The Integumentary System 89 



ceedingly light in weight, thus giving warmth and support and adding 

 little to the total weight of the bird; and they offer broad surfaces for 

 aid in flying. Feathers are epidermal in origin and are considered to 

 be highly modified scales. 



Three types of feathers (Fig. 25) can be distinguished in birds. 

 The largest and most conspicuous of these are the quill feathers. These 

 include the feathers of the wings, tail, and the large contour feathers 

 that clothe the body. All surfaces of the body do not have these feathers, 

 rather they are arranged in definite patches and tracts. The naked 

 areas between the feather tracts are not unprotected, for the large con- 

 tour feathers overlap to cover them. 



Fig. 25. — Types of feathers. A, Contour; B, enlarged portion of contour; 



C, filoplume; D, down. 



Beneath the large contour feathers are the smaller down feathers. 

 These are close to the skin and provide insulation. In the young 

 bird they are the main feathers seen, but they are soon concealed by 

 the developing contour feathers. 



The third type of feathers are the filoplnmes which superficially 

 look like hairs. They are scattered over the body among the contour 

 feathers. 



The structure of one of the large wing feathers may be considered 

 as typical. The basal portion of the feather is the hollow quill which 

 narrows distally into the shaft. There is a small opening at the base 

 of the quill and another at the apex. The expanded portion of the 

 feather is the vein which consists of harhs and barbules. The barbules 

 have tiny hooks which interlock to form a broad smooth surface for 

 flight. If this smooth surface is in some way broken, the bird easily 

 repairs the damage by preening itself. 



