OF THE GENERAL DIFFERENCES OF THE FEATHER-TRACTS. 19 



plumage, which must never be omitted, an inspection of the inner surface of the skin is generally 

 sufficient, and, indeed, this must always suffice when we can only obtain skins intended to be 

 stuffed for collections. If I had not employed this third method, I should have found some 

 difficulty in studying the arrangement of the feathers upon so many genera and species, some of 

 them of great rarity. 1 



CHAPTER IV. 

 OF THE DIFFERENCES IN THE GENERAL DESIGN OF THE FEATHER-TRACTS. 



IN the design of the feather-tracts I have noticed two chief differences, namely, densely- 

 feathered tracts (dcnsipennte), as I may call them for the sake of brevity, or those in which the 

 feathers stand close together, and scantily-feathered tracts (raripenna}, in which the feathers are 

 more scattered and separated by greater intervals. Besides the contour-feathers, the tracts 

 always contain filoplumes, and here and there also some semiplumes, especially at their margins- 

 True down-feathers are wanting in the feather-tracts of all the groups characterised by me as 

 air-birds and ground-birds, but in the water-birds they always occur between every four contour- 

 feathers of the tracts; sometimes one, sometimes more (see ante p. 13). Other differences of 

 the feather-tracts may be indicated by the following terms : strong, when the contour-feathers 

 have very thick tubes ; weak or stunted, when the contour-feathers are small and insignificant. 

 The tracts usually appear very distinct when they are circumscribed by a definite boundary, 

 consist of strong feathers, and are margined by naked or merely downy spaces. Sometimes, 

 however, they dwindle away towards the margin, and lose themselves as weak tracts in the neigh- 

 bouring spaces, which then bear strong down-feathers or even semiplumes. By this arrange- 

 ment, which I have met with in Buceros and Colius, the interrupted plumage passes into the 

 continuous form. 



The feather-tracts also vary greatly in their breadth; in some birds, such as Galbula, 

 Merops, Upupa, and Ardea (see Plates IV and VIII), they are extraordinarily narrow, in 

 others, on the contrary, moderately broad, but with the spaces reduced in the same proportion. 

 This kind of plumage, as it occurs, for example, in the Steganopodes and Unguirostres (Plate X), 



1 I have made observations as above described, not only in Halle, but also in the far richer 

 museums at Berlin, Frankfurt-on-the-Maine, Leyden, Paris, and Geneva, the treasures of which were 

 placed at my disposal by the great kindness of their chief authorities, MM. Lichtenstein, Cretschmar, 

 Temmiuck, the two Cuviers, and the two Geoffroys. I was also greatly assisted by the distinguished 

 artists, to whose talents and industry these collections are indebted for a great part of their lustre, 

 namely, M. Rammelsberg, at Berlin ; MM. Florence Prevost, Perrot and Bibron, at Paris ; and 

 M. Linder, at Geneva. All of these gentlemen have rendered me particular services in this depart- 

 ment of my studies. 



