HEREDITY IN PLANTS, ANIMALS, AND MAN. ole 
sives. and whenever father and mother both had such eyes all the children 
also had eyes of the same kind. 
The dominant self-coloured and ringed eyes, on the other hand, might 
be either pure dominants, or hybrids containing the factor for reces- 
sive blue eves. Several instances of these hybrids are seen in the 
diagram. 
The next diagram (Diagram 11), which is extracted from a much larger 
pedigree illustrated by Bateson in his book on “ Mendel’s Principles of 
Heredity,” shows a portion of the pedigree of a family living in a cluster 
i % 
n 6 Pa © 
MANS 
Wi DESCENDANTS @ @. 
(of 
IV 0@0000 oS 
\ 
MANY 
DESCENDANTS 
guided Bd oleh I22 
ie 
NIGHT BLINDNESS IN MAN. 
ALL MARRIED NORMALS 
EXCEPT O 
DIAGRAM II. 
The black dises represent the affected individuals, the rings those who did not sutter 
from the disease. In the exceptional case (black disc with white centre) both parents were 
affected. The arabic figures indicate numbers of unaffected children, Nine generations 
(I-IX) are illustrated. 
g =males, 9 =females. 
of villages in the south of France, in which many members have suffered 
from what is known as night-blindness, the affected persons being quite 
unable to see in a dim light. The pedigree commences with one Jean 
Nougaret, born in 1637, and has been followed through ten generations. 
In this family the disease has always behaved as a Mendelian dominant, 
though not a simple one, and it has always been inherited from 
an affected parent. Unaffected parents have never had affected 
descendants. 
In another disease, heemophilia, there is a curious relation with sex. 
