The Making of Species 
in certain species, so in some cases are certain 
characters correlated with sex. 
Why this should be so we are not in a position 
to say; this, however, does not affect the indis- 
putable fact that such correlation does exist. 
Physicians in the course of their practice 
sometimes come across very curious cases of 
correlation in human beings. 
“It is,” writes Thomson (/evedzty, p. 290), 
“an interesting fact that an abnormal element in 
the inheritance may find expression in the males 
only or in the females only. If we could under- 
stand this we should be nearer understanding 
what sex really means. 
‘‘Hemophilia, or a tendency to bleeding, is 
a heritable abnormality, partly associated with 
weakness in the blood-vessels, which do not 
contract as they should and are apt to break, 
and partly connected with a lack of coagulating 
power in the blood. It is usually confined to 
males. But as it passes from a father through a 
daughter to a grandson, and so on, it must be a 
latent part of the germinal inheritance of the 
females, though for some obscure physiological 
reason it fails to find expression in them, or has 
its expression quite disguised. Colour-blindness 
or Daltonism has been recorded (Horner) through 
the males only of seven generations. Dejerine 
cites another case (fide Appenzeller) in which all 
the males in a family history had cataract through 
340 
