v . COLOURS OF ANIMALS 375 



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- 



