THE VERTEBRATA 157 



story, but a few words about feathers, however, 

 may find a place here. 



The colour of feathers is a subject of much 

 interest. Everyone is fam liar with the brilliant 

 tints often presented by the feathers of birds, and 

 everyone who is a close observer of natural ob- 

 jects knows that there are some feathers which 

 are iridescent, changing colour according to the 

 direction in which light falls on them. It has 

 been shown by Dr. Gadow that this variation of 

 the colour of a feather is due to its structure; 

 this may be described as prismatic, for the small 

 divisions of the feather present acute angular 

 edges, which reflect the light like the edges of 

 a prism. These are symmetrically repeated all 

 along the feathers, so as to reflect the same 

 colour throughout. Thus in the plumage of the 

 common red and green parrot, we see feathers 

 that are red when held in one position, and 

 yellow when shifted to another position ; while 

 there are also feathers that are blue when seen 

 in one position, and green when seen in another ; 

 the alternative colour being the one next in order 

 in the rainbow. 



Another point regarding the colours of feathers 

 has no doubt puzzled many of our readers; and 

 that is, the metallic quality of the colouring in 

 some exceptional feathers, and in these only. 

 The feathers of the parrot just referred to, are, 

 for instance, simply red and yellow, or blue and 

 green ; but the feathers of the peacock, though 

 displaying the same colours, show a metallic 

 lustre which is wanting in the other case. The 

 feathers of the starling, the blackbird, and the 

 black hen of the farmyard, though not so 

 brilliant as those of the peacock, are the same 



