82 STRUCTURE AND COMPARISON. 



plumes would be wholly useless for flight even if the wings 

 were large enough to lift the bird. 



In the long feathers of the peacock's tail-coverts we see a 

 feather that is fringed with scattered disconnected barbs near 

 the base, but is tipped with interlocking barbs. We notice too 

 that the barbs are set upon the shaft at an angle, so that where 

 they come close together they overlap like clapboards on a 

 house ; and the barbules, being hooked at the end, catch hold of 

 the barb next in front of them, and hold to it. Thus at the tip 

 of the peacock's feather there is the beginning of a true web. 

 The barbules, we notice, are all upon the upper side of the 

 barb, or upon the upper edge of the barb-shaft, if we observe 

 more closely ; for the barb-shafts have been greatly flattened, 

 and they lie side by side like the thin leaves we see beneath 

 a toadstool on turning it over. This is an arrangement to 

 give stiffness without increasing the weight, and it greatly 

 strengthens the feather to bear the upward pressure of the air. 



In the hawk and eagle this arrangement is even more remark- 

 able, though we cannot see it so easily. And in these strong- 

 flying birds the barbules interlock much more firmly, so that 

 the feather is impervious to air, and is stiff enough to resist 

 the pressure of the wind. 



Without a microscope we cannot see the little barbicels, split 

 up like shavings partly cut from a stick, and like them hooked 

 at the ends, which reach out from barbule to barbule binding 

 the feather together still more closely. Some of the other 

 arrangements are too minute to be seen by the naked eye and 

 not easily understood from description, but in every part we 

 find the feather wonderfully planned to resist the pressure of 

 the air without the slightest unnecessary weight. 



These little barbules have to hold tight to each other; for 

 if they lost their grip the wind would blow up through the 



