126 



BRANCH VERTEBRATA. 



feathers is concave, to resist an upward pressure. On 

 the tail is a gland containing oil, with which the bird 



FIG. 218. 



Plumage of a Bird. 1, Crown. 2, Forehead. 3, Nostrils. 4, Upper mandible. 5, Lower 

 mandible. G, Throat. 7, Neck. 8, Spurious quills. 9, Occiput. 10, Ear. 11, Nape. 

 1-,', Breast. 13, Middle coverts. 14, Large coverts. 15, Belly. 16, Tibia. 17, Tarsus. 

 18, Inner toe. 19, Middle toe. 20, Outer toe. 21, Thumb. 22, Under tail-coverts. 23, Tail. 

 24, Primaries. 25, Secondaries. 20, Tertiaries. 



preens its plumage and makes it water-proof. The whole 

 plumage is renewed (molted) once, twice, or thrice a year. 

 This molting process is never simultaneous over the whole 

 body, but takes place gradually corresponding feathers 

 on both sides of the body dropping out together, and 

 usually those not contiguous ; so that the power of flight 

 is never completely lost, or the guiding function of the 

 tail entirely crippled. The normal coloration not being 

 in many instances immediately assumed after molting, 

 has often deceived, and led to the multiplication of spe- 

 cies not warranted by more extensive observation. In- 

 deed, matured plumage is often dependent upon several 



