470 Proceedings of the Royal Society of Edinburgh. [Sess. 
The ratios of mixed eyes to dark eyes in each class of hair are therefore 
or 
or 
2 ac 2ad + 2 be 2 hd 
o 5 
2 cd 
d? 
2 \ + — — 
ad ’ ad ’ 
cancelling and multiplying by - } 
2R, R + l, 2. 
This ratio is evidently independent of the relative proportions of the 
different elements of the population. If R = 9, which is the value it ap- 
proximates to in the majority of cases, this ratio becomes 9:5:1. Nine 
districts in Scotland have values of R approximating to 9 ; they range from 
8’2 to 9'9. The relative proportions of mixed and of dark eyes are given 
in the following table : — 
Table VI — Percentage Mixed and Dark Eyes associated with 
each Class of Hair. 
Light Hair. 
Dark Hair. 
Black Hair. 
Eyes. 
Mixed. 
Dark. 
Mixed. 
Dark. 
Mixed. 
Dark. 
Selected districts 
67 
6-7 
7 3 
11*5 
•74 
344 
All districts .... 
6-9 
6*3 
6-3 
12-6 
•82 
2-56 
It is a matter of observation that many mixed eyes are classed as dark, 
and it seems reasonable to suppose that a fixed proportion are so classed ; 
but the figures given by the selected districts cannot be adapted to the 
ratios given above by transferring the same proportion from each group of 
mixed eyes to the corresponding group of dark eyes which we have shown 
takes place. The numbers, however, in the last group, that of black hair, 
are small, and the error of the ratio, which is approximately 1 in 4, 
may be large. 
The second group of ratios — i.e. that for the whole twenty-seven groups — 
is more nearly in accord with the supposition that a fixed proportion of the 
mixed eyes are called dark; but it would seem probable that with each 
change of the constitution of the gamete as regards hair colour a mixed 
eye tends to assume a darker hue to the casual observer, though it may 
well be that this is due as much to the colour of the eyelashes as of the 
eye itself. In fact, the difference to be explained is not so great but that 
it might be accounted for on this supposition. 
