APPENDICES OF THE SKIX. 93 



general slightly convex ; the inner nearly flat, with a groove 

 in the middle; and the whole tnpering to a point at the 

 distal extremity. It is generally single in the large feathers 

 of the wing and tail of birds, but frequently double in the 

 feathers on the body. 



The web usually occupies both sides of the shaft, and 

 consists of the barbs, which are flattened tapering slips of 

 matter, similar to the shaft, placed transversely, adhering 

 thereto by their base, and lying over each other, like the 

 leaves of a book, pointing outwards. The sides of each 

 barb are furnished with barbules, in the same manner as 

 the shaft is decorated with barbs. 



Feathers exhibit very remarkable differences with regard 

 to colour. The shaft is frequently of one colour, while the 

 webs are of another ; and different parts of the same web 

 may even be observed exhibiting dissimilar tints. The co- 

 lour of the feathers of some birds, appears to vary with the 

 season, always becoming of a paler hue during the cold of 

 winter. Particular kinds of nourishing food likewise effect 

 similar changes ; but the colours, in this case, become 

 deeper. The feathers of several birds, after death, lose 

 their lustre, and frequently become paler in the colour. 

 Thus the orange-coloured white of the belly of the com- 

 mon merganser soon fades after death. These circum- 

 stances point out the vitality of this appendix, however 

 difficult it may be to determine the manner of circulation 

 of any fluid, between the parts of the fully formed feather 

 and the body. 



Feathers, like hairs, are not only renewed periodically, 

 but they are readily reproduced, if accidentally destroyed. 

 The manner in which they are formed, is variously stated 

 by different authors, few of whom appear to have examined 

 the subject with any degree of attention. The following 

 'account is given as the result of personal observation. 



