OG 



1902 



The Development of Color in the Definitive Feather. By R. M. 



Strong. 



TABLE OF CONTENTS. 



I. Introduction . . . 

 II. Metliods and material 

 III. The development of the 

 feather . . . 



A. The feather germ 



B. The differentiation of the 



feather . . 



1. The barbules 



2. The barbicels 



3. The barb . . 



4. The rhachis . 



5. The residual cells 



6. Cornification and with- 



drawal of the feather . 



PAGE 



147 



148 



151 

 151 



156 

 156 

 157 



158 

 160 

 160 



161 



PAGE 



IV. 



V. 



The production of color in 



the feather 161 



The' pigmentation of the 



feather 163 



Tiie chemical nature of 

 feather pigments . . . 

 The origin of pigment . . 

 The distribution of pig- 

 ment in feathers . . . 

 Change of color without 



molt 



VII. Summary 176 



Bibliography 179 



A. 



B. 



C. 



VI. 



163 



164 



168 

 172 



I. Introduction. 



The more or less striking variations in color exhibited by many 

 species of birds at different seasons of the year have been a fruitful 

 theme for discussions and speculation among ornithologists. Numerous 

 cases of change of color not apparently connected with the ordinary 

 process of molt have been reported from time to time. A theory of 

 change of color without molt was the subject of a rather warm con- 

 troversy about the middle of the nineteenth century, and there has been 

 something of a revival of the discussion in the last few years. 



It has seemed to me that a solution of the problem could not bo 

 attained without a thorough consideration of the causes of color and its 

 development. 



The present work was begun in the fall of 1899 under the direction 

 of Professor E. L. Mark in the Zoological Laboratory at Harvard 

 University. I wish here to acknowledge my great indebtedness to 



VOL. XL. — NO. 3 1 



