GENESIS OF FAULT-BARS IN FEATHERS. 329 



may be cited the studies of Graf 1 on leeches and of Loeb 2 on 

 fish embryos. Graf was able to show that the characteristic 

 markings of the leeches examined depend primarily upon the 

 number and arrangement of the muscles of the body-wall. Loeb 

 showed that in Fundulus embryos, markings are produced by a 

 grouping of pigment-cells around the blood-vessels. The present 

 paper is chiefly a report of observations and experiments which 

 furnish a physiological basis for what seems to be the primitive 

 color-markings of the feathers of birds. 



This research was undertaken at the suggestion of Professor 

 C. O. Whitman ; it is here a pleasure to thank him for much 

 kindness and encouragement and to acknowledge the great value 

 of his help and criticism. 



Two observations by Professor Whitman furnished the starting 

 point for these studies; first, there is in all feathers a "funda- 

 mental barring" of the whole length of the feather; second, cer- 

 tain defects (fault-bars) occasionally appear in the plumages of 

 birds reared under adverse conditions. In presenting the facts 

 which furnish a physiological basis for these two characters, it 

 seems best to consider the fault-bars first, since they furnish the 

 key to an understanding of the fundamental bar. 



The Morphology of Fault-Bars. 

 I have found five types of defects and have made it certain that 

 they all really represent the same thing. Two of these types 

 were seen and described by Strong 3 from a hybrid pigeon. 

 Duerden i has also reported one of the types described by Strong 

 as occurring in great numbers in ostriches. These defects have 

 doubtless been seen by several naturalists. Darwin came across 

 them in at least two instances. He cites 5 some variations in the 



1 Graf, Arnold, " Ueber den Ursprung des Pigments und der Zeichung bei den 

 Hirudineen," Zool. Am., XV1IL, 1895. 



2 Loeb, Jacques, "A Contribution to the Physiology of Animal Coloration," 

 Journal of Morph., Vol. VIII., 1893. 



3 Strong, R. M., "A Case of Abnormal Plumage," Biol. Bull., Vol. Ill, Novem- 

 ber, 1902. 



4 Duerden, J. E., "Bars in Ostrich Feathers," Agr. Jour., Cape of Good Hope, 

 May, 1906. 



5 Darwin, Charles, "The Variation of Animals and Plants under Domestication," 

 Vol. I., p. 267. 



