C. J. Bond 101 



made by Hurst to subdivide his duplex type into a self-coloured pattern 

 in which the pigment was spread over the whole anterior surface of the 

 iris, a ring pattern in which it was deposited in a circle round the 

 margin of the pupil, and a spotted pattern in which it was collected into 

 discrete spots or patches. Owing to lack of material and to the fact 

 that deposition of pigment tends to increase during childhood, Hurst 

 was unable to establish fully the genetic relations between these types, 

 beyond showing that the self-coloured behaved as a dominant towards 

 the ringed pattern. 



From Hurst's description it would appear that the genetic factor or 

 factors which control eye-colour in the human species (although they 

 may be classified into two or more sub-types) operate under normal 

 conditions in both eyes equally, that is to say they are bi-lateral or 

 bi-iridial in action. 



It is the object of this paper to draw attention to some examples of 

 irregular iris pigmentation in man and in some varieties of domesti- 

 cated animals and bii'ds in which this symmetrical arrangement is 

 departed from. 



It has been known for a long time that in a certain proportion of 

 cases in the human species, perhaps one or two per 1000, the two eyes 

 of the same individual are of different colours. When this condition of 

 heterochromia does occur, according to my own experience, the darker 

 or coloured eye presents some shade of the duplex type, either arranged 

 on the self-colour pattern, or more frequently affecting a larger or 

 smaller portion of the iris either in a continuous sheet or in discrete 

 sections, the remainder of the iris being blue or some lighter shade of 

 the coloured pattern. The other or lighter eye is either simplex or more 

 generally a lighter shade of the duplex pattern of the coloured eye. 



Different degrees of this condition of asymmetrical colouration are 

 met with, varying from complete heterochromia to one small sector of 

 darker colour in an otherwise duplex eye. 



In the course of the examination of the pigment distribution in a 

 considerable number of individuals an irregular type of the duplex 

 pattern will be found which does not conform to the self-coloured or 

 the ringed or the spotted pattern described by Hurst. 



In an otherwise blue or grey, i.e. a simplex eye, a portion of the iris, 

 generally embracing the whole diameter from periphery to pupillary 

 margin, and more or less triangular in shape, with its base at the 

 periphery, will show in different cases different degrees of pigmentation 

 from light yellow to dark brown. 



