469 
1911-12.] On Inheritance of Hair and Eye Colour. 
it that R % 9, and that if it differs much from that, it is in excess rather 
than in defect. 
As the result of these calculations it is seen that if we take collectively 
all those with light eyes and distribute them according to the colour of the 
hair, the number of those with dark hair is always equal to twice the 
product of the square roots of the numbers of those possessing light hair 
Table V., showing the Values of R in several Large Towns 
and Districts. 
Reference to 
Races of Britain. 
Place. 
Number of 
Observations. 
R. 
Page 162 
Manchester 
475 
9 
„ 179 
St Austell 
850 
8*6 
„ 180 
Truro 
500 
10-3 
„ 183 
Gloucester 
500 
10 
„ 177 
Chippenham 
650 
6-8 
„ 163 
Bradford 
1400 
8-4 
„ 199 
Bourges 
420 
108 
„ 212 
Vienna 
1700 
10*8 
and black hair. The proportions in which the eyes are divided among the 
different types of hair show also that something mathematically equivalent 
to coupling takes place with apparent uniformity. This is the Mendelian 
law, and the evidence seems to me sufficient to prove that something at 
least analogous to segregation takes place. Whether the actual mechanism 
is Mendelian or not, it is evident that any other theory which seeks support 
must lead to the same numerical relationship. 
We now come to the discussion of mixed and dark eyes. Light eyes 
have been shown to fulfil the necessary conditions for Mendelian inherit- 
ance, but the other groups evidently have some different significance. This 
is best understood by referring again to Expression (1), or 
bb 
bb 1 
bb 
a 2 
BE 
2 ab 
BD 
b 2 
DD 
bd 
bd 
bd 
'2ac 
(2ad + lbc) 
2 bd 
BB 
BD 
DD 
dd 
dd 
c 2 
'led 
dd | 
d 
BB 
BD j 
DD 
which is stable if R = ^— . 
be 
