverts is white, and all 



'; As shown by Stolzmann P. Z. S. 1885. 430) this may bring disaster to the -wearer of it, but the 

 author attempts to e.xplain this by natural selection. 



2) On the upper surface of the remiges these colours are reversed, being blue above where they are 

 bronze below, and bronze above where they are blue below, but tlie lines of demarcation do not exactly coincide. 



