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PHYLUM CHORDATA 



371 



barbules of the barb immediately distal to it (A). The lower edge 

 of the distal barbule is produced into minute hooldets (D) : in the 

 entire feather the booklets of each distal barbule hook over prominent 

 flanges of the proximal barbules with which it is in contact (A, B). 



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In this way the parts of the feather are so bound together that the 

 entire structure offers great resistance to the air. 



Among the contour feathers which form the main covering of the 

 Bird and have the structure just described are found filoplumes 

 (Fig. 1034, B), delicate, hair-like feathers having a long axis and a 

 few barbs, devoid of locking apparatus, at the distal end. Nestling 

 Pigeons are covered with a temporary investment of down-feathers 



