298 THE STRUCTURE AND LIFE OF BIRDS cwap. 
(1.) Objective Colours. 
Colours due to pigment alone may be: (a) black; 
(6) brown; (¢) red; (d) yellow or greenish-yellow ; 
(e) very rarely green; in fact, only in the feathers 
of the Touracou. 
White pigment has been found in the pineal eye 
of the Lamprey and in one butterfly. But it does 
not, as far as is known, exist elsewhere in nature. 
Black, brown, and red are always due to pigment 
alone, yellow sometimes. These are occasionally 
modified by another layer of pigment overlying 
them. 
Blue and violet belong to the second division of 
objective colours; pigment and structure combine 
to produce them. Take any blue feather and hold it 
up to the light, so that the rays pass through it. It 
is no longer blue, but a dull black or gray. Hammer 
it, and all the blue vanishes. Green, except in the 
one case mentioned, is also a pigment-structural 
colour. Hammer a green feather from a Parrot, 
and it becomes yellow, the colour of its pigment. 
No blue pigment has been found; that which a 
blue feather contains is black-brown to yellow. The 
colour which it presents to the eye is due to the 
structure of the horny feather coating which encases 
the pigment. It has been found that under a thin 
outer sheath, there are a number of small polygonal 
cones ; from the surfaces of these cones project ex- 
tremely fine ridges, and it is believed that to these 
1 See Beddard, Anzmal Coloration, p. 4. 
