76 DWIGHT 



plumage an assemblage of feathers produced by one or more 

 moults ; and the underlying principles or laws by which every 

 moult and every plumage ma)^ be explained are the following : 



1. Every species has a definite series of plumages and moults. 



2. Moult is periodical feather growth. 



3. Moult is complete or incomplete. 



4. Moult is modified by age, sex and individual. 



5. Plumage is renewed by moult. 



6. Plumage is modified by wear. 



This is the whole matter in a nutshell — no " undiscovered law 

 of nature," no "restoration," no "rejuvenation" of feathers, ho 

 " repigmentation," in fact, no " aptosochromatism," what is left 

 of it being represented by the good Anglo-Saxon word wear. 

 The only question to ask in order to solve a plumage is : When 

 did each feather grow ? Could anything be simpler ? Every 

 feather develops with a definite color and pattern which it re- 

 tains modified only by w^ear until the next moult. This is the 

 A B C of it and only those ignorant of facts can maintain the 

 contrary, and assert that a feather once grown can rebuild or re- 

 color itself. A mature feather is acknowledged by physiologists 

 (and by e\'er},'one except those with theories) to be a completed 

 appendage of the skin, cut off from vital connection \\ith the 

 body and incapable of any but destructive changes. I shall 

 show that regenerative processes occur only by moult in some 

 of the very species that have been exploited as undoubted ex- 

 amples of abnormal color change without moult, and I hope to 

 protect other species that as yet have escaped the imputation. 

 The highroad to such conclusions is not an easy one to travel, 

 but those who will begin at the beginning and follow me will 

 find it everywhere avoiding the pitfalls of doubt, that end in blind 

 theories, and leading straight to an understanding of the signifi- 

 cance of plumage. 



Determination of Age by Osteological Characters 



One of the first essentials in the stud}' of moult, and one 

 hitherto almost wholly disregarded, is the ability to distinguish an 



