C. J. Bond 79 



In the common Ring Dove {Turtur communis) the ruby colour is 

 due to the presence of" a surface layer of branching cells with yellow 

 pigment granules, which surround the capillaries on the anterior surface 

 of the iris. 



The rich ruby eye of the Victoria Crowned Pigeon {Goura victor-iae) 

 is due to the same cause. In this species also, as in the Doves, the red 

 colour is common to both sexes. In the nestling Victoria Crowned 

 Pigeon the colour of the iris is black. At the age of three months the 

 iris assumes a bright yellow colour, but I have not been able to ascertain 

 the age at which the yellow gives place to the ruby colour. 



In the Dragoon Pigeon and some other fancy breeds all grades of the 

 ruby eye occur, from bright red through dull red to orange and yellow. 

 In some birds the ruby or " red currant " colour is limited to the outer 

 zone of the iris where blood vessels abound, while the inner zone sur- 

 rounding the pupil, where there are fewer capillaries, retains the orange 

 or yellow colour. 



The Ruby eye in Doves and Pigeons loses much of its brilliant red 

 colour after death, and, as we shall see later when dealing with the 

 chemical aspect of the problem, the red and eventually the yellow colour 

 are both lost when the eye is placed in a reducing agent like formalin. 



The ruby colour is thus a superimposition effect due to the covering 

 of red blood vessels with yellow pigment cells. The exact way in which 

 the optical effect is produced is a subject for further study. 



The Ruby eye in the Cayenne Lapwing (Vanellus cayennensis) 

 presents a different problem. Here the red colour of the iris is due to 

 the actual presence of rounded, oval, or slightly branched cells packed 

 with fine granules of a reddish mauve coloured pigment. These cells 

 are situated on and among the muscle cells and the capillaries of the 

 iris. This is the only example at present found of a colour effect in the 

 iris due to the presence of pigment granules which could not be included 

 in the yellow, brown or black groups. Not only are the granules which 

 produce the red colour in the Cayenne Lapwing's iris histologically 

 different from the yellow pigment granules which form the surface layer 

 in the Dove's and Pigeon's iris, but they also differ in chemical com- 

 position. In the Lapwing the ruby colour persists after death and the 

 pigment granules retain their red colour even after a long immersion 

 in 5 °/o formalin. 



The " Parti or Zone " coloured Iris. 



In some of the Birds of Paradise, notably in Lawes' Bird of Paradise 

 {Parotia lawesi), and possibly in other species, striking colour effects are 



