TYPES OF FEATHERS. 3 
8), and hooklets (hamuli; pl. 1, 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, 
fj 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; 
hooklets are confined to barbules of the anterior 
/| series, which, as we have seen, overlie the posterior 
1) vows of barbules, diagonally forming a meshwork. 
| The beautiful design of this structure is evident; by 
| it, the barbules are interlocked, and the vane of the 
feather made a web; for each hooklet of one barbule 
\ catches hold of a barbule from the next barb in front, 
—any barbule thus holding on to as many of the bar- 
Fic. 2. Sections of a central * 
rigid feather of the Lyre- bules of the next barb as it 
ee ee? & has hooklets. ‘To facilitate 
this interlocking, the bar- _ 
bules haye a thickened upper edge of such size — 
that the hooklets can just grasp it. This is clear- 
ly illustrated in pl. 1. fig. 2, where a, a, a, a are 
four barbs in transverse section, viewed. from the ; 
cut surfaces; with their anterior (0, 6, 6, 6), and ~ 
posterior (c, ¢, c, ¢) barbules, the former bearing 
the hooklets which catch over the edge of the 
> Fig.1. Section from loosely barbed 
latter ~ feather of Lyre-bird. Natural 
size. 
6. But all feathers do not answer the above 
description. First, the after-shaft may be wanting, as 
we have seen; then, as frequently happens, hooklets 
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 hoth sides, as in certain bristly feathers about the 
, 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 three 
§ 4. Types or Srrucrurre. 1. The feathery (pen- 
y nacea), characterized as above. 2. The downy (plum- 
SS # ulacea), when the stem is short and weak, with soft 
Bifom one ot the eatemai Lhachis and barbs, with long, extremely slender, mostly 
single barb. "3" thread-like barbules, with little knotty dilatations in 
place of barbicels, and no hooklets. 3. The hairy (filoplumacea) with a 
thin, stiff calamus, usually no pith in the rhachis, fine cylindrical stiff barbs 
4 
. 
¢ 
7 
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