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 like the slats of a Venetian blind, thus allowing the air 

 to pass between them. 



shaft 

 FIG. 50. Structure of a feather. 



barb 



An examination of a single feather l shows that it consists 

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

 1 See footnote, p. 66. 



