THE STRUCTURE OF A FEATHER 261 



you will hardly be able to recognise it except by 

 counting the joints of the fore-limb. Nearer to 

 the body comes the long row of secondaries, inserted 

 into the ulna (one of the two bones of the fore-arm). 

 The bases of the quills are bare and separated, to 

 allow freedom of movement during the expansion and 

 folding of the wing, but air is not allowed to rush 

 through the intervening spaces, and so diminish the 

 force of the wing-stroke. The spaces are concealed 

 by the overlapping wing-coverts (upper and under). 

 The tail usually bears twelve quills, and has upper 

 and under tail-coverts. Notice the little "bastard- 

 wing " on the thumb, which perhaps you may not see 

 quite at the first glance. The feet are, in most Birds, 

 bare of feathers and scaly. It is easy to see that 

 feathered shanks and toes would be inconvenient to 

 Birds that run about on wet or muddy ground. 



Besides the quills a Bird carries body-feathers of 

 two or three sorts. The larger ones come to the 

 surface, and are hence termed, together with the 

 quills, contour feathers. They are compact and glossy, 

 at least in that part which is exposed, and overlap so 

 as to turn the rain. Hidden beneath them are fluffy 

 down feathers, which entangle much air. Air is more 

 important than the solid substance of the feathers 

 in preventing the escape of heat. There are also 

 filoplumes, feathers reduced to slender, wiry shafts with 

 perhaps a few plumes on one side, or a little tuft on 

 the summit. I suspect that the filoplumes help 

 to prevent the feathers, and especially the down 

 feathers, from becoming entangled one with another. 

 The stiff bristles often scattered through the fur 



