88 Mr. C. C. Hurst. [May 7, 
pigment is seen, while the lhghter shades of blue and the coarser greys 
seem to be due to the greater coarseness and opacity of the same tissues. 
These structural differences appear to be continuous, a series of intermediate 
blue-greys linking up the finer blues with the coarser greys. 
A further complication arises from the fact that, in most cases, the finer 
tissues of the iris become coarser with age, and young children with dark 
blue eyes may mature into adults with light blue, blue-grey, or grey eyes. 
I have found striking illustrations of this in large families, where a whole 
series of shades from blue to grey were seen, the younger children being blue 
and the older ones grey. Consequently, no attempt has been made to 
distinguish between the many shades of clear blue and clear grey eyes, but all 
eyes with posterior pigment only are classed as simplex. 
Finally, the clear blue and clear grey simplex eyes, with no trace of 
anterior pigment, must be carefully distinguished from the numerous low- 
grade duplex eyes, previously noted, whith are often called “blue” or 
[oreve, 
Heredity of the Duplex and Simplex Types. 
All families with less than two children are omitted, and families of two 
were not taken freely. At first, the largest families available were selected, 
but afterwards it seemed desirable to study collaterals, consequently some 
small families are included. 
Out of the 139 families observed, 20 were simplex matings, 50 were 
duplex matings, and 69 were duplex-simplex matings. 
Simplex Matings. 
The 20 matings of simplex females with simplex males produced 
101 offspring, all of the simplex type. Table I gives the numbers found 
in each family. Each family is distinguished by the number and initials of 
the male parent :— 
