32 BIEDS. 



(ii). The inner rectrices may be longer than the other ones. This form in 

 different degrees is called — 



"Bounded," as in the tail of the Mallard, which has 20 rectrices, of 

 which the four nearest the middle line are differently coloured from 

 the rest and curled upwards. In the female Wild Duck there are 

 18 rectrices, similar in colour, and the middle ones are not curled 

 upwards. 

 "Gradated," as in the Eook, 12 rectrices, and in the Bengal Eagle-Owl, 



12 rectrices. 

 "Cuneate," or "acute," as in the Magpie, 12 rectrices. 



"Long exserted." The two central feathers alone may be much longer 

 than the others, as in the Common Sand-Grouse, 16 rectrices. 

 (iii.) The outer feathers may be longer than the inner. This form is called, 

 according to the degree — 



" Emarginate," as in the House-Martin, 12 rectrices. 

 "Forked," or "forficate," as in the Swallow, 12 rectrices. 

 Special modifications of this forked form are called " lyrate," as in the Black 

 Grouse {T. tetrix), 18 rectrices; "racket-tailed," as in the Humming Bird 

 (<S. underwoodii), 10 rectrices. 



EXTERNAL COVERING, OR FEATHERS. 



A feather consists of a stem, shaft, or scape (scapus) forming its axis, and 

 bearing two webs, or vanes (vexilla), one on either side. 



The stem is divided into two parts, that nearest to the body of the bird is a 

 hard, hollow, horny, and semi-transparent cylinder called the "barrel," or "quill" 

 (calamus). One end of this is embedded in the skin, the other is continued into 

 the shaft proper (rhacTiis), which is four-sided, solid, elastic, and gradually tapers 

 to a fine point. It is longitudinally grooved on the under side, or that towards 

 the body of the bird. The stem has an inferior aperture at the apex, into which 

 the vascular pulp (" pith " of the dried feather) penetrates, and a superior aper- 

 ture (umbilicus) situated on its under surface at the junction of the calamus with 

 the rhachis. 



The vanes consist of a number of flat, narrow-pointed plates set obliquely on 

 the rhachis by their bases, called "barbs." The edges of the barbs bear numerous 

 smaller processes called " barbules." These in the most perfect feathers (those of 

 the " plumous '' or " pennaceous " type in the wing of an Argus Pheasant) are 

 fringed with still smaller " barbicels " and booklets (hamuli), by which the barbs 

 are held together so as to present a continuous resisting surface to the air. 



The various kinds of feathers are — 



I. Pennoe, or plumce proper, also called " contour feathers," because they Ue on 

 the surface and determine the contour of the body. They are exposed to the 

 light. They have a perfect stem and vanes, mostly of a pennaceous structure, 

 though generally more or less plumulaceous at the base. (They are distributed 

 evenly over the body only in a few birds, as the KATiiiE, the Penguins, and some 

 others.) Generally they are arranged in definitely circumscribed patches or bands, 

 between which the skin is either bare or covered only with down. 



