EVOLUTION OF THE COLORS OF BIRDS. 193 



feather, indeed, is white. A conspicuous line of white 

 is thus begun down the middle of the rump and car- 

 ried out on these two tail feathers. As the tail is flat- 

 tened against the tree these feathers would stand out 

 very distinctly and a broad line of white would be the 

 result, very characteristic of the bird in question. The 

 barring is of no utility, but a mere repetition of the 

 tendency to form bars on the outer tail feathers, as is 

 shown by the fact that the bars become obliterated with 

 advancing age, until in highly plumaged individuals 

 these inner tail feathers are almost uniformly black on 

 the outer and white on the inner side of the shaft. 



RECOGNITION MARKS. 



We may now consider the subject of color markings 

 from an entirely new point of view. Thus far the 

 question has been looked upon largely, if not entirely, 

 from the standpoint of the dead bird. An attempt has 

 been made to show that both the distribution of pig- 

 ment upon the feather and the formation of general 

 patterns of color were to a greater or less extent de- 

 pendant upon the laws of growth resident within the 

 organism. In considering this problem, however, the 

 ubiquitous natural selection was constantly dogging our 

 footsteps and demanding a hearing, but it is now time 

 to listen to its cause argued by an advocate for its rights 

 and not simply tolerate its presence as a necessary evil. 



Darwin was inclined to attribute the diversity of color 

 in birds rather to the action of sexual selection than to 

 natural selection. Accordingly such instances as the 

 conspicuous white tail of the rabbit he found difficulty 

 in explaining. It is to Wallace that we must turn for 

 an elucidation of the real meaning of these conspicuous 

 colors. He has shown that a large number of color 

 13 



