1907. | On the Inheritance of Eye-colour in Man. 87 
Self-coloured duplex eyes vary in shade, presenting different grades of 
anterior pigmentation. In the darker brown shades the anterior pigment is 
more densely deposited than in the lighter green shades, the green effect 
being produced by a thin layer—or in some cases merely a fine irroration— 
of yellow pigment above the blue posterior layer. 
Ringed duplex eyes similarly vary in shade, presenting different grades of 
anterior pigmentation. In my experience, the distribution of anterior pigment 
is always denser immediately round the pupil, both in self-coloured and 
ringed duplex eyes. Eyes with a ring of anterior pigment round the periphery 
of the iris, but without anterior pigment round the pupil, were not found in 
my observations. 
Spotted duplex eyes also present different grades of anterior pigmentation. 
The pigmented areas also vary in size and number in different individuals 
and in the two eyes of the same individual. 
Low-grade forms of the ringed duplex pattern are apparently numerous: 
under ordinary observation these might no doubt pass as blue or grey 
simplex eyes, the small pigmented ring so blending with the dark pupil as 
to be unrecognised at a short distance. 
Sunilarly, low-grade forms of the spotted duplex pattern would also pass 
as blue or grey simplex eyes at a short distance. In both cases, however, a 
closer inspection reveals their true nature. 
In carrying out my observations, I found that about half of the eyes, 
which appeared to be simplex when viewed in the ordinary way, were really 
duplex when closely examined in a good light. 
Eyes presenting grades of anterior pigmentation so low that they can 
be mistaken for simplices have not occurred in my experience, and if such 
eyes do occur, they must be extremely rare in the population which I have 
studied. 
In duplex eyes the anterior pigment is visible soon after birth, so that 
quite young infants are included in my observations. That anterior pig- 
mentation tends to increase with age in young children is evident from the 
results of my observations during three years, though to what extent is not 
yet clear, owing to the limited period of observation. 
(2) The Simplex Type. 
To the simplex type belong the various shades of eyes with posterior 
pigment only, the anterior pigment being quite absent, as in all clear blue 
and clear grey eyes. 
The darker shades of blue are apparently due to the greater delicacy and 
transparency of the fibrous tissues of the iris through which the posterior 
VOL. LXXX.—B, H 
