13- Jeffries oh the Colors of Feathers. 



All the above pigments seem to be l)leiule(l and nsed in gaudily 

 colored birds much after the manner of paints by artists. So that 

 a great variety of colors mav be produced from a few pigments 

 b\- the skilful hand of nature. 



Metallic feathers, properly speaking, are those which partake 

 of the characters shown In' the red crests of the Woodpeckers. 

 The metallic appearance is limited to the barbs, the barbules not 

 showing this peculiarity, and being quickly shed. If a feather 

 from the crest of a Woodpecker, say Piciis pubescetis. be exam- 

 ined, it will at once be noticed that the red barbs have few 

 if anv barbules, and that the barbs themselves are enlarged. 

 Such barludes as are present, are not red but black, and onl\- 

 serve to diminish the effects of the red parts. They would seem 

 accordingly to be pvoperlv classed among useless hereditary 

 organs. That the red color is due to a pigment is proved b\ 

 dissolving it out and by its persistence when examined by trans- 

 mitted light. But what causes the brilliancy which has led to 

 their being called metallic' This is due to the extreme smooth- 

 ness of the barbs, the horn-cells of which they are composed 

 being fused together and solid. Thus the unabsorbed rays of the 

 beam of light which strikes them are reflected as a whole, instead 

 of 'being sent in everv direction by the walls of the cells as in 

 most cases. The metallic feathers difler from ordinary feathers 

 in the same wav that window or glass paintings difler from ordi- 

 nary pictures. Thev simply give ott" much more light, and thus 

 produce more marked eflects on our eyes. 



The colors of metallic feathers seem to be limited to the red 

 end of the spectrum, the colors varying from yellow or orange to 

 red ; blue, green or purple feathers cr)n?,tructed on tlii -"rinciple 

 do not seem to abound. 



So far we have onlv had to deal with pigments, and all has 

 been plain sailing, but the various accidental colors shown by 

 feathers are far more ditflcult of explanation. Not only are the 

 parts extremely small, but the entire subject of accidental colors 

 as regards organic structures has been in large part dealt with 

 from a theoretical point of view. The c|uestion has not been 

 how is the feather part made, but what kinds of structures will 

 produce such color eflects. Accordingly divers opinions have 

 been expressed on the subject, the most probable of these we 

 shall now endeavor to sketch out. 



