NESTLING BIRDS AND WHAT THEY TEACH 261 



developed as in the rest of the Aves {Neognathce), and is ab- 

 sorbed later instead of becoming detached. 



In the Barbets {Cyanops) and other related forms, and in 

 the Wry-necks — and probably also the Woodpeckers — the 

 " heel " is protected by a curiously roughened pad, which dis- 

 appears soon after the nestlings leave the nursery. The use 

 of this pad is not quite clear, but it will perhaps be found to be 

 present in the young of all birds which are reared in holes on 

 the bare ground, or in hollow trees, when no real nest is made. 



