276 COLOUR IN NATURE chap. 



Structure of Metallic Feathers. — The brilliant 

 metallic feathers of the head region of many male 

 humming-birds are in several respects very peculiarly 

 modified. They are very short, much rounded, and 

 overlap one another ; the surface is strongly metallic 

 and marked with deep ridges (see Fig. 3). A further 

 point of interest is that the barbs, quite devoid of 

 barbules, are prolonged as a delicate fringe beyond the 

 apex of the feather. While for further details I must 

 refer to my paper on the subject, we may simply notice 

 that the metallic colouring is here not produced by a 

 modification of the distal portion of the barbules, but 

 by a deeper pigmentation and a structural change in 

 the proximal region. The result of this is that the 

 metallic colour in humming-birds tends to appear 

 first in the middle region of the body feathers — that 

 is, the region where the barbules tend to attain their 

 maximum development, and not at the tip of the 

 feathers as in sun-birds. This primitive condition is 

 well seen in the breast feathers of the female of 

 Eustephanus fernandensis, and of both male and 

 female of E. galeritus. Here we have white or dull- 

 coloured feathers, with a central spot deeply pig- 

 mented, and displaying a varying amount of metallic 

 colour. The increasing specialisation of the metallic 

 region is accompanied by a gradual retrogression of 

 the apical region which is eventually represented 

 only by the slender naked barbs. 



The metallic modification of the feathers in 

 humming-birds is therefore not accompanied by 

 any change which affects the locking together of 

 the barbules, and so the adaptability for purposes 

 of flight ; it differs in this respect sharply from the 



