The Making of Species 
ally a hen golden pheasant assumes the plumage 
of the cock, but she never acquires the yellow 
eye. 
Many birds when kept in captivity lose some 
of the beauty of their plumage, and this is 
usually attributed to the sexual organs becoming 
impaired and reacting on the somatic tissue. 
But this explanation cannot in all cases be the 
correct one, because the linnet, although losing 
the male plumage in captivity, lives long and 
well in a cage and breeds readily with hen 
canaries. 
Another curious fact is that the male plumage 
sometimes appears pathologically in hen birds, 
more especially in those which have become sterile 
from age or disease. This phenomenon occurs 
comparatively frequently in the gold pheasant, 
and more rarely in the common pheasant, the 
fowl, and the duck. 
Phenomena such as these seem to suggest 
that in some cases the bright colours of the male 
may be pathological, that the hormones which 
the male sexual cells secrete may exercise an 
injurious effect on the somatic or body tissues. 
Decay is known to be accompanied by the 
production of brightly coloured pigment in the 
case of leaves. Finn suggests that the white 
plumage which the cock paradise fly-catcher . 
assumes in the fourth year of his existence may 
be a livery of decay, a sign of senility. 
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