1920.] 



study of Nestling Birds. 



859 



barbs adhering to the tips of individual teleojitile barbs. 

 Both cases may occur in tlie same bird. 



In Passerine species the neossoptiles usually, though not 

 invariably, retain the form of a tuft. These tufts precede, 

 and are afterwards carried on, the tips of only a few, 

 definitely distributed, contour-feathers. In the case of the 

 Pied Wagtail figured, the down-tufts forming the ulnar 

 tract are subsequently borne on the innermost median and 

 greater wing-coverts. As these contour-feathers grow and 

 increase in length, what originally appeared to be a single 

 tract of down-tufts becomes divided into two distinctly 

 separated lines'^ (see fig. 2). 



Text-fiaure 3. 



3 A. Skylark, 2 clays old. 3 B. Iliiid part of a Skylark {Alamla arvensis), 

 about 7 days old. Note how in fig. 3 B the angle formed by the double 

 row of neossoptiles becomes more obtuse as the teleoptiles develop. 



Along the iiumeral tract the down-tufts precede, and 

 afterwards adhere to, the outeimost and hindmost scapular 

 feathers, but it is interesting to note tiiat those occurring 



* Incidentally it may be remarked that the feathers forming what 

 might be aptly termed the secondary coverts {i. e., the proximal section 

 of what are collectively known as greater coverts) grow before the 

 secondaries and at one stage of the fledgeling period exceed them in 

 length. Ticehurst and others have been deceived by this, and have stated 

 that the down-tiifts occur on the secondaries instead of secondary coverts. 

 In some species — Crows, for instance — vestigial down may be detected 

 on the remiges, but this is so minute and degenerate that it has been 

 ignored in most of the accompanying figures. 



