Aves. in 



the wing. What effect does this have on the individual feathers 

 and the wing as a whole? 



7. Repeat the experiment with the outer surface of the wing, 

 noting carefully how each separate feather is acted on, and what 

 is the effect on the wing itself. What is the effect of the wing on 

 the air current in each of these experiments ? 



THE FEATHERS. 



i . Pull out one of the large wing quills and study its parts ; 

 the central axis is the shaft ; the expanded part is the vane ; the 

 side branches of the shaft are the barbs, and the side branches 

 of the barbs are the barbules. With a lens examine the upper and 

 lower surfaces of the vane ; then tear one of the barbs loose from 

 the barbs in front of and behind it, and study it carefully ; again 

 watch closely while tearing two barbs apart, to see how the barbules 

 are related to each other; now examine the vane of the same 

 quill at the very beginning of the vane, near the end that was 

 attached to the wing. What is the difference between the arrange- 

 ment of the barbs in these two places? Observe the hole in 

 the tip of the shaft ; run the point of a dissecting-needle along the 

 groove in the under surface of the shaft toward the base of the 

 shaft. This should lead the point of the needle into another 

 opening, communicating with the cavity of the shaft. Examine 

 this region with a lens, and determine that the' two sides of the 

 vane meet at this point. Make drawings of a quill, as seen from 

 above and below, showing all these points. 



With sharp scissors cut across the feather in the middle of the 

 vane. Look at the cut end ; observe that the vane is attached to 

 the upper edges of the shaft ; compare the place of attachment 

 of the vane to the shaft, with the place of attachment of the wing 

 to the body. Cut part of the wider side of the vane at right angles 

 to the barbs ; with a lens, or a low power of the microscope, 

 examine the edge of this cut. Make drawings showing these 

 arrangements of the parts of the quill. What are the advantages 

 of such arrangement? 



