Aftershafl of certain Birds. 21 



"double feather There are^ however^ a great many 



birds in which it is deficient,, and in its place a few isolated 

 barbs occur." 



Dr. Rochebrune, on the contrary, states of the aftershaft : — 

 '' La plume adventicCj variable dans ses formes, ses dimensions, 

 sa composition, n'est pas toujours unique ; tres souvent on en 

 rencontre deux ou un plus grand norabre, distinctes, inde- 

 pendantes les unes des autres, quoique en connexion par leur 

 insertion sur la tige de la plume principale. Ce mode d^in- 

 sertion n^'est pas non plus invariablement fixe ; on voit ces 

 plumes adherer tantot directement a la face inferieure de la 

 tige principale, tantot en cote, soit au niveau de la cavite 

 orabilicale citec par Nitzsch, soit en-dessus ou en-dessous, 

 etre sessiles ou pedicellees, posees en couronne etc., enfin 

 dans aucun cas et sous aucun rapport, elles ne ressemblent ^ 

 la plume principale," 



The main difference therefore between the two definitions 

 appears to be that the aftershaft, according to Dr. Roche- 

 brune, is not always single, but that there are frequently 

 several distinct and separate aftershafts present on the same 

 feather. This may be true ; but the facts brought forward 

 by Dr. Rochebrune, so far as I have been able to verify 

 them by comparison with the feathers themselves and even 

 with his own figures, do not appear to confirm this statement. 

 To take an instance ; the aftershaft of Numida is described 

 by Dr. Rochebrune in the following words: — "On trouve cinq 

 plumes adventices distinctes, d^inegale longueur, sessiles sur 

 la tige principale et a insertion commune ; leurs barbules sont 

 assez fortes, courtes et mediocrementrigides." A figure {op. 

 cit. pi. iii. fig. 1) is given o£ one of the feathers of this bird, 

 which is a sufficiently accurate representation of the original. 

 The aftershaft consists of a short stem bearing on either side 

 two or three barbs, each of which Dr. Rochebrune, if I under- 

 stand him rightly, considers to be the equivalent of a single 

 aftershaft, such as that which is stated to be found in Perdix. 

 It does not appear to me, however, that tliis comparisou is 

 at all justifiable; the barbs of the aftershafts are entirely 

 similar to those which spring from the lower portion of the 



