120 On Heterochromia Iridis in Man and Animals 



The parti-coloured iris occurs during inter-breeding fairly frequently, 

 but the parti-coloured skin must be extremely rare in the human species, 

 whereas in domesticated animals the parti-coloured or " wall " eye and 

 the pied coat pattern both occur when self colour is mated with white. 

 This fact strongly suggests that the factors for self colour in the 

 negro or the factor for self white in the European, or both of them, 

 offer more resistance to disintegration than the factors which control 

 the self-duplex and the self-simplex patterns in the human eye. 



Some association no doubt does exist between skin-colour and eye- 

 colour even in the human subject; the dark brown or black iris and the 

 black skin of the negro, the blue eye, reddish hair and white skin of 

 the northern races illustrate this point. 



The same is certainly true in many wild species and domestic 

 varieties of animals, and even in extracted hybrid varieties we have the 

 association of the agouti and blue coat colour with black eyes in mice, 

 and chocolate eye pigment with pink eyes in the Himalayan rabbit, the 

 Siamese cat, and the Cinnamon canary (Bateson, p. 114) (9). 



But owing possibly to the difficulty of breaking up the self-skin 

 colour factor in man and the greater susceptibility of the self-colour 

 iris factor to disintegration, the association which originally existed 

 between these factors is partially dissolved when they are called upon 

 to behave independently under the altered conditions of inter-breeding. 



Thus in the native Irish race, dark complexion and dark hair have 

 become associated with the violet or simplex eye. It is a suggestive 

 fact that the factor for self skin colour in man which refuses to dis- 

 integrate when mated with absence of colour or white skin should 

 apparently refuse also to segregate in gametogenesis. 



Some anomalous facts about albinism in the human subject are also 

 of interest in this connection. 



A woman M. T. aet. 35, the daughter of a brown-haired, blue-eyed 

 father, and a red-haired, blue-eyed mother, and one of four children 

 (two daughters with red hair and blue eyes, and one son with dark brown 

 hair and blue eyes) was herself born with white pigmentless hair, eye- 

 brows, and eyelashes and pink pupils and pigmentless irides, in fact 

 with all the characters of the true albino. At the age of puberty the 

 hair of the head of this woman gradually assumed a red tinge and 

 is now the ordinary fiery red colour, while the eyebrows and eye 

 structures have remained free from pigment. 



In this case the association which existed in childhood between the 

 recessive characters, absence of skin and hair pigment, and absence of 



