v COLOURS OF ANIMALS 875 
Without pretending to solve completely so difficult a 
problem as that of the origin and uses of the variously 
coloured plumes and ornaments so often possessed by male 
birds, I would point out a few facts which seem to afford a 
clue. And first, the most highly-coloured and most richly- 
varied markings occur on those parts of the plumage which 
have undergone the greatest modification, or have acquired 
the most abnormal development. In the peacock, the tail- 
coverts are enormously developed, and the “eyes” are 
situated on the greatly dilated ends of these elongated 
feathers. In the birds-of-paradise, breast, or neck, or head, 
or tail-feathers, are greatly developed and highly coloured. 
The hackles of the cock and the scaly breasts of humming- 
birds are similar developments ; while in the Argus-pheasant 
the secondary quills are so enormously lengthened and 
broadened as to have become almost useless for flight. Now 
it is easily conceivable that during this process of develop- 
ment inequalities in the distribution of colour may have 
arisen in different parts of the same feather, and that spots 
and bands may thus have become broadened out into shaded 
spots or ocelli, in the way indicated by Mr. Darwin, much 
as the spots and rings on a soap-bubble increase with increas- 
ing tenuity. This is the more probable, because in domestic 
fowls varieties of colour tend to become symmetrical, quite 
independently of sexual selection (Descent of Man, p. 424). 
This is one of those crucial facts which, on Mr. Darwin’s 
theory, ought not to happen, and which plainly indicate that 
symmetrical markings arise from the action of some general 
laws of colour-development. 
If now we accept the evidence of Mr. Darwin’s most 
trustworthy correspondents, that the choice of the female, so 
far as she exerts any, falls upon the “most vigorous, defiant, 
and mettlesome male;” and if we further believe, what is 
certainly the case, that these are as a rule the most brightly 
coloured and adorned with the finest developments of plum- 
age—we have a real and not a hypothetical cause at work. 
For these most healthy, vigorous, and beautiful males will 
have the choice of the finest and most healthy females, will 
have the most numerous and healthy families, and will be 
able best to protect and rear those families. Natural selec- 
