-1907.] On the Inheritance of Eye-colour in Man. 93 
_ With regard to the heredity of the duplex and simplex types, the above 
tables show that :— 
_ (1) Simplex parents mated together give all simplex offspring. 
(2) Duplex parents mated together give either (a) all duplex offspring, or 
(6) duplex and simplex offspring in the proportion of about 3: 1. 
(3) Duplex parents mated with simplex parents give either (a) all duplex 
offspring, or (0) duplex and simplex offspring in the proportion of about 1: 1. 
It is evident, therefore, that the simplex type, in heredity, behaves as a 
Mendelian recessive to the duplex type, which is dominant. We have already 
seen that the duplex type differs from the simplex type by the presence of 
anterior pigment in the iris. 
The unit-characters concerned in the heredity of the duplex and simplex 
types of eyes are, therefore, presence (duplex) and absence (simplex) of 
anterior pigment in the iris, presence being dominant over absence, which is 
recessive, 
The duplex parents in Tables II (0) and III (0) are all obviously 
heterozygous, carrying the simplex character in a recessive state. 
The duplex parents in Tables II (a) and III (a) may be either homozygous 
or heterozygous. 
The duplex parents in Table ITI (a) with large families are almost certainly 
homozygous, but in those with small families the numbers of offspring are 
insufficient to test adequately the gametic constitution of the duplex parents. 
Similarly in the case of the large families in Table II (a), one of the duplex 
parents is almost certainly homozygous, while the other parent may be either 
homozygous or heterozygous. | 
In the small families the numbers of offspring are again too small to test 
adequately the gametic constitution of the duplex parents. 
In proof of this we have the fact that in Table III (a) each of the three 
duplex parents of families 53 D. A.,125 E. R., and 209 J. H. is known to have a 
simplex parent and consequently must be heterozygous, though none of them 
has yet produced simplex offspring. Similarly in Table II (a) both duplex 
parents of family 13 J. C. are known to have a simplex parent, though they 
have not yet produced any simplex offspring. As might be expected in a 
mixed population, some of the simplex parents observed are known to have 
been extracted from a duplex parent, or to have had duplex brethren. 
For instance, in Table I, at least one of the simplex parents of families 
15 A. F.,97 H.C., 231 W.K., 255 J. H., and 257 J. C. is known to have a duplex 
parent, while of the families 31 D. N. and 243 J. F. one parent at least has 
duplex brethren. 
In accordance with the Mendelian principles, the extracted simplex type 
