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. 



338 



