I. THE ROBIN. 33 



not time to-day to enter on any discuEsion of 

 the r€ason for it, which will appear when we 

 examine the placing of the wing feathers for 

 tlieir stroke. 



Now, I hope you are getting accustomed 

 to the general method in which I give you 

 the analysis of all forms — leaf, or feather, 

 or shell, or limb. First, the plan ; then the 

 profile ; then the cross-section. 



I „take next, the profile of my feather 

 (b, Fig. i), and find that it is twisted as 

 the sail of a windmill is, but more distinctly, 

 so that you can always see the upper surface 

 of the feather at its root, and the under at its 

 end. Every primary wing-feather, in the fine 

 flyers, is thus twisted ; and is best described 

 as a sail striking with the power of a scymitar, 

 but with the flat instead of the edge. 



32. Further, you remember that on the 

 edges of the broad side of feathers you find 

 always a series of undulations, irregularly 

 sequent, and lapping over each other like 

 waves on sand. You might at first imagine 

 that this appearance was owing to a slight 

 ruffling or disorder of the filaments ; but 

 it is entirely normal, and, I doubt not, so 



