7() Clark, Pterylosis of Swifts and Hummingbirds. |_Jan 



Cypseli. 



The general pterylosis of the swifts is very distinctive and re- 

 markably uniform, so that the figures of Chcetura pelagica (Plate 

 II) will answer with slight changes for any of the other species. 

 The tracts are all clearly defined and well feathered, while the 

 apteria are uniformly naked. The forehead is quite thickly feath- 

 ered, but with large crescent-shaped apteria over the eyes, while 

 the crown and occiput are rather sparsely feathered, in longitu- 

 dinal rows. The throat is fully feathered but there are apteria 

 along the rami of the lower jaw. The upper cervical tract is very 

 broad, and unites along the sides of the neck with the lower cervi- 

 cal tract, so that there are no lateral cervical apteria. Between 

 the shoulders, it bifurcates to form the dorsal tract. On the ante- 

 rior part of the neck, close to the head, is a large and very evident 

 apterium, one of the most characteristic features of the pterylosis. 

 It is a very curious fact that Shufeldt ('88 and :02) positively denies 

 the existence of this apterium in the swifts, while Lucas ('92) states 

 that "some of the swifts" possess it, and Thompson (:01) makes 

 no reference to it in his description of Collocalia, though his figure 

 shows an entire absence of feathers on the anterior dorsal part of 

 the neck. A careful reexamination of my material, figures and 

 notes, leaves no doubt whatever of the existence of this apterium 

 in every species of swift examined. I can only account for Shu- 

 feldt's statements by supposing that they are based on his exami- 

 nation of Chcetura pelagica and Aeronautes melanoleucus: in Chce- 

 tura this apterium is not very large, while in Aeronautes it is smaller 

 than in any other swift. It is not inexplicable therefore that it 

 was overlooked in these cases, but it is hard to see how it could have 

 been overlooked in Cypseloides, which he also examined. — The 

 dorsal tract is divided from the shoulders to the middle of the 

 sacrum, by another long but narrow apterium, into two narrow 

 bands of nearly uniform width, but it ends* in a single narrow band 

 at the base of the oil gland. The anterior portion of the space 

 between the dorsal and humeral tracts is sometimes separated 

 from the rest so as to form a small but quite distinct apterium on 

 each side of the upper cervical tract. This is well shown in Chce- 



