96 



Geiieral Notes. I Jan. 



thing; this at least is mj own view, and no better example could be 

 brought forward to sustain it than that of the Hummingbirds which 

 Mr. Clark cites as examples of the primitive pattern of pterjlosis. Some 

 years ago I wrote: " The pterjlosis of all birds is more or less adaptive, 

 having some direct relation to their habits, and this adaptation is well 

 shown in hummingbirds. The bare tracts on the nape and along the 

 throat allow the neck to readily lie against the middle of the back, or to 

 bend downward over the point of the bi-east bone, while the bare spaces 

 under the wing and along the sides of the body permit the wings to be 

 easily closed and applied to the body, the side spaces conforming almost 

 exactly to the curve of the edge of the folded wing. The large bare 

 space on the under side, found in nearly all birds save water fowl, is 

 mainly to allow the warmth of the body to be directly applied to the eggs 

 during incubation, and in birds like ducks and penguins (also auks) 

 which are densely or completely feathered beneath, a bare spot is present 

 during the breeding season." Thus the pterylosis of the hummingbird 

 is primitive because it shows few or no modifications of its purely adap- 

 tive features. 



It is interesting to note that the pterylosis of the great struthious birds 

 bears out the two theories that these birds are descended from ancestral 

 forms which ilew, and that the apteria are due to mechanical causes. For 

 while it is commonly stated that these birds are evenly covered with 

 feathers, yet, according to that careful observer, Mr. Pycraft, they have 

 well-defined, if small, apteria, and these bare places are best defined in 

 Rhea, the genus which has the largest wings. 



Finally, while hoping that Mr. Clark may continue those careful 

 pterylographical studies which are yielding such good results, and grant- 

 ing the great value of the pterylosis as an aid to classification, I must con- 

 fess that it seems rank heresy to hold that primary, fundamental struc- 

 tural characters are more susceptible to modification than are secondary 

 external characters. — F. A. Lucas, Washington, D. C. 



