TYPES or FEATHERS. 



Fig. 2. Sections of a central 

 ri^id feallier of the Lyre- 

 bird. Natural size;" a, 

 from terminal curve; 6, 

 middle portion. 



8), and booklets {hamuli; pi. i, fig. 8). These are simply a sort of fringe 

 to the barbules, just as if the lower edge of the barbule were frayed out, 

 and only differ from each other in one being plain, 

 hair-like processes, and the other being hooked at the 

 end. Barbicels do occur on both anterior and pos- 

 terior rows of barbules ; but rarely on the latter ; 

 booklets are confined to barbules of the anterior 

 series, which, as we have seen, overlie the posterior 

 rows of barbules, diagonally forming a meshwork. 

 The beautiful design of this structure is evident ; by 

 it, the barbules are in(e7'locked, and the vane of the 

 feather made a web ; for each booklet of one barbule 

 catches hold of a barbide from the next barb in front, 

 — any barbule thus holding on to as many of the bar- 

 bules of the next barb as it 

 has booklets. To facilitate 

 this interlocking, the bar- 

 bules have a thickened upper edge of such size 

 that the booklets can just grasp it. This is clear- 

 ly illustrated in pi. i. fig. 2, where a, a, a, a are 

 four barbs in transverse section, viewed from the 

 cut surfaces; with their anterior (b, b, b, b), and 

 posterior (c, c, c, c) barbules, the former bearing 

 the booklets which catch over the edge of the 

 latter. 



b. But all feathers do not answer the above 



description. First, the after-shaft may be wanting, as 

 we have seen ; then, as frequently happens, booklets 

 may not be developed, and barbicels may be few or 

 wanting ; barbules may be few or wanting, or so trans- 

 formed as to be only recognized by position, and even 

 barbs themselves may be wanting on one side of the 

 shaft, as in some tail feathers of the famous Lyre-bird, 

 or on both sides, as in certain bristly feathers about the 

 r mouth and eyelids of various birds. (Certain unusual 

 styles of feathers are shown in figs. 1, 2, 3.) Con- 

 sideration of these and other modifications has led to 

 the recognition of t/ii'ee 



§ 4. Types of Structure. 1. The feathery (pen- 

 nacea), characterized as above. 2. The downy {plum- 

 ulacea), when the stem is short and weak, with soft 

 rhacbis and barbs, with long, extremely slender, mostly 

 thread-like barbliles, with- little knotty dilatations in 

 place of barbicels, and no booklets. 3. The hairy (JiJoplumacea) with a 

 thin, stifi" calamus, usually no pith in the rhacbis, fine cylindrical stiif barbs 



Fia. 1. Section from loosely barbed 

 feather of Lyre-bird. Natural 



size. 



^IG. 3. a ; section, 1-2 size, 

 from one of tlie external 

 feathers of Lyre-bird ; 6, 

 single barb. 



