APPENDICES OF THE SKIN. 93 
general slightly convex ; the inner nearly flat, with a groove 
in the middle; and the whole tapering 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 taperimg 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 durmg 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 determme 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. 
