PHYSICAL CHARACTERS IN MAN 51 



the e\^e is peculiar, its black colour being due to the 

 presence in the iris and in deeper tissues of branching 

 cells packed with dark granules. 



In the pearl or white eye of pigeons and the " daw " 

 eye, as in the Malay fowl, there is no anterior pigment 

 in the iris, but its tissues are opaque, owing to the 

 presence of crow^ded colourless granules. This ap- 

 parently corresponds with the " wall " eye in horses, 

 dogs, and pigs. The muscle fibres of the avian e3^e, 

 however, are striated or voluntary, and not plain as 

 in the mammals. Pearl eye in pigeons is recessive 

 to yellow or " gravel " eye, as " daw " e^^e in fowls 

 is to amber or black eye when the latter is due to 

 anterior pigment. The yellow eye derives its colour 

 from a network of branching cells containing yellow 

 granules. If the latter are closely packed, the eye 

 may appear black. In fowls the ^^ellow e3^e ma}' be 

 due to (i) granules in the connective tissue cells; 

 (2) granules in the striated muscle cells, as in Dorkings 

 and Orpingtons. In owls the yellow eye is due to 

 bright 3"ellow granules in cells coating the iris. 



Brown and black eyes in birds are produced b}' a 

 layer of branching cells on the iris containing dark 

 pigment granules. Ruby e3^es are produced in various 

 ways in different birds ; and some birds, such as certain 

 birds of paradise, have parti-coloured irides. Gene- 

 tically, black due to pigmented iris is dominant over 

 yellow and other grades of iris pigmentation. 



Skin Colour and Hair Characters. 



Hurst (191 2) has summarised the studies on hair 

 and skin colour in man, and added some observations 

 of his «wn. The main points with regard to hair 

 colour are: (i) That the brown shades of colour 

 appear to be continuous from white (albino) hair to 

 jet black; (2) the reds form a separate series due to a 



