44 HEREDITY AND EUGENICS 



his battalions, and Catherine de Medici is said to 

 have endeavoured to produce a race of dwarfs by 

 bringing about matings between them. 



Eye Colour. 



The Mendelian studies of eye colour up to 191 2 

 were summarised by Hurst (191 2). He defined three 

 patterns of distribution in the pigmented e^^e : self, 

 where the brown is distributed all the way to the 

 periphery of the iris; ringed, in w^hich the brown is 

 confined to a ring around the iris; and spotted, in 

 which irregular spots and patches occur on a blue 

 background. The blue or grey colour represents 

 absence of brown pigment, and is simply the apparent 

 colour of the muscle fibres in the iris as seen through 

 the cornea. 



A recent paper (Boas, 1919) presents statistics 

 of e3'e colour which, it is claimed, do not support the 

 Mendelian contention that two blue-eyed individuals 

 have only blue-eyed offspring. But the wTiter admits 

 that in collecting these data, persons with a certain 

 amount of brown in their eyes may have been classed 

 as blue-e^^ed. Pearson and others have also studied 

 carefully some of the more detailed differences in eye 

 pigmentation which are important for a complete 

 anah^sis. It is clear that the conception of a single 

 Mendelian factor difference between brown and blue 

 e\^es is only a rough first approximation in the study 

 of this subject. 



Usher (1920), from a careful histological examina- 

 tion of six albino eyeballs, found traces of pigment in 

 four. The fifth was unknown, and the sixth, that of an 

 infant, was devoid of pigment. Usher therefore con- 

 cludes that total absence of pigment cannot be used 

 as a definition of albinism in man . The fovea centralis* 



* This is a pit in the middle of the macula lutea or point of 

 clearest vision at the centre of the retina. 



