44 BRITISH BIRDS. 



sexes, though in some individuals the bristles are more 

 numerous, and consequently more easily seen, than in 

 others. 



It is quite useless to attempt to speculate on the causes 

 by which these feathers have been modified, or of what 

 use, if any, they are in the bird's economj^ Were they 

 confined to one sex and conspicuously coloured, some 

 zoologists would at once put do^^^1 their origin to sexual 

 selection, but as these conditions do not apply, they must 

 have arisen through some other cause. It has been 

 tentative^ suggested that by their hardness they help 

 to protect the bird's head when pushing through the 

 reeds, though in no individual do they appear numerous 

 enough to have much practical effect, and even if without 

 them the feathers did get more Avorn and rubbed, it is 

 difficult to see how such a result could be sufficient^ 

 powerful to lead to their development and perfection. 

 In fact, so far as we can see, there seems no obvious 

 reason which has led to their evolution, and it is worth 

 bearing this fact in mind at a time like the present, when 

 specialized structures are often plausibly accounted for 

 as having been developed under the stress and through 

 the workings of Natural Selection alone. 



