376 Eo. ALLEN: 
gated in this country by Hurst and in America by Davenport. Hurst 
examined the eyes of children in a Leicestershire village, and also the eyes 
of their parents and grandparents, where that was possible. 
The iris, the part of the eye in which the colour is situated, owes its 
colour to two separate layers of pigment, a deep-seated layer which gives 
the effect of blue, and a layer near the surface which contains yellow and 
brown pigment. When the brown pigment of the surface layer is fully 
developed it hides completely the blue underneath it, and the eyes are 
dark brown in colour. If the brown pigment is entirely absent we get the 
true blue eye, and such an eye Hurst calls simpler. Eyes with both blue 
and brown pigment he calls duplex, and these duplex eyes are of two 
EYE COLOUR ., 
SIMPLEX 
RECESSIVES 
DIAGRAM 10. 
kinds. First, those in which the brown completely covers the iris and 
hides the blue, the so-called self-coloured or whole-coloured eye, and 
second, eyes in which the brown pigment forms a ring round the black 
pupil in the centre of the eye, whilst the greater part of the blue layer can 
still be seen. Such duplex eyes are called “ ringed.” The details of dis- 
tribution of eye-colour in two of the families examined by Hurst are 
shown in Diagram 10. 
These and other results which were obtained showed that whole-coloured 
brown eves were always dominant to ringed and also to blue. Ringed 
eves were also dominant to blue. The blue simplex eyes were pure reces- 
