STRUCTURE OF FEATHERS. II 



animals, any living member of which may be recog- 

 nized, as already said, by the possession of feathers. 

 So highly modified has the original type become, that 

 it is one of the triumphs of modern science to have 

 traced the lineage of birds back to its point of depart- 

 ure from reptiles. 



Structure of Feathers. A perfect feather, that is, 

 one possessing all the parts a feather can have, con* 

 sists of a main stem, or central shaft, and a supple- 

 mentary stem, or after-shaft; each of these bearing 

 two webs or vanes, one on each side. The main stem 

 is divided into two parts : the hard, horny, hollow por- 

 tion next to the skin, and the softer, pithy part, which 

 alone bears the vanes. At the point where the web 

 begins there is a little pit, called the umbilicus. The 

 after-shaft is of similar structure and likewise bears 

 webs ; it springs from the main shaft near the umbilicus ; 

 it is commonly smaller than the rest of the feather, and 

 is often wanting ; it is not developed on the large stiff 

 feathers of the wings and tail. The vane of a feather 

 consists of a number of flat, narrowly-linear plates 

 closely packed together, standing out from the shaft at 

 a varying oblique angle. Each such plate, or lamina, 

 is called a barb ; and each barb bears a series of pro- 

 cesses or offsets called barbules, just as the stem bears 

 the barbs. It is these lesser processes that confer co- 

 herency upon the barbs, making the vane a web. 

 For they are variously fringed with still lesser pro- 

 cesses called barbicels and booklets, the interlocking 

 of which gives consistency to the whole feather. 



Many feathers, however, do not answer to any such 

 description, feathers being endlessly modified in the 

 details of their structure in different birds and on dif- 



