126 On Heterochromia Iridis in Man and Animals 



If we imagine the factor for self-eye colour to have been built 

 up during animal evolution out of two primary factors, one for each 

 eye, and each of these again out of a number of secondary factors 

 controlling the deposit of pigment in different sectors of each iris, and 

 that all these factors have become welded together into one whole, and 

 now act as one integrated factor, then we shall associate the appearance 

 of the irregular or ray pattern with some preceding disintegrative 

 change in the factor for self-eye colour in the human species. 



Some disintegration, partial or complete, is the first step in the 

 origin of a new colour pattern. ' It provides the opportunity for the 

 re-arrangement of subordinate factors which takes place during gameto- 

 genesis and gametic union. 



From this standpoint we should regard the appearance of pied coat 

 colour and pied eye colour, or " wall " eye, in the Orkney rabbits, and 

 the appearance of the heterochromic eyes in the blue and white tumbler 

 fantail hybrid of the third generation, as the outcome of a disintegration 

 of the factors for self-coat colour or self-eye colour and this disintegration 

 appears during the mating of individuals of different genetic com- 

 position. 



The establishment of these new types on a basis of genetic stability 

 (such as we see in the ring and ray iris pattern in man, and the Dutch 

 coat pattern in rabbits) becomes then a matter of the re-welding of 

 these secondary factors into one newly integrated factor, of a fresh type, 

 and with a different arrangement of its component parts. 



Thus regarded the only way to obtain the piebald variety in the 

 human species is to disintegrate the factor for self-colour which at 

 present controls, in different degrees of dilution, the whole skin area, 

 and which at present ordinarily refuses to segregate in gameto-genesis. 



The way to bring about irregular iris colour pattern is to break 

 down (as we have done in the heterochromic pigeon) the self-colour 

 factor for both eyes into two factors controlling its different eyes, and 

 these again into subordinate factors controlling different areas in the 

 same iris. 



The inter-mating of dark duplex with light duplex and duplex with 

 simplex types results in the appearance of partial or complete hetero- 

 chromia in some cases in the human species, and the familial distribution 

 of these cases of irregular iris pigmentation suggests the possibility 

 of the establishment under certain conditions of a heterochromic variety 

 of the human race. 



Looked at from this point of view, the difference between individual 



