272 
Notes on the Pigmentation of the Human Iris 
remarkable in that he quotes the investigations of Davenport as leading to 
Mendelism in human eye colour, and thus as confirming his own work. Now 
Davenport collected his data in precisely the same way as Galton did, i.e. by 
aid of schedules with verbal definitions of eye colour and categories practically 
identical with Galton's scheme, and therefore, according to Hurst, leading to a 
wrongful classification of 50 °/ G of the "clear" or pure blue eyes, i.e. eyes without 
anterior pigment. Yet Davenport — precisely like Hurst — finds his Mendelian 
quarter. It is thus fairly obvious that if both these authors are right and that if 
their papers actually confirm each other it must be practically of no importance 
where the limit is drawn between a "simplex" and a "duplex" eye, — for two 
different methods of observation which ought to lead to widely different numerical 
results are appealed to by both observers as confirming each the other's woi'k ! 
During my search for pure blue parentages, I made the following note on 
February 22nd, 1910, "Very many blue eyes have a slight yellowish staining, 
sometimes arranged as a pupillary ring, at other times as a faint wash here and 
there preferably following the lines of the reticulations. This staining is usually 
visible only in bright daylight with focal illumination, and not in gaslight." To 
this, I have now to add the observation that if, after deciding that a blue eye has 
no anterior pigment, such an eye be rotated upwards, so that an oblique view of 
the iris surface with foreshortened pupil is obtained, a yellow sheen of anterior 
pigmentation will often be seen. 
These observations account for the fact that I have not, as yet, met with 
a family from a pure blue or grey, or blue and grey parentage of sufficient size to 
be of any value to record. Even although many such pure blue or grey-eyed 
families were obtained, however, I question whether this would indicate any 
Mendelian inheritance with regard to iris pigmentation : the nearest approach 
I have been able to make is represented by the following pedigrees, which show 
some interesting points in inheritance of iris colour. On looking over the notes 
made when the various individuals of these and other families were examined, 
I am impressed with the frequency with which presence of the yellow staining 
of blue and grey eyes is mentioned as occurring in the upper parts of the irides. 
In light brown irides also, the upper parts of the irides are often darker brown 
{vide F. family, II. 3). I would suggest as an explanation of this interesting 
fact that the upper lid prevents the pigment from being bleached as quickly as in 
other unprotected parts. This would agree with the microscopic appearances of 
the sections given in this paper, which show the gradual disintegration of the 
pigment cells towards the anterior part of the iris. 
It is probable that the greatest incidence of light takes place at the most 
prominent or convex part of the iris surface, at a little distance from the slightly 
funnel-shaped pupil. Hence the greatest pigment activity is seen there in the 
sections, and hence the frequency of the ringed pupillary type of pigmentation in 
light eyes, and the tendency to have darker pupillary rings in dark eyes. 
