NATURAL THEOLOGY. 178 



considerable force. They thus admirably answer 

 the purposes of a wing ; for when parted by any vio- 

 lence which would have torn instead of rumpling 

 them, had they not been separate, the bird can re- 

 place them with a few strokes of his bill. 



B. This explains why we see birds often so dili- 

 gently engaged in stroking an oily substance over 

 their feathers. It probably contains something glu- 

 tinous to hold the filaments together. 



A.. We know of nothing glutinous which the 

 weather would not harden or melt. It must be some 

 mechanical contrivance ; and so it is. Between 

 every two filaments there are little hooks ; on one 

 filament curving up, and on the other, down, so as 

 to catch over and fasten together, like the latch of 

 a door. 



In the feathers of the ostrich, this apparatus is 

 wanting, and the consequence is easily seen ; the 

 filaments hang loose and form a sort of down merely, 

 well adapted for the purposes of a fan, or for an orna- 

 ment, but which would certainly have been an imper- 

 fection, had the bird, which it is not, been adapted 

 for flight. 



In the body feathers of all birds the lower filaments 

 of the feather are not clasped together, but are mere 

 furze or down. The clasps are confined to the upper 

 part of the vane. We find, upon examination, that 

 from the place where the clasps are discontinued and 

 the downy part commences, the feathers are overlap- 

 ped by the feathers behind like the shingles upon 

 a house, and that the clasps are not wanted here for 

 p 2 



