10 



EXTERNAL PARTS 



but form the best and lightest of all flying organs. Some 

 study of the parts of feathers and a knowledge of the descrip- 

 tive terms applied to them are important. 



Parts and kinds of feathers. — Every feather ^ consists of the 

 main scape, or stem, and the two webs. The scape has first the 

 hollow portion, the calamus or quill, and then the four-sided 



solid portion, the 

 rhachis, which ex- 

 tends to the tip of 

 the feather. The 

 rhachis bears on 

 each of its sides 

 lateral processes 

 called barbs. 

 These, with the 

 rhachis, form the 

 spreading portion 

 of the feather, the vane. The calamus has an opening at the 

 bottom through which the pulp penetrates, and another open- 

 ing, the superior aperture or umbilicus, on the lower side where 

 the calamus joins the rhachis. 



The barbs are narrow plates obliquely joining the rhachis, 

 and tapering to points at their free ends, their edges being 

 directed upward and downward when the vane is horizontal. 

 On the sides of the barbs are minute processes, called barbules, 

 branching from the barbs as the barbs branch from the rhachis. 

 These barbules are often serrated and terminated by little 

 hooks which interlock with hooks on the next barbule. (All 

 these parts can be seen with the naked eye, or by the aid of a 

 magnifying glass. With a microscope, the barbules 

 will be found to divide again into barbicels or cilia 

 and hooMets, forming a fringe to the barbules.) This 

 gives firmness to the vane. If there is no inter- 

 locking of barbules, downy ^ feathers are formed. Sometimes 

 the scape is very long, and the barbs are very short; such 

 feathers are called filament ^ feathers, or filoplum.es. 



