370 



ZOOLOGY 



SECT. 



superior umbilicus represents the after-shaft of many Birds- 

 including some Pigeons (vide infra). 



The vane has a longitudinal axis or rachis (rch.) continuous 

 proxirnally with the quill, but differing from the latter in being 

 solid. To each side of the rachis is attached a kind of membrane 

 forming the expanded part of the feather and composed of barbs 

 delicate, thread-like structures which extend obliquely outwards 

 from the rachis. In an uninjured feather the barbs are closely 

 connected so as to form a continuous sheet, but a moderate amount 

 of force separates them from one another, and it can readily be 

 made out with the aid of a magnifying glass that they are bound 



FIG. 1035. Structure of Feather. A, small portion of feather with pieces of two barbs, 

 each having to the left three distal barbules, and to the right a number of proximal barbules, 

 many of them belonging to adjacent barbs. B, booklet of distal barbule interlocking with 

 flange of proximal barbule. C, two adjacent proximal barbules. D, a distal barbule 

 (From Headley, after Pycraft.) 



together by extremely delicate oblique filaments, the barbules, 

 having the same general relation to the barbs as the barbs themselves 

 to the rachis. 



The precise mode of interlocking of the barbs can be made out 

 only by microscopic examination. Each barb (Fig. 1035, A) is a 

 very thin and long plate springing by a narrow base from the 

 rachis, and pointed distally. From its upper edge the edge 

 furthest from the body of the Bird spring two sets of barbules, a 

 proximal set (C) directed towards the base of the feather, and a 

 distal set (D) towards its tip. Owing to their oblique disposition 

 the distal barbules of a given barb cross the proximal barbules of 

 the next, each distal barbule being in contact with several proximal 



