1 2 PTERYLOGRAPIIY. 



CHAPTER II. 

 OF THE PRINCIPAL FORMS OF FEATHERS. 



THE feathers of birds, and especially their barbnles, exhibit a great number of different 

 modes of structure. Nevertheless, one form passes into another, and not unfrequently several 

 forms are found combined in the same feathers, and even in the same parts. For this reason I 

 do not intend, nor indeed, is it possible, to give a complete discrimination and definition of the 

 forms of feathers. However, I consider the definite indication of some of the chief forms to be 

 necessary, and I distinguish three of them under the names of PENNACEOUS (pennaced), DOWNY 

 (plumulaced), and FILOPLUMOUS (jiloplumacea). 



1. The pennaceom structure is recognised by its complete and strong stem, parenchy- 

 matous shaft, rigid barbs and barbules, and by the compressed, or, as in the case of metallic and 

 irridescent feathers, flattened form of the barbules, the anterior rows of which usually possess 

 barbicels and hooklets. 



2. The downy structure is produced when the stem is weak and short, and the shaft (where 

 it occurs) and barbs remain soft ; the barbules are very fine, very mobile, and commonly very 

 long, but compressed only at the base, and afterwards round and filiform. With this the above- 

 mentioned interrupted dilatation into dark knots with two points, and a complete deficiency of 

 hooklets is always combined. 1 



3. The filoplumous structure is distinguished from the two others by a very thin, rigid stem, 

 usually a translucent shaft in which the pith is wanting, very fine, rigid, round barbs, and 

 short, somewhat rigid, fiiliform barbules. Neither hooklets nor knots occur in this form. 



CHAPTER III. 



OF THE DIFFERENT KINDS OF FEATHERS. 



ALTHOUGH the four kinds of feathers formed upon the primary types above described cannot 

 be separated by any determinate boundaries, I believe that only these four can be admitted. I 

 have endeavoured to distinguish them by the names of CONTOUR-FEATHERS or SURFACE-FEATHKRS 



1 See my observations on the variegation of the downy plumage, in VOIGT'S ' Magazin fur den 

 neuest. Zustand der Naturkunde/ Band xi, p. 393, tab. vi, 1866. 



