2 STEUCTURE OF FEATHERS. 



plates ill it, eight muscles on it, and a peculiar vascular organ inside ; two 

 larynges, or " Adam's-apples " ; two bronchi; two lungs, iDerfbrated to send 

 air into various airsacs and even the inside of bones ; four-chambered heart, 

 with perfect double blood-circulation ; tongue with several bones ; two or 

 three stomachs ; one liver, forked to receive the heart in its cleft ; gall- 

 bladder or none ; more or less diffuse pancreas, or "sweetbread" ; a spleen ; 

 intestines of much the same size throughout; ccBca, or none : two lobulated, 

 fixed kidneys ; two testicles fixed in the small of the back, and subject to 

 periodical enlargement and decrease ; one functional ovary and oviduct ; 

 outlets of these last three organs in an enlargement at end of intestine, and 

 their products, with refuse of digestion, all discharged through a common 

 orifice. But of all these, and other characters, that come under the head 

 of description rather than of definition, one is peculiarly characteristic of 

 birds; for every bird has feathers, and no other animal has feathers. 

 Naturally, then, we look with sjDccial interest upon 



Feathers : 



§ 3. a. Their Structure. A perfect feather consists of a main stem, 

 or scape (scapus; pi. i, fig. 7, ad), and a supplementary stem or after- 

 shaft (hyporhachis ; pi. i, fig. 7, b), each bearing two webs or vanes {vex- 

 illum, pi. vexilla; pi. i, fig. 7, c), one on either side. The scape is divided 

 into two parts; one, the tube or barrel, or "quill" proper {calamus; pi. i, 

 fig. 7, d) is hard, horny, hollow, cylindrical and semitransparent ; one end 

 tapers to be inserted into the skin ; the other ends, at a point marked by 

 a little pit (^umbilicus) , in the shaft (t^hachis) , or second part of the stem ; 

 the rhachis is squarish, and tapers to a point; is less horny, is opaque, and 

 filled with white pith ; it alone bears the vexilla. The after-shaft has the 

 same structure, and likewise bears vexilla ; it springs from the stem, at junc- 

 tion of calamus and rhachis, close by the umbilicus. It is generally very 

 small compared with the rest of the feather ; but in a few birds is quite as 

 large ; it is wanting in many ; and is never developed on the principal wing 

 and tail feathers. The vane consists of a series of appressed, flat, narrowly 

 lance-shaped or linear laminae, set obliquely on the rhachis, and divarica- 

 ting outward from it at a varying angle ; each lamina is called a barb 

 (barba; pi. i, fig. 6, a, a). Now just as the rhachis bears barbs, so does 

 each barb bear its vanes (barbuhs; pi. i, fig. 6, b, b, c) ; it is these last 

 that make a vane truly a iveb, that is, they connect the barbs together, so 

 that some force is required to pull them apart. They are to the "barbs ex- 

 actly what the barbs are to the shaft, and are similar^ given ofi" on both 

 sides of the barbs, from the upper edge of the latter. They are variously 

 shaped, but generally flat sideways, with ujoper and lower border at base, 

 rai^idly tapering to a slender thread-like end ; and are long enough to reach 

 over several barbules of the next barb, crossing the latter obliquely. All 

 the foregoing structures are seen with the eye or a simple pocket lens, but 

 the next two require a microscope; they are barbicels (or cilia; pi. i, fig. 



