THE VERTEBRATES 431 



355. Feathers of birds deserve special examination. 

 They are closely allied to scales, and sometimes (e.g., on wings 

 of penguins) look like scales. 



(L) Examine a feather. Note stem, consisting of quill and 

 shaft. Examine a stem split lengthwise. The side branches 

 of the shaft are called barbs, and their smaller branches are barbules. 

 Examine with a hand-lens and note how the barbs and barbules 

 unite to constitute the vane of the feather. The barbules near the 

 edge of the feather on the side (lower) next to the bird's body have 

 smaller processes (barbicels) with hooks. 



The larger feathers of wings and tail (contour feathers) have stiff 

 shaft and firm vane. Down feathers have soft shaft and vane and 

 no hooks. Hair feathers are slender shafts with few or no barbs. 

 Examine a bird and note where each kind of feather is located. 

 What is the use of each kind ? 



A periodical change (molt) of feathers usually occurs in 

 autumn, to replace the feathers more or less damaged by 

 wear. Many birds also molt in part during the spring when 

 acquiring the breeding plumage; but the change in color 

 commonly seen is due largely to a change in the old feathers. 

 The new feathers are formed in the follicles or feather-tubes 

 in the skin, and first appear as pointed rods ("pin feathers"), 

 which are really the stems inclosing the forming vanes. 

 Examine such young feathers, either fresh or preserved in 

 alcohol. 



Color of birds is usually in the feathers, but sometimes in 

 comb and wattles of head and neck. Feather colors are 

 usually due to pigments (blacks, browns, reds, yellows, 

 rarely greens) ; but metallic luster or iridescent colors 

 are produced by the feather refracting or dispersing light 

 as prisms or thin plates of various transparent substances 

 do (e.g., rainbow colors). Blues, violets, and greens are 

 commonly due to a combination of pigments and light re- 

 fraction. There is no blue pigment in bird feathers. 



356. Internal Organs of Birds. Time available for this 

 course will not permit dissection of a bird, but students 



