142 NATURE STUDY 



not to be told, but if possible to be brought out by the observation 

 of the pupils.) 



First of all, feathers are different in kind and have different 

 uses. The most characteristic, or special use is for flight. For 

 the water birds the feathers are arranged as a boat in which the 

 body can float. The bird would sink without its feathers. For all 

 birds, feathers keep warm in cool weather, protect from the rays 

 of the sun in hot weather, protect from rain, from scratches and 

 other mechanical injury in flying, or in running thru brush, etc. 

 They serve as ornamentation to distinguish each other and to 

 attract mates. 



Examination of feathers. To have a basis for comparison 

 examine the parts of a single feather, e. gr., a wing feather (fig. 80). 

 It possesses an axis, running its length, called the stem,. The 

 hollow part is the quill. The whole of the broad portion is the 

 vane. The axis of the vane is the raehis. The branches of the 

 rachis are the barbs^ and the minute branches of the barbs are 

 the barbules. 



The wing feathers and often the tail feathers are large and 

 strong. The barbs and barbules of each feather adhere quite 

 firmly, and the feathers overlap so that when the wing is extended 

 it presents a broad, firm surface with which to strike the air. 

 Have the pupils separate the barbs and barbules, smooth them 

 till they again adhere, and examine them with a microscope or 

 hand lens to determine how they adhere. 



The contour feathers are those all over the body whose ends 

 come out on the surface and overlap one another like shingles 

 on a house. The barbules on the outer ends adhere as in the 

 wing feathers. These thus fitting over each other make the out- 

 line of the body, and when well oiled, as they are in many birds, 

 they make a good waterproof coat. The inner ends have barbs 

 and barbules, very fine and not united, being downy. 



The down feathers have all their barbs very fine and diffuse. 



