vex. 



FEATHERS 395 



first, as in many other birds, is small and not easily visible. 



The bastard wing is a small tuft of feathers at the wrist. The tail 



bears twelve large feathers called 



rectrices and many coverts. The 



rest of the body is covered with 



numerous smaller feathers ; these are 



not uniformly distributed, but grow 



in tracts or pterylse, separated by 



bare patches or apteria (Figs. 308, 



309)- 



The structure of a feather is best 



seen in a quill or one of the larger 



coverts (Fig. 310). The stem or scapus 



is divided into a lower, hollow part, 



the calamus or quill, and an upper, 



solid part, the rachis. The quill is 



embedded in a pit of the skin and 



has at its lower end an opening, the 



inferior umbilicus, through which a 



vascular papilla projects into the 



growing feather. At the junction of 



the quill and rachis is a minute 



opening known as the superior 



umbilicus. Close to this arises a small 



tuft known as the aftershaft. The 



rachis is the axis of the flattened 



part of the feather known as the 



vexillum or vane. This is composed 



of a series of elastic plates set along 



the sides of the rachis with their fiat 



sides perpendicular to the plane of 



the vane. The plates are known as 



barbs (Fig. 311), and they are held 



together by barbules, which are 



smaller processes that fringe the 



barbs. The barbules of one side of a 



barb (distal barbules) bear Httle 



hooks or barbicels which catch upon 



the barbules of the adjoining barb. 



Thus the whole vane is held together and forms a single surface 



for striking the air. 



310. — Feathers 

 pigeon. 



A, Down feather; 5, filoplume ; 

 C, quill feather. 



a.s., Aftershaft ; i.u., inferior umbili- 

 cus ; qu., quill or calamus ; rch., 

 rachis or shaft ; s.m., superior 

 umbilicus ; vex., vexillum or vane. 



