GENESIS OF FAULT-BARS IN FEATHERS. 36 1 



garded as the primitive avian color-markings. He further states 

 that " from these fundamental feather-bars or their secondary- 

 derivatives a multitude of specific characters have been evolved 

 by gradual modification." 



Summary. 



1. Fault-bars, or feather defects presenting five rather distinct 

 types, have been found and described. 



2. The fault-bars occur "normally" in all bird groups, in all 

 plumages, in all feather tracts, and in all individual feathers. 



3. Fault-bars can be readily produced experimentally by re- 

 duced feeding; by the feeding of the fat stain Sudan III., which 

 seems to "tie up " certain foods ; by very strong mechanical 

 crumpling sufficient to break the tissues and blood vessels ; and 

 by lowering the blood pressure with amyl nitrite. 



4. Fault-bars are produced only by such agencies as bring 

 about poorer nutritive conditions in the feather-germs. 



5. Homologues of the fault-bars are to be found in the several 

 epidermal growths of animals which reflect better and worse nu- 

 tritive conditions. Other tissues than the epidermal may be 

 found to show structural effects of rhythms of growth. 



6. The region of growth in the feather is very restricted, being 

 narrower for the barbule — less than 1.5 mm. in very large 

 feather-germs — than for the barb-producing region. 



7. The rate of growth in the feather, as compared with growth 

 elsewhere in the organism is extremely rapid, and varies within 

 wide limits. Up to a certain point the rate bears a rather definite 

 ratio to the ultimate length of the feather, being fastest in those 

 feathers which become longest. 



8. Under "starving" conditions, the rate of linear feather- 

 growth is not affected until the third or fourth day ; after this the 

 rate falls rapidly (doves). 



9. The structural relations between the various feather elements 

 and the blood are such that not all the parts are equally favorably 

 situated to obtain nutriment from the blood ; the shaft, barbs, pig- 

 ment, barbules, inner and outer sheaths occupying advantageous 

 positions in the order named. 



10. Previous results showing that the lowest (daily) tempera- 

 ture of birds occurs in the early hours of the morning (1:00 to 

 5:00 A. M.) have been confirmed. 



