V ° 1 i906 CI11 ] Dwight, The White-winged Gulls. 43 



cies, I have at least shown the way to complete success. To call 

 a plumage merely "immature" is to confess we do not know much 

 about it. Each of the species under consideration has no less 

 than five plumages that may be called "immature," the juvenal, 

 the first winter, the first nuptial, the second winter and the second 

 nuptial, and in a few exceptional cases we may add the third 

 winter and the third nuptial, making seven. Even the large 

 amount of material I have examined does not make every one 

 of these plumages perfectly clear, but it is only by the comparison 

 of comparable plumages that we shall ever arrive at the desired 

 goal. There is a large portion of Arctic America still unexplored, 

 and with other material it may some day be necessary to revise 

 in part my present conclusions. 



My work has been prosecuted at intervals during several years 

 but I trust it has lost nothing by being so long delayed. 



I am indebted to many institutions and individuals for cour- 

 tesies and for the loan of specimens, particularly to Dr. Sharpe 

 and Mr. Grant of the British Museum; to Mr. Hartert of the 

 Rothschild Museum at Tring; to Dr. Reichenow of the Berlin 

 museum; to Mr. Ridgway and Dr. Richmond of the U. S. Nat. 

 Museum; Mr. Nelson of the Biological Survey; to Dr. Allen and 

 Mr. Chapman of the American Museum of Natural History; to 

 Mr. Stone of the Philadelphia Academy of Natural Sciences; and 

 to the following private collectors, viz. Mr. O. Bangs, Mr. C. F. 

 Batchelder, Dr. L. B. Bishop, Mr. Wm. Brewster, Dr. Wm. C. 

 Braislin, Mr. R. W. Peavey, Mr. L. H. Porter, and Mr. Everett 

 Smith. 



