EXTERNAL PARTS OF BIRDS. — FEATHERS. 



85 



wise on its under side, this groove being best marked on the large feathers of the wings and 

 tail ; and it is commonly much longer than the calamus. 



(2) The aftershaft or hyporhachis (Gr. vno, hupo, and pdxis), when well developed is like 

 a duplicate of the main feather, from the under side of the stem of which it springs, at junction 

 of calamus with rhachis, close by the umbilicus superior. It is generally very small in com- 

 parison with the main part of the feather, though quite as large in a few birds, as Cassowaries, 

 Emeus, and Moas. This counterpart or " counterfeit " is n(jt developed in all groups of 

 birds, nor on all feathers of any bird ; its presence or absence, whether by non-acquisition or 

 subsequent reduction, thus becomes a classificatory character of some importance. It is never 

 well developed, but generally minute or wanting on the large strong wing- and tail-feathers ; 



is best marked as an ap- 

 pendage of small contour 

 feathers, and especially 

 down feathers. The after- 

 shaft may bear vanes, and 

 generally does ; but the 

 ♦-^S^ //y/^ ' barbs and barbules are 



"^^ -v> ( ''V^v- /^>.. never connected by barbicels 



or booklets (as presently to 

 be described for ordinary 

 feathers), and therefore this 

 supplementary feather is of 

 a fluffy or downy texture, 

 not close-webbed. The ap- 

 pearance of double feathers 

 in the Emeu and some other 

 ratite birds results from the 

 equal size of the aftershaft 

 and main shaft; the former 



is well developed though inconspicuous in Parrots, 

 Gulls, Herons, and most raptorial birds ; it is small 

 and very weak in the great Passine series, in most 

 waders, and many Galliue birds ; still smaller in or 

 absent from the Duck tribe, in Totipalmate birds, 

 in some Picarians, in Owls, Pigeons, and the Os- 

 triches and Kiwis. More detailed notice of presence 

 or absence of aftershafts will be found under heads 

 of the groups of birds treated in this work. 



(3) Each web, vaue, or vexillum (Lat. vexillum, a standard: \)\. vexilla) consists of a 

 series of parallel, mutually appressed, flat, narrowly linear or lance-liuear laminae or plates, 

 eacli one of which is set by its end obliquely on the rhachis (or on the hyporhachis, as the case 

 may be), diverging at a varying open angle, and ending in a free point. Every such narrow 

 flat plate constitutes a 



(4) Barb or ramus of the vane (Lat. barba, a beard; ramus, a branch; pi. rami). 

 The barbs may be likened to the blades of a pocket knife, with the sharp edge turned toward 

 the under side of the feather, the blunt back of the blade turned to the other side. Barbs of 

 the outer webs of many feathers are deeper, stronger, and shorter than those of inner webs, 

 and commonly set on the rhachis at a more acute angle ; this difference is best marked on large 

 feathers of the wings and tail. The number of barbs to a vane is very variable ; there may be 

 several hundred. Now, if these barbs simply lay alongside one another, like leaves of a book, 



Fig. 20. — Two barbs, 

 a, a, of a vane, bearing an- 

 terior, b, b, and posterior, 

 c, barbules ; enlarged ; after 

 Nitzsch. 



Fig. 19. — A partly pennaceous, partly plum- 

 ulaceous feather, from Argus i)bea8ant; after 

 Nitzsch. ad, main stem ; (I, calamus ; a, rliachis ; 

 c, c, c, vanes, cut away on left side in order not 

 to interfere with b, the after-shaft, the whole of 

 the right vane of which is likewise cut away. 



