86 GENERAL ORNITHOLOGY. 



them. Another feature is, that they are usually individually moved by subcutaneous muscles^ 

 of which there may be several to one feather, passing to be attached to the sheath of the tube, 

 inside 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 any bird erects its top-knot. 2. JDo«i;M-/ea</i«rs, ^Z«0MM?«e,Vre oliaractefized by 

 a downy structure throughout. They more or less completely investthe bqdy, but are almost 

 always hidden beneath the contour-feathers, like padding about the bases hi the latter ; occa- 

 sionally they come to light, as in the fleecy ruff about the neck of the cond'br, and then usually 

 replace contour-feathers ; they have an after-shaft, or none ; and sometiniBs no rhaonis at all, 

 the barbs then being sessile in a tufl at the end of the quUl. They often sta^d in a regular quin- 

 cunx (!•!) between four contour-feathers. 3. Semvplmms, semiplumm, may be said to unite 

 the characters of the last two, possessing the pennaceous stem of the forrtier, and the plumula- 

 ceous vanes of the latter ; they are with or without after-shaft. They stand among pennse, as 

 the pliimulas do, about the edges of patches of the former, or in parcels by themselves, but are 

 always covered by contour-feathers. 4. FiloplumeSf filopluma', or thread-feathers, have an 

 extremely slender, almost invisible stem, not well distinguished into barrel and shaft, and 

 usually no vane, unless a terminal tuft of barbs may be held for such. Long as they are, 

 they are usually hidden by the contour-feathers, close to which" they stand as accepsories, 

 one or more seeming to issue out of the very sacs in which the larger feathers ^are implanted. 

 These are the nearest approach to hairs that birds have ; they are very well sho*n on domestic 

 poultry, being what a good cook finds it necessary to singe off after plucking a fowl for the 

 table. 5. Certain down-feathers are remarkable for continuing to grow indefiiiitely, and with 

 this unhiriited growth is associated a continual breaking down of the ends of the' barbs. Such 

 plumnlsB, from being always dusted over with dry, scurfy exfoliation, are called powder-drnm; 

 they may be entitled to rank aa a fifth kind, or pulviplumes. They occur in the hawk, parrot, 

 and gallinaceous tribes, and especially in the herons and their allies. They are always present 

 in the latter, where they may be readily seen as at least two large patches of greasy or dusty, 

 whitish feathers, matted over the hips and on the breast. The design is unknown. 



Feather Oil Gland. — Birds do not perspire, and cutaneous glands, oolTesponding to the 

 sweat-glands and sebaceous follicles so common in Mammalia, are little known among tbim. 

 But their " oil-can" is a kind of sebaceous follicle, which may be noticed here m oonuection 

 with other tegumentary appendages. This is a two-lobed or rather heart-shaped gland, sad- 

 dled upon the "pope's nose," at the root of the tail, and hence sometimes called the m'opygial 

 (Lat. uropygium, rump), or rump-gland. If there be no single word to name it, it may be 

 called the elmodoehon (Grr. eXaioSdxos, daiodochos, containing oU). It is composed of numerous 

 slender tubes or follicles Which secrete the greasy fluid, the ducts of which, uniting successively 

 in larger tubes, finally open by one or more pores, commonly upon a little nipple-like elevation. 

 Birds press out a drop of oil vrith the beak and dress the feathers with it, in the well-known 

 operation caOed "preening." The gland is large and always present in aquatic birds, which 

 have need of waterproof plumage ; smaller in land-birds, as a rule, and wanting in some. The 

 presence or absence of this singular structure, and whether or not it is surmounted by a particu- 

 lar circlet of feathers, distinguishes certain groups of birds, and has come to be made much use 

 of in classification. 



Pterylography. —- Feathered Tracts and Unfeathered Spaces. — Excepting certain 

 birds having obviously naked spaces, as about the head or feet, all would be taken to be 

 fully feathered. So they are all CMered with feathers, but it does not follow that feathers are 

 everywhere implanted upon the skin. On the contrary, a uniform and continuous pterylosis 

 is the rarest of all kinds of feathering j though such occurs, almost or quite perfectly, among 



