MUSEUM OF COMPARATIVE ZOOLOGY. 221 



than in the transverse direction, and sometimes the reverse, thus 

 giving in some cases a deep, narrow bill, and in others a broad, de- 

 pressed bill. In the latter case the differences are especially important, 

 as will be more fully shown later. In regard to the tooth-like inden- 

 tation near the tip of the bill in so many of the insectivorous birds, it is 

 found that in some species which usually have it strongly developed, 

 specimens occasionally occur with the indentation nearly or quite obso- 

 lete. Again in other cases where this feature is usually but slightly 

 developed, some specimens have the notch at the tip of the bill exceed- 

 ingly prominent. Similar variations occur in regard to the develop- 

 ment of the so-called " festoon " of the upper mandible in the hawks, 

 as Dr. Bryant has already sufficiently shown. 



The greatest range of individual differentiation in any given organ 

 occurs, as would be naturally expected, in those species which have that 

 organ more than ordinarily developed, and also in species of a low 

 grade of structure. In the long-billed Grallce both these conditions 

 exist, and it is in such genera as Numenius, Gambetta, Limosa, Scolo- 

 pax, Philohela, and Gallinago, that the maximum of bill variation is 

 seen. It is less marked in the song-birds, though in many members of 

 this group the variation is by no means small. In the typical wood- 

 peckers, on the other hand, which have the bill especially adapted to a 

 peculiar function, that of digging into wood, the variation is scarcely 

 appreciable, since any considerable variation from its usual form would 

 seriou-dy impair its efficiency. In the semi-frugivorous and terrestrial 

 Picidcc, however, we again meet with the usual range of variation. 



In the accompanying plates illustrative of variation in the bill, 

 representatives from the higher types of the Oscines have mainly been 

 chosen, several representatives from widely different families having 

 been selected. Plate IV, figures 1 and la, 2 and 2a, give a view of 

 the bills of two specimens of the common king-bird [Tyrannus caro- 

 linensis), from Eastern Massachusetts, which differ from each other as 

 much as the bills of different genera sometimes do. One of them, as 

 will be seen, is so much narrower and deeper than the other as to give 

 very different proportions and outlines. The skulls of these two speci- 

 mens vary in the same manner as do the bills, the one having ;i broad, 

 flat skull, and the other a narrow, high one. Two specimens of M>/iar- 

 chus crinitus, one of which is from South Carolina and the other from 

 Western New York, differ as much from each other, and in nearly the 



