THE STRUCTURE OF A FEATHER 259 



THE STRUCTURE OF A FEATHER. 



Familiar as it is, there are few works of nature which 

 better repay careful study than a feather. Its adapta- 

 tion to its purpose is complete ; it is strong, light, 

 flexible and elastic ; its concave surface, which in the 

 case of a quill, is turned towards the inside of the 

 wing, or towards the under-side of the tail, catches the 

 air, while the convex surface allows the air to glide 

 past with little resistance. The feather resembles 

 a host of other natural contrivances in this, that 

 the more we study it, the greater wealth of contrivance 

 we discover. It is wonderful enough when we merely 

 hold it in the hand, and examine it by the unaided 

 eye, but a pocket-lens brings out further and more 

 interesting details, while the utmost refinements 

 are only to be appreciated by those who can com- 

 mand a good microscope and some delicacy of 

 manipulation. 



Notwithstanding the utmost diversity in detail, 

 all feathers are constructed upon a common plan. 

 We have feathers with two shafts, feathers with one 

 shaft and feathers with no shaft at all ; feathers 

 which bear a stiff and broad vane, feathers which form 

 branching plumes, waving in the gentlest current 

 of air, and feathers which at an early stage of develop- 

 ment crumble to powder. Feathers may be used for 

 warmth, for defence, for decoration, for flight. They 

 are of all colours, sizes and shapes. But there is hardly 

 any organ of the Bird's frame more uniform in its 

 early stages of grow r th. 



In the present period of the earth's history, feathers 



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