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, 
WasuinetTon, D.C., April, 1887. 
