iv PREFACE TO THE THIRD EDITION. 



care. Better throw the instrument away than use it to slice species so thin that 

 it takes a microscope to perceive them. It may be assumed, as a safe rule of 

 procedure, that it is useless to divide and subdivide beyond the fair average 

 ability of ornithologists to recognize and verify the result. Named varieties of 

 birds that require to be " compared with the types " by holding them up slant- 

 wise in a good strong light, — just as the ladies match crewels in the milliner's 

 shop, — such often exist in the cabinets or in the books of their describers, but 

 seldom in the woods and fields. 



E. C. 



Smithsonian Institution, 



Washington, D.C, April, 1SS7. 



