BIRDS 



67 



ward wing stroke, on the other hand, the resistance of the 

 air is diminished since the feathers are separated more or 



Fig. 49. — Wing of Tern. (Photographed by E. R. Sanborn, N. Y. 

 Zoological Park.) 



less Uke the slats of a Venetian bhnd, thus allowing the air 

 to pass between them. 



shaft 

 Fig. 50. — Structure of a feather. 



barb 



An examination of a single feather ' shows that it consists 

 in the first place of a shaft running through its length (Fig. 

 1 See footnote, p. 66. 



