GENESIS OF FAULT-BARS IN FEATHERS. 355 



black. Quantitative estimates by this method are therefore not 

 easy. Pis. XII., Fig. 4, and XV., Fig. 26, and text Fig. 2 show, 

 very clearly that in these two types of fault-bar there was practi- 

 cally a suspension of pigment production during the fault-bar 

 producing period. 



In PI. XIII., Fig. 14, is shown a feather from a Japanese turtle 

 dove. Here a continued reduction of the pigmentation of nearly 

 all of the primaries followed a period of malnutrition. This period 

 is indicated in the primaries by a narrowing of the feather-vane 

 at one point and by a few fault-bars. The rectrices of the same 

 bird, recorded this starving period by means of a few very ob- 

 vious defects. (The actual starving of this bird was neither in- 

 tended nor observed, but this interpretation seems unquestionable). 

 In other cases it has been observed that a very strong fault-bar 

 sharply separates a pigmented part of a feather from an unpig- 

 mented part. PI. XIII., Fig. 10, shows such feathers from a 

 pigeon. The part of the feather proximal to the defects is unpig- 

 mented, although it normally bears pigment. 



The observation that fault-bar producing conditions may occa- 

 sionally weaken or apparently permanently destroy the pigment- 

 producing power of the feather would seem to be of much 

 importance ; but the mechanism of this action is wholly unknown. 

 The fact that these fault-bars are areas provided with a reduced 

 amount of pigment, and the further fact that nutrition stands in 

 a causal relation with the fault-bars — and the reduced production 

 of pigment — suggests however some interesting relations of the 

 melanin pigment and the food. Indeed one cannot review the 

 results of these studies without finding some evidence that 

 melanin arises not from hmnaglobin but from the proteids of the 

 foods {serum) or of the cell. Recent work in physiological chem- 

 istry has furnished much evidence in favor of this view. It would 

 seem that in the birds the production of feather pigment stands in 

 a rather immediate relation to the foods, and even to fluctuations 

 in the food supply. 



In regard to the behavior of lipochrome pigments, it may be 

 said that, though a thorough study has not been made, they 

 seem to take up their positions without regard to the fault-bars and 

 fundamental bars. Where the word "pigment" is unqualified in 

 this paper, melanin is meant. 



