86 



Clakk, Pterylosis oj Swifts and Hummingbirds. 



("Auk 

 LJan. 



Genus unknown. 



An unidentified hummingbird (No. 23493 U. S. Nat. Mus.) 

 shows a pterylosis exactly like the others, and is mentioned here 

 simply to complete the list of those examined. 



Comparison of the two Groups. 



Before entering on a detailed comparison of the two groups 

 which we have been examining, it will set some of the facts more 

 clearlv before us if we arrange them in tabular form. 



It will readily be seen from the table and the foregoing accounts 

 of the two groups that the points of difference between swifts and 

 hummingbirds are comparatively few, and the important matter 

 to determine is whether these differences are trivial or not. These 

 points arc the presence of frontal and occipital apteria in Trochili, 

 their virtual lack of an alula, their small numjber of secondaries, 

 their very broad, diamond-shaped dorsal tract and its practical 

 union with the femorals, and their almost complete lack of ventral 

 tracts. Let us consider these points under the three following 

 heads, (1) pterylosis of head and neck; (2) pterylosis of wings; 

 (3) pterylosis of trunk and legs. 



