330 University of California Publications in Zoology [Vol. 11 



INTRODUCTION 



As preliminary to a stud.y of the modifications and evolution of 

 feathers in the various orders and families of birds, it seemed 

 desirable to ascertain the range of variation and degrees of 

 development displayed in the plumage of a single bird. In the 

 selection of a species to use for this purpose, it was decided to 

 employ one which would show as great a number as possible of 

 ordinary types of feather modification. A brief survey of the 

 available birds to use for this study showed that of all North 

 American birds the Marsh Hawk, Circus hudsonius (Linnaeus), 

 combined the greatest number of ordinary feather types. It 

 possesses strong and highly developed flight feathers, well- 

 developed tail feathers, body feathers with aftershafts, rictal 

 bristles, eyelashes, ear-coverts, facial ruff, an oil-gland tuft, 

 powder-down patches, ordinary doMTi, and filoplumes. 



The specimen used for the greater part of the work is number 

 11942 of the University of California Museum of Vertebrate 

 Zoology. It is an adult female, taken at Riverside, California, 

 November 2, 1887. 



The most superficial glance at such a bird is sufficient to show 

 that there is a very great difference in the structure of its 

 various kinds of feathers. The stiff, strong flight feathers are 

 not less unlike the soft, fluffy belly feathers than are these unlike 

 the hairlike bristles about the mouth and eyes. Indeed it may 

 be stated that nowhere in the vertebrate phylum can a greater 

 diversity of integumentary structures be found on a single indi- 

 vidual than on such a bird. That such a variety of structures, 

 varying as widely in function as in form, should be reducible 

 to a single type of integumentary growth, similar in origin, 

 development, and fundamental structure, is truly remarkable. 



A study of the modifications which are involved in producing 

 this variety of form, and the extent of these modifications in 

 feathers of various parts of a single bird's body, is the ob.jeet of 

 the present paper. I\Iost grateful acknowledgments are here ex- 

 tended to Professor C. A. Kofoid, of the University of California, 

 for his kindly aid and supervision, and to Dr. Joseph Grinnell, 

 of the Museum of Vertebrate Zoology of the University of Cali- 

 fornia, for his generous co-operation in the supply of material. 



