PASSERINE BIRDS OF NEW YORK 117 



and other German writers of his period ; and to have received 

 recent attention at the hands of Allen ('96), Chadbourne ('97) 

 and Chapman ('96 and '97). It is to this theory, so far as it 

 concerns Passerine species, that I now invite attention. 



In view of the endless complexity of birds' plumages and the 

 wide diversity in the manner of their acquisition demonstrable 

 even among a few Passerine species, it is not surprising that 

 theoretical explanations should flourish as long as the facts of 

 moult regarding any species are not known. To catch a bird 

 in moult is no easy matter, to catch him in all his moults is a 

 task of considerable magnitude and yet as fast as this has been 

 accomplished, theory has become superfluous. 



Theory has even gone so far as to assert new growth of 

 abraided barbs and barbules by exudations from a frayed 

 weather-beaten feather, although most writers have contented 

 themselves with alleging a fresh influx of pigment or a redistri- 

 bution of color granules. No two of the upholders of this 

 theory of so-called "color change without moult," or "aptoso- 

 chromatism," have agreed as to how a feather thai to all appear- 

 ances has been histologically dead for many months may sud- 

 denly absorb, create or redistribute fresh coloring matter and the 

 weakest point of their theory is the necessity for a new law of 

 some sort to explain the theory. The mental attitude of those 

 who believe in these changes is a curious one. They usually 

 admit that moult is responsible for the renewal of one feather 

 but claim a color change they cannot exactly explain in the 

 feather adjoining. They would have Nature work according to 

 well established laws in renewing feathers numbers i, 2 and 3 

 of a series and then adopt a new one for number 4 ! They 

 would have us believe that the shaft of a feather is a sort of an 

 avian thermometer tube up and down which coloring fluids slip 

 according to the seasonal systemic warmth of the bird ! There 

 is an element of the absurd about the position taken by theorists, 

 but it is only fair to them to sift the evidence they bring forward 

 in support of their theories. This is the evidence of live birds 

 and the evidence of dead ones. Live birds must of necessity 

 be caged birds, and dead ones of course are chiefly museum 

 or cabinet specimens. 



