FOEM AND HABIT: THE WING. 



lY 



organs we sliall direct our attention to their external form 

 rather than their internal structure. 



The Wing. — Birds' wings are primarily organs of 

 locomotion, but they are also used as weapons, as musical 

 instruments, in expressing emotion, and they are some- 



FiG. 4.— Young Hoatzin, showing use of hooked fingers in climbing. 



Lucas.) 



(After 



times the seat of sexual adornment. As an organ of loco- 

 motion the wing's most primitve use is doubtless for 

 climbing. Gallinules, for instance, have a small spur on 

 the wrist or " bend of the wing," and the young birds 

 use it to assist their progress among the reeds. A more 

 striking instance of this nature is shown by that singular 

 South American bird, the Hoatzin {O^isihocomus cris- 

 3 



