ORNAMENTAL PLUMES 155 



highly complicated structures could have evolved 

 from a section of tough horny integument. 



For the purpose of analysis let us take an ordi- 

 nary feather a primary from the wing. On 

 close inspection we discover that it is composed, 

 so to speak, of five different units. The basal 

 portion the hollow transparent stem is termed 

 the " calamus " or barrel. The opaque shaft 

 (vane), or ' l rachis, ' ' runs as a continuation of this 

 to the tip. The " feathering" branches out from 

 the shaft on two not quite opposite sides in num- 

 erous lateral shoots. These are designated as 

 barbs or "rami." They appear to the naked eye 

 to be long, flat, narrow, and solid, like the petal of 

 a daisy, and they radiate diagonally from the 

 shaft, one above the other. But a glance through 

 a microscope shows each barb to be a miniature 

 feather, with shaft and tiny lateral filaments of 

 its own, resembling the plumed antennae of a Ce- 

 cropia moth. The lateral filaments, termed 

 "barbules," interlock with the barbs above and 

 below them, being fringed with a series of minute 

 hooks, or "barbicels," which act as fasteners. 

 Thus, a tight, compact web is formed, giving the 

 strength to the feather necessary to enable it to 

 resist the pressure of the air. 



If a split occurs in the webbing, as often hap- 

 pens when the bird is alive, a few strokes of the 

 bill serve to readjust the barbicels so that they 

 will renew the grip they have lost. A person also 



