470 THE ZOOLOGIST. 



to striae acting as diffraction gratings — which would, of course, 

 only display colour in fixed directions of light ; nor is the colour 

 due to tiny prisms, nor to thin plates. I trust that I have 

 succeeded in showing that it is due entirely to the effect of light 

 reflected from a vast number of tiny projections on the surface 

 of the wall of a special cell, and is quite independent of any 

 pigment. 



All that remains now is to return to the first question of the 

 varying colours of the plumage of the Kingfisher. When we see 

 only reflected light, the feathers are pure blue ; but when a large 

 part of the light is reflected from the back of the barb, and of 

 course transmitted through the cap of the cell as orange, this 

 colour turns the blue into a dusky green, and in certain aspects 

 it may even be the only light striking the eye, so that the 

 feathers appear straw-coloured. It frequently happens that a 

 Kingfisher is more brilliant by artificial light than it is by day- 

 light — a curious state of affairs. The explanation is very simple. 

 The light is so weak that only a small proportion is sent back 

 through the cell-caps as orange light, and so we get the blue 

 colour unmixed and brilliant. In brilliant old male birds very 

 little transmitted light penetrates the caps, and so the blue is 

 purer than it is in immature or female Kingfishers. 



