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THE AMERICAN NATURALIST [Vol. XLII 



mented, although the difference in this respect between "fault- 

 bars" and "fundamental bars" is not marked, but results in 

 the melanin pigment being "laid down in alternating light and 

 dark transverse bars. ' ' 



Among the results summarized by the author as confirmed by 

 or resting upon these investigations may be mentioned: The 

 occurrence of fault-bars normally in all birds and in all feathers ; 

 they can also be produced experimentally. A daily blood-pres- 

 sure rhythm with a minimum pressure between 1 and 5 A.M. 

 "The reduced nutrition brought about daily by this minimum 

 blood-pressure; the disadvantageous position, in relation to the 

 blood, of the pigment and barbule elements of the feather; to- 

 gether with the very rapid rate at which feathers grow, furnish 

 the complex of conditions which bring unfailingly into existence 

 a fault-bar, and to a more or less appreciable extent a light 

 fundamental bar, at perfectly regular intervals in the entire 

 length of every feather formation." "The melanin pigment of 

 the feathers of birds shows, under favorable conditions, quanti- 

 tative variations of the pigment produced in response to changes 

 in the available food supply. This is an additional evidence 

 that this pigment is not a derivative of haemoglobin, but of the 

 serum or cell proteids." "These results furnish a description, 

 in the terms of physiology, of the mechanism of the 'inheritance' 

 of certain fundamental color-characters of all birds." "The 

 fundamental bars furnish the starling point for all evolutionary 

 studies on the color-characters of birds." 



These investigations may well serve as the foundation for 

 researches upon the color-characters of birds, but whether they 

 are to throw much light upon the genesis of color patterns in 

 plumage remains for the future to disclose. It may be noted 

 that no reference is made in this connection to the cause of dif- 

 ferentiation of feather structure, treated by the author in a 

 former paper. J. A. A. 



HERPETOLOGY 



Ruthven's Variations and Genetic Relationships of the Garter- 



