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 vi'hich the stem is inserted. These muscles may be plainly seen under the 

 skin of a goose, and every one has observed their operation vehen a hen shakes herself after a 

 sand bath, or any bird erects its top-knot. 2. Down-feathers, plumulce, are characterized by 

 a downy structure throughout. They more or less completely invest the body, but are almost 

 always hidden beneath the contour-feathers, Uke padding about the bases of the latter ; occa- 

 sionally they come to light, as in the tieecy ruff about the neck of the condor, and then usually 

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

 the barbs then being sessile in a tuft at the end of the quill. They often stand in a regular quin- 

 cunx (;•!) between four contour-feathers. 3. Semiplumes, semiplnmciE, may be said to unite 

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

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

 the plumulse do, about the edges of patches of the fonner, or in parcels by themselves, but are 

 always covered by contour-feathers. 4. Filoplumes, filoplumce, 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 accessories, 

 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 shown on domestic 

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

 table. 5. Certain do\vn-feathers are remarkable for continuing to grow indefinitely, and with 

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

 plumulse, from being always dusted over wdth dry, scurfy exfoliation, are called powder-down ; 

 they may be entitled to rank as 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, corresponding to the 

 sweat-glands and sebaceous fuUicles so common in Mammalia, are little known among them. 

 But their ' ' oil-can " is a kind of sebaceous follicle, which may be noticed here in connection 

 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 uropygial 

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

 called the elceodochon (Gr. eXaioBoxos, elaiodochos, containing oil). 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-hke elevation. 

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

 operation called "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 Unf eathered Spaces. — Excepting certain 

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

 fuUy feathered. So they are all covered with feathers, but it does not foUow that feathers are 

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

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



