Vol i^OjP n ] Clark, Pterylosis of Sivifts and Hummingbirds. 71 



turn. The femoral tracts though diffuse, are very evident, and 

 are usually long, so that they extend backward almost or quite 

 to the tail-coverts, while anteriorly they reach downward and for- 

 ward, often to the sternals and along the sides to the posterior 

 end of the numerals. The latter tracts are narrow or of moderate 

 width, passing over the humerus either at its head or near the 

 middle, and are clearly connected with the feathering on the pata- 

 gia of the wings and even with the upper cervical tract. The large 

 oil gland is almost surrounded by a small tract, chiefly made up 

 of the upper tail-coverts. 



The lower cervical tract is forked quite far forward on the neck, 

 and each half passes into a broad sternal tract which continues 

 without interruption, though becoming narrower, to the belly, 

 where it ends rather abruptly. In many swifts just at the point 

 where these pterylre leave the neck and pass on to the breast, an 

 anteriorly divergent fork of the ventral apterium nearly severs 

 them ; this is most evident in Chatura and Hemiprocne. In some 

 of the large swifts (Hemiprocne, Cypseloides) scattered feathers 

 in the region of the furculum tend to unite the anterior ends of 

 the 2 sternal tracts. There is nothing else peculiar or specially 

 noteworthy in the ventral pterylosis, but the sternals are connected 

 anteriorly over the shoulders with the humeral tracts and posteri- 

 orly, occasionally, with the femorals. 



The characteristic and important features of this pterylosis 

 may be summarized as follows: the presence of supraocular apteria, 

 an upper cervical apterium, and a long and conspicuous spinal 

 apterium, the absence of lateral cervical apteria, the large and 

 diffuse femoral tracts, and the continuity and marked develop- 

 ment of the lower cervical, sternal and ventral tracts. In addition 

 to these features, the following points are noteworthy. Aftershafts 

 are present on the contour feathers and are often very large. True 

 down feathers are wanting and filoplumes are not notably abun- 

 dant, though usually evident on the neck and the posterior part 

 of the back. The oil gland never bears a terminal tuft of feathers. 

 There are always 10 rectrices and 10 primaries. The alula con- 

 sists of 2 or 3 feathers and in some cases there is also a distinct 

 claw. The secondaries are usually 8 or 9 in number, and the 1 

 wing quincubital, but in Cypseloides, Hemiprocne and Macrop- 



