THE COLOUR OF THE KINGFISHER. 463 



the Kingfishers very well, and William Macgillivray, who was 

 the possessor of an extraordinarily sagacious eye, both describe 

 the plumage of Alcedo ispida in a manner that is not precise. 



What is the true colour of the Kingfisher ? One is almost 

 safe in saying it has none at all, for the blue parts of the feathers 

 are colourless and transparent. Blue pigment has not been 

 discovered in any bird, and green only in the small group of the 

 Musophagidce. Very few naturalists have investigated the nature 

 of these unpigmented brilliant feathers. Professor Victor Fatio 

 appears to have been the first, and his paper and plates (Mem. 

 Soc. Phys. Hist. Nat., Geneve, xviii. 1866) are very good. Yet 

 he has one or two errors, and while describing the structure of 

 the feathers (chiefly in the Indian Blue-bird, Irena puella), he 

 offers no explanation of the cause of their blue colour. Some 

 sixteen years later Dr. Hans Gadow examined the feathers of a 

 number of birds, and described (P. Z. S. 1882) the blue ones 

 of an Ant Thrush [Pitta moluccensis = P. cyanoptera). After 

 noticing a series of ridges in the feathers of both Pitta and 

 Ccereba, he suggested the theory of " Gitterfarben," or grating 

 colours, to explain the blue of feathers. It may be stated at 

 once that such ridges do not occur in the Kingfisher, although 

 they are said to do so in other birds. Dr. Gadow was mistaken 

 in saying that by transmitted light a blue feather is always the 

 colour of its pigment ; and there are one or two other points of 

 error, such as stating that the colour is the combination of 

 structure and pigment (which does not hold good for the King- 

 fisher), and in stating that the structural layer always overlies 

 the pigment acting in combination with it (cf. also Newton's 

 'Dictionary of Birds,' p. 96). 



Further consideration of the matter may therefore be advis- 

 able ; but the difficulties attending the study of the minute 

 structure of feathers are so many that I have had to confine my 

 chief attention to the Kingfisher, and therefore I cannot speak 

 definitely of many other birds. The following remarks apply, 

 except where the contrary is expressly stated, to the blue 

 feathers from the back of the common British Kingfisher. 



I trust that the accompanying diagram will save me some 

 verbal explanation. It figures, partly in section, a small portion 

 of a single barb or ramus. The ventral or lower surface consists 



