FEATHERS OF PEACOCK 



is as a rule the rectrices that are elongated. The plu- 

 mage of " the gaudy Indian bird " is clearly its most 

 striking peculiarity. It serves as an excellent instance 

 to illustrate the way in which the colours of birds' 

 feathers are sometimes produced. It will be noticed if 

 a peacock's feather be held out and gradually moved 

 round from one hand to the other that the shades change 

 in hue. It will be furthermore noticed, that if the 

 feather be rudely bruised the beautiful iridescent tints 

 are lost. Finally, an examination of one of the green or 

 blue feathers under the microscope shows merely a 

 dingy brownish or black coloration. The gorgeous 

 colouring disappears like that of " the purple jar." The 

 explanation of these facts is that the metallic colours of 

 the peacock's feathers are what have been termed 

 " optical " colours. They are not, that is to say, due 

 to the presence in the feather of pigments of a green or 

 blue hue, but upon a pigment of black the various 

 sculpturing of the outer part of the feather produces the 

 greens and blues, just as a slice of mother-of-pearl shows 

 different hues not present in the shell in the shape of 

 pigment. There are, of course, many colours found 

 among birds which are due to the existence in the 

 feathers of corresponding pigments. Thus the red of 

 the touracou, of which we speak on another page, is a 

 definite red pigment. Both the common peacock and a 

 variety or different species as some think it, viz. Pavo 

 nigripennis, are to be seen at the Zoo. The interest of 

 the latter bird is largely that it suddenly appeared as a 

 distinct form, and since then has " bred true." It 

 seems to be a genuine example of evolution by leaps and 

 bounds ! The pheasant tribe, to which the peacock, as 

 already stated, belongs, is an Asiatic race mainly found 

 in the tropical parts of that continent. The Argus 

 pheasant, with its enormous train of eyed feathers, is 

 perhaps the nearest ally of the peacock among the 

 Z.G, 209 p 



