ARRANGEMENT OF FEATHERS. 13 



usually present, or by their presence where generally absent. Most note- 

 worthy of such cases are the absence of feathers on the heads of some Vultures, 

 and the presence of feathers on the feet, and even the toes, of rtarniigans. 

 Many game birds have special bare spaces on the neck which are very promi- 

 nent in the male, during the breeding season. 



THE ORIGIN, GROWTH AND CARE OF FEATHERS. 



Birds have the thinnest skin of all vertebrates, and the feathers arise from 

 it as epidermal formations upon a dermal papilla. These epidermal structures 

 develope first as down-feathers, and their development may cease there, but in 

 most cases the embryonic down-feather is replaced by a definitive feather. 

 The second feather is formed directly beneath the first, and growing rapidly 

 punches the down-feather out of its place, and comes to the surface. In its 

 subsequent growth, one of the rays becomes rapidly thickened, and forms the 

 shaft of the completed feather, upon the sides of which develope the barbs. 

 Each growing feather is supplied with an artery and vein, which maintain an 

 active circulation. When the growth is completed, however, the artery and 

 vein, together with all the contents of the shaft and quill, become dried up, 

 and the feather is no longer a living part of the bird, but simply a bit of dead 

 skin. After a time, the feathers fall oft', and new feathers are formed to re- 

 place them, and this losing of the old feathers is called the moult. As a rule 

 moult is annual, but in some birds it is semi-annual. The annual moult occurs 

 late in the summer, and the semi-annual very early in the spring, but this 

 spring moult is often only partial. Ptarmigans are said to have a third moult 

 late in the fall. Most birds are very careful of their plumage and some spend 

 much time in cleaning, oiling and smoothing it. This process is spoken of as 

 preening and is especially characteristic of bright-plumaged and song birds. 

 Birds have no glands in the skin, but most species have a well-developed mass 

 of oil-glands on the back, just above the base of the rectrices and hidden by 

 the upper tail coverts. This mass is more or less triangular or heart-shaped 

 and opens by one or more pores at the tip of a nipple-like projection. This 

 projection is frequently surmounted by a circle of small feathers, around the 

 openings, known as the oil-gland tuft. The oil-gland is specially well-de- 

 veloped in water-birds, while in land-birds it is smaller and sometimes absent. 

 It is as large as a Pigeon's egg in the Pelican; it is wholly wanting in the 

 Ostrich and its allies. Its presence or absence, and whether "tufted" or not, 

 are important points in classification. The oil is pressed out by the bill of the 

 bird and then spread upon the feathers, thus helping to make the plumage 

 waterproof. 



THE COLOR OF THE PLUMAGE. 



The most conspicuous feature of the plumage of birds is undoubtedly the 



