XII THE COLOURS OF BIRDS 255 



red feathers of the male king paradise bird {Cicin- 

 nurus regius) owe their brilliancy. This pigment, 

 called zoorubin by Krukenberg, occurs freely in 

 various species of the birds of paradise, chiefly in 

 the males, and has also been found in one of the 

 Indian trogons {Pyrotrogon diardi) in the male, 

 in the great bustard {Otis tarda), and in certain 

 varieties of the common fowl. 



Zoorubin is soluble only in dilute caustic soda, 

 from which it is precipitated by the addition of 

 acid as a dull brownish mass. Its solutions show 

 no bands, but give two well-marked reactions. If 

 cold concentrated sulphuric acid be poured cautiously 

 into a test tube containing the solution, a blue or 

 green ring forms at the junction of the liquids. 

 Again, if the solution be rendered feebly acid and a 

 trace of copper sulphate added, a bright cherry-red 

 colour is produced. The pigment does not appear 

 to contain. iron or copper. 



This list almost exhausts the known pigments of 

 birds, and its two most striking features are, on the 

 one hand, its uniformity, and on the other, the occur- 

 rence of peculiar and rare pigments like turacin in 

 exceptional cases. It may, of course, be suggested 

 that the impression of general uniformity is due 

 to ignorance, and that many families of birds may 

 contain peculiar and as yet undescribed pigments. 

 There is, of course, no proof that this is not so, but 

 at the same time the observations which have been 

 made by Krukenberg and others tend to prove at 

 least the very wide distribution of lipochromes and 

 melanins, while they have failed to disclose any pig- 

 ments of the uric acid group. The presence of 



