382 



ZOOLOGY 



SECT. 



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 

 together by extremely delicate oblique filaments, the barbules, 

 having the same general relation to the barbs as the barbs them- 

 selves to the rachis. 



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

 only by microscopic examination. Each barb (Fig 1024, 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 



FIG. 1024. 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 Headlcy, 

 after Py craft.) 



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 

 barbules of the barb immediately distal to it (A). The lower edge 

 of the distal barbule is produced into minute hooJdets (D) : in 

 the entire feather the booklets of each distal barbule hook over 

 prominent flanges of the proximal barbules with which it is in 



