Page:The American Cyclopædia (1879) Volume VII.djvu/112

 104: FEATHERS K or beard. 4. cessory plume. The lower umbiii- called the pith, which supplies strength and nourishment to the feather. The vane consists of two webs, one on each side of the ^ shaft, each web being formed of a series of laminae or barbs, of varying thickness, width, and length, arranged obliquely on the shaft, and composed of the same material ; their flat sides are placed close to each other, enabling them to resist any ordinary force act- ing in the direction of their plane, as the impulse of the air in the act of flight, though yielding readily to any force applied in the line of the shaft. The barbs taper to a point, but are broad near the shaft, and in the large wing feathers the convexity of one is received into a concavity of another; but the barbs are kept in place chiefly by barbules, minute curved fila- ments arising from the upper edge of the barb, as the lat- ter does from the shaft ; there are two sets, one curved up- FIG 1 -Parts of the ward and the ther down - Feather. ward, those of one barb hook- 1. The quill. 2. The ing so firmly into those of tne next as to form a close , ., ., 5. and compact surface ; in the iii- ostrich the barbules are well ' Upperum ' developed, but are long, loose, and separate, giving that soft character conveyed by the term plume. The barbules are sometimes provided with a similar apparatus on their sides called barbicels, as in the quills of the golden eagle and albatross ; these serve to keep the barbules in position, but are less numerous than the latter. In most feathers there is an appendage near the upper umbilicus of a downy character, called the ac- cessory plume ; small in the quills of the wings and tail, in some body feathers of hawks, ducks, and gulls it is of large size, in some spe- cies as large as the feather which supports it ; 'in the emu two plumy feathers arise from one quill, and sometimes three in the cassowary, the additional plumes being these accessory feathers ; in the ostrich there is no such addi- tional tuft. There is, therefore, every grada- tion from a simple barrel and shaft, as in the cassowary's quills, to the feather with barbs, barbules, and barbicels. Some feathers are all downy, like the abdominal ones of the eagle- owl ; others have very little down, as the harsh plumage of the penguin ; in the eider duck, and other arctic species, there is at the base of the common feathers a soft downy covering, securing warmth without weight, like the soft fur at the base of the hair of arc- tic mammals; young birds are covered with down before the development of feathers, the latter being guided through the skin by the former. In the chick the formation of down begins on the eighth day of incubation, and is continued until the hatching; 10 to 12 radia- ting filaments are formed at the same time in an epidermic sheath, which soon after birth dries and sets free the plumes, allowing them to spread out as a pencil of down ; a stem is de- veloped, and the downy filaments become the primary web of the feather. Feathers in some cases resemble stiff bristly hairs, as about the bill in most birds, and the. tuft on the breast of the wild turkey. In the genus dasylophus, peculiar to the Philippine islands, we have re- markable instances of the modifications of the epidermic covering of birds. In D. Cumingii (Fras.), the feathers of the crest, breast, and throat are changed at their extremities into ovoid horny lamellae, looking like shining black spangles, expansions of the true horny structure of the shaft ; something of the kind is seen in the Bohemian chatterer or wax-wing (ampelis garrulus, Linn.), in which some of the secon- dary and tertial quill feathers end in small, oblong, flat appendages, in color and consis- tence resembling red sealing wax, which are also expanded horny prolongations of the shafts of the ordinary feathers. In D. superciliosus (Cuv.), the only other species of the genus, the feathers over each eye are changed for three fourths of their length into red silky hairs or bristles, the base of the feather having the usual appearance; each shaft seems to divide into several of these hair-like fila- ments, which are finer and more silky than the append- age on the breast of the tur- key, and directly continuous with ordinary feather struc- ture, while in the turkey there is a complete transfor- mation of feathers into hairs in the whole extent. In most birds there will be found a number of simple hair-like feathers scattered over the skin after they have been plucked ; they arise from short bulbs or slender round- ed shafts. Feathers are de- veloped in depressions in the skin lined by an inversion of the epidermis which sur- rounds the bulb ; they grow by the addition of new cells from the bulb, which become modified into the horny and fibrous stem, and by the elon- gation and extension of pre- viously formed cells ; like the hair, they originate in fol- licles producing epidermic cells, though when fully formed the cellular structure is widely departed from except in the medullary portion. They are, when first formed, living organized parts, developed from a matrix connected with the vascular layer Fie. 2. Matrix of a prowing Feather, laid open. ' the Ex- ternal membrane. 8, 3. Matter of the vane. 4. Inter- nal membrane. 5. Bulb, or medulla.