84 GENERAL ORNITHOLOGY. 



the sheath that contains it peels off. The innermost layer simply sheathes the pulp, and is 

 finally transformed into the pith which may be observed inside the hollow quill as a set of little 

 caps or thimbles. Such development of feathers as is here briefly sketched holds good both for 

 neossoptiles and for teleoptiles, the formation of the latter simply completing the process begun 

 with the former. When the final feather has completed its growth the activity of the follicle 

 ceases as long as the feather stays in place ; but when the feather drops, as it always does when 

 it is worn out, the follicle renews its function and grows another feather in the same manner as 

 before, except that this teleoptile is never preceded by a neossoptile. The steps of the process 

 by which a feather expands into its complex figure from such a simple matrix or mould of form 

 is thus graphically illustrated by Huxley : 



" The integument of birds is always provided with horny appendages, which result from the conversion into horn of 

 the cells of the outer layer of the epidermis. But the majority of these appendages, which are termed ' feathers,' do not 

 take the form of mere plates developed upou the surface of the skin, but are evolved within sacs from the surfaces of con- 

 ical papillfe of the dermis. The external surface of the dermal papiUa, whence a feather is to be developed, is provided 

 upon its dorsal [upper] surface with a median groove, which becomes shallower towards the apex of the papilla. From 

 this median groove lateral furrows proceed at an open angle, and passing round upon the under surface of the papilla, be- 

 come shallower, until, in the middle line, opposite the dorsal median groove, they become obsolete. Minor grooves run 

 at right angles to the lateral furrows. Hence the surface of tlie papilla has the character of a kind of mould, and if it 

 were repeatedly dipped in such a substance as a solution of gelatine, and withdrawn to cool until its whole surface was 

 covered with an even coat of that substance, it is clear that the gelatinous coat would be thickest at the basal or anterior 

 end of the median groove, at the median ends of the lateral furrows, and at those ends of the minor grooves which open 

 into them ; while it would be very thin at the apices of the median and lateral grooves, and between the ends of the minor 

 grooves. If, therefore, the hollow cone of gelatine, removed from its mould, were stretched from within ; or if its tliin- 

 nest parts became weak by drying ; it would tend to give way, along the inferior median line, opposite the rod-like cast of 

 the dorsal median groove and between the ends of the casts of the lateral furrows, as well as between each of the minor 

 grooves, and the hollow cone would expand into a flat feather-like structure with a median shaft, as a ' vane ' formed of 

 'barbs' and 'barbules.' In point of fact, in the development of a feather such a cast of the dermal papilla is formed, 

 though not in gelatine, but in the homy epidermic layer developed upon the mould, and, as this is thrust outward, it opens 

 out in the manner just described. After a certain period of growth the papilla of the feather ceases to be grooved, and a 

 continuous horny cylinder is formed, which constitutes the 'quiU.' " (Introd. Classif. Auim., p. 71.) 



Structure of Feathers. — A perfect feather, possessing all the structures a teleoptile can 

 have developed, consists of the following named parts : (1) a main stem, shaft, or scape in 

 two portions, calamus and rliachis / (2) a supplementary stem, aftershaft, or hyporliachis ; 

 (3) each stem bearing on each side a web, vane, or vexillum ; (4) each web composed of a 

 series of bai-bs or rami ; (5) each barb bearing on each side a series of barbules or radii ; 

 (6) most barbules bearing a set of barbicels or cilia ; (7) some barbicels forming booklets or 

 hamuli. Exactly how these several parts or structures combine to compose the feather is next 

 to be shown. 



(1) The main stem, shaft, or sca2)e (Lat. scapus, a stalk) is usually divided into two well 

 distinguished parts, calamus and rhachis. (a) The calamus (Lat. a reed) is the part next the 

 body of the bird inserted by one end into the skin, and at the other end supporting the rest 

 of the feather. This is the tube, barrel, or ''quill" proper; a hard, horny, hollow, semitrans- 

 parent cyHuder, bearing no webs, and containing on the interior a little loose dry pith in the 

 form of a series of caps or thimbles, sometimes called the " soul." These are the remains 

 of the innermost layer of the inner division of the Malpighian stratum. One end of this 

 quill tapers to its insertion, and is matked by the trace of what was an opening when the 

 featlier was growing; this is the umbilicus inferior. The other end of the calamus passes 

 dii-ectly into the rhachis, at a point marked by a little pit, the umhilicus superior, on the under 

 side of the feather (nearest the bird's body). The rhachis (Gr. pdxts, rhachis, a spine or ridge) 

 is the direct continuation of the calamus to the tip of the feather, but (lifters in cliaracter, being 

 a four-sided prism, squarish in cross section, tapering gradually to a fine point : it is less horny 

 than the barrel, very elastic, opaque, and solidly pithy; it alone bears the vexilla, serving as 

 a midrib between the two vanes for their whole extent. Tlie rhachis is usually grooved length- 



