124 On Heterochromia Iridis in Man and Animals 



It seems clear, from the familial distribution of these cases of 

 irregular eye colouration, that the ray eye pattern in man, like the 

 Dutch coat pattern in the rabbit, is controlled by a definite gametic 

 factor or factors. 



The duplex ray pattern like the duplex self-colour and ringed 

 patterns seems to be dominant over the simplex character (see Baines, 

 2nd family). It would also appear to be dominant over self-colour 

 duplex when the self-colour duplex is of lighter shade than the ray 

 duplex (see Frake), but this dominance only occurred in two out of nine 

 children and then only in one eye, the other being self-colour duplex. 

 In two others the self pattern was associated with irregular patches of 

 darker pigment as we shall see later. These facts suggest that ray 

 pattern is only dominant over self-colour pattern when the original 

 factor for self-colour has undergone some dilution or when disintegration 

 and dilution are operating together. 



Concerning this difference in genetic composition between self-colour 

 and Dutch pattern, Bateson says (p. 142)(9): 



" Physiologically we should I suppose refer it to differences in the 

 distribution of one of the chromogenic factors, rather than to the 

 presence or absence of an additional factor." 



It is these differences in the distribution of one or both of the 

 chromogenic factors that I wish to consider in the light of the evidence 

 derived from cases of irregular iris pigmentation in man and animals. 



It is true that there are albinos of different factorial composition in 

 every species, just as there are dominant and recessive " whites " among 

 fowls. There are some extracted albinos which carry the factor for self- 

 colour, and others which carry the factor for pattern, though both lack 

 the colour developer factor itself. 



The different results obtained in mating the black fantail cock with 

 the two white fantail hens of different gametic composition afford 

 another example of the influence of the gamete which bears the 

 recessive character on the determination of colour pattern. 



But while by the assumption of a colour factor awaiting development 

 in the albino and a developer factor in the self-coloured animal we can 

 by the mutual interaction of these factors explain the restriction of the 

 colour unit character to certain skin areas, and the dilution of colour in 

 zygotes of different gametic composition, we have not thereby explained 

 the original distribution of these different factors in either the albino 

 or the pied animal. 



Thus it appears that besides presence and absence, and besides 



