XII 
THE COLOURS OF BIRDS 
257 
blue pigments usually are among animals, blue and 
green tints are exceedingly common among birds’ 
eggs, while various shades of brown, red, and yellow 
also occur. According to Professor Alfred Newton 
(.Dictionary of Birds , article “ Eggs ”), there is some 
reason to believe that for a time the eggs increase 
in brilliancy of colouring with each season until a 
maximum is reached, after which the brilliancy may 
again begin to decline. 
The pigments of the egg-shells of birds have been 
investigated by several authors. The important 
points upon which all agree are first, that the colour¬ 
ing is due to definite pigments ; and second, that 
these are derived directly or indirectly from haemo¬ 
globin—results of much theoretic importance. The 
interesting point is not that derivatives of haemoglobin 
should be used in coloration, but why, if vivid and 
beautiful colouring-matters do arise in this way, they 
should not be employed in the coloration of the 
feathers. It seems also generally admitted that even 
the ingenuity of that highly esteemed person, the 
field naturalist, is unequal to the task of explaining 
the colours of all birds’ eggs upon the hypothesis of 
usefulness, so that from the theoretical point of view 
these pigments are of quite special interest. 
Of pigments colouring eggs, Mr. H. C. Sorby 
describes seven with the following names and pro¬ 
perties :— 
Oorhodeine — a red-brown pigment of very common 
occurrence and great permanence. 
(blue pigments probably closely related, 
of which the second only yields a 
[ banded spectrum. 
Oocyan 
Banded oocyan 
