EXTERNAL PARTS OF BIRDS. — FEATHERS. 



87 



in fact, the same feather may be constructed on more than one of these plans, in different 

 parts of its length, as in fig. 19, partly pennaceous, partly plumulaceous. All feathers are 

 built upon one or another, or some combination, or modification, of these types; and, in all 

 their endless diversity, may be reduced to four or five. 



Different Kinds of Feathers. — 1. Contour -feathers, pennts or pl!j««« proper, have a 

 perfect stem composed of calamus and rhachis, with smooth-webbed vanes of pennaceous 

 structure, at least in part, usually plumulaceous toward the base. 

 These form the great bulk of surface-plumage exposed to light ; 

 their beautiful tints give a bird its colors ; they are the most 

 modified in detail of all, from the fish-like scales of a penguin's 

 wings to the glittering jewels of a Humming-bird, and all the 

 endless array of tufts, crests, ruffs, and other ornaments of 

 the feathered tribes; even the imperfect bristle-like feathers 

 above mentioned may belong among them. The most conspic- 

 uous contour-feathers are the large ones of the wings and tail; 

 these are also the most perfect feathers, except for lack of an 

 aftershaft. Some contour-feathers are of fluffy texture, assume 

 singular shapes, and grow to great lengths ; such are commonly 

 ornamental, and may be confined to the nuptial plumage, or 

 characteristic of the male sex, as the aigrettes of many Herons, 

 and the plumas of Paradise birds. Such feathers may not only 

 lack all the minute structures above described, but even have the 

 webs decomposed, owing to fewness of barbules or of barbs them- 

 selves. It would take me too far afield to go fully into their 

 numerous variations. Contour-feathers are usually individually 

 moved by subcutaneous muscles, of which there may be sevei-al 

 to one feather, passing to be attached to the sheath of the tube, 

 iuside the skin, in which the stem is inserted. These muscles 

 may be plainly seen under the skin of a goose, and every one has observed 

 their operation when a hen shakes herself after a sand-bath, or erects her 

 top-knot, or any other bird ruffles up its plumage. 2. Down-feathers, plumulce, are charac- 

 terized by a downy structure throughout. They more or less completely invest the body, but 

 are almost always hidden beneath contour-feathers, like padding about the bases of the latter ; 

 occasionally they come ^ 



in 



Fk; 21.— 

 A single bar- 

 bule, bearing 

 barbicels and 

 booklets ;mag- 

 nifltil ; after 

 Nitzscb. 



Fig. 22. 

 Four barbs 

 cross section, a, 



a, a, a, bearing 

 anterior, b, b, b, 



b, and posterior 



c, c, c, c, bar- 

 bules, the form- 

 er bearing hook- 

 lets which catch 

 over the latter; 

 magnified; after 

 Nitzsch. 



\- 



y 



iR 



Fig. 

 entirely 



I the tail of a Kingbird. Tyrannus tyrnnnus, almost 

 Tshaft. From nature, by Coues. 



to light, as in the fleecy 



ruft' about the Condor's 



neck, and then usually 



replace contour-feathers ; 



tliey have an aftershaft, 



or none; sometimes no 



rhachis at all, the barbs then being sessile in a tuft at the end of the calamus. They often 



stand in a regular quincunx (] • ]) between four contour-feathers. All neossoptiles are of 



di)wny structure, though they belong to a different category of feathers, as we have seen, and 



we are now talking only of teleoptiles. Down-feathers, as a rule, are more copious in water 



birds than in land birds; swan's-down and eider-down are fine examples, and may be used by 



both birds and people to warm their respective nests. 3. Semiplumes, semiplwnce, may be 



said to unite the characters of the last two, possessing the pennaceous stem of the former, and 



the plumulaceous vanes of the latter ; they are with or without aftershaft. They stand among 



pcnnfe, as plumul* do, about the edges of patches of the former, or in parcels by themselves. 



