PHYSICAL CHARACTERS IN MAN 49 



from very light to very dark blue, and so through 

 greenish or yellowish shades (due to a small amount 

 of brown pigment) to pale brown, dark brown being 

 rare. Every grade of colour appeared to be repre- 

 sented, with a great predominance of the paler shades. 



Sedgwick (1861) describes an interesting family in 

 County Wexford, Ireland, with tortoiseshell-coloured 

 eyes. The third generation, numbering sixteen sons 

 and five daughters, all had the peculiarity, which they 

 inherited from their mother. The mother had three 

 sisters and a brother with the same colour of eyes, 

 which was in turn inherited from their mother. Hence 

 the character was a simple Mendelian dominant. 



Bond (191 2) has studied the inheritance of the con- 



• ^ D 



i 4 4 4 4xD 



I I 



/6 Sons 5 Dau. 



Fig. 9. ^TORTOISESHELL-COLOURED EyES. 



dition known as heterochromidia iridis, in which the 

 two eyes are of different colour. In addition to the 

 patterns recognised by Hurst, he distinguishes between 

 self colour and the ray pattern, in which only one or 

 more sections of the iris are pigmented. This con- 

 dition is a fairly frequent one, and shows inheritance, 

 though the position of the ra}^ or sector is variable 

 from one generation to another. Bond finds that the 

 two eyes are unlike in pigmentation in perhaps one or 

 two individuals per 1,000. In rabbits the condition is 

 much more common, sometimes four in 100. Horses 

 with a '' wall " eye are, of course, well known, and in 

 various breeds of dogs, such as Great Danes, English 

 collies, and Old English sheep dogs, the condition is 

 not uncommon. In both horses and dogs it is fre- 



4 



