STRUCTURE OF BIRDS. 



83 



of tlie Rasores, Fig. 28, there are various orradations. The 

 primary and secondary quills vary greatly in form, but the 

 former are almost always narrower than the latter. 



The tail, by which is here meant the feathers of that organ, 

 may be extremely short, short, moderate, long, extremelv long, 



Fig. 31. Finch. 



Fig. 32. Black Martin, 



Fig. 30. Tail ofDvvc 



and of all intermediate gradations ; even, Fig. 30 ; rounded, 

 graduated, or wedge-shaped, Fig. 33, at the end ; tapering, 

 pointed, emarginate. Fig. 31 ; or forked, 

 Fig. 32. The number of its quills varies 

 from eight to twenty or more, although in 

 by far the greater proportion of birds it is 

 twelve. 



The tints or varieties of colour presented 

 by the plumage are almost endless, and 

 greatly excel in beauty those of any other 

 class of animals, although our native birds 

 are more distinguished for elegance of form, 

 than for gaudiness of attire. 



The development of the feathers takes 

 place by means of an elongated cylindrical 

 matrix consisting of a capsule, a bulb, 

 and intermediate membranes, by w^hich 

 the matter secreted by the bulb is moulded. 

 Fig. 33. Tail of Parrot. Like the foliage of trces, the plumage 

 of birds is shed and renewed annually. In many cases the 

 change takes place twice every year. The feathers being en- 

 tirely extravascular, or, when full-grown, destitute of blood- 



g2 



