328 ELEMENTARY ZOOLOGY 



the bill) covered with horny substance. This horny sub- 

 stance together with the feathers and horny covering of 

 the feet are modified portions of the skin. Note the long 

 quill-feathers attached to the posterior edge of the wing. 

 By these the bird sustains its flight. Other long quill- 

 feathers are attached to the posterior end of the body, 

 forming the tail. By a system of muscles connected with 

 these feathers they act together, serving as a rudder during 

 flight and as a balancing contrivance when perching. 

 Note just above the bill two openings protected by tufts 

 of feathers. What are these openings ? How are they 

 connected with the moutli f Note the large eyes, and at 

 the inner angle of each the delicate nictitating membrane 

 which can be drawn over the ball. Does the bird have 

 external ears ? Lift the feathers just above the tail (the 

 upper tail-coverts) and note a small median gland, the 

 oil-gland, from which the bird derives the oil with which 

 it oils its feathers. Beneath the tail note the opening 

 from the alimentary canal and from the kidneys and 

 reproductive organs. This is called the cloaca! opening. 



Examine in detail some of the feathers. In one of the 

 quill-feathers note the central stem or shaft composed of 

 two parts, a basal hollow quill, which bears no web and 

 by which the feather is inserted in the skin, and a longer, 

 terminal, four-sided portion, the rachis, which bears on 

 either side a web or vane. Each vane is composed of 

 many narrow linear plates, the barbs, from which rise 

 (like miniature vanes) many barbules. Each barbule 

 bears many fine barbicels and hamuli or hooklets. The 

 barbs of the feather are interlocked. How is this effected ? 

 The feathers which overlie the whole body and bear the 

 color pattern are called contour -feathers. How do they 

 differ from or correspond with the quill-feathers in struc- 

 ture ? Soft feathers called down-feathers, or plumules, 

 cover the body more or less completely, being, however, 



