178 BULLETIN : MUSEUM OF COMPARATIVE ZOOLOGY. 



])lasm of so-called pigment cells. These are differentiated exclusively 

 from epidermal cells which lie in the intermediate cell layer of the epi- 

 dermis of the feather near the apices of the epidermal ridges. 



15. Before cornification has ceased, all the pigment wliich the feather 

 is ever to receive has been supplied to the cells composing its fundament. 



16. Changes in the color of plumage may take place either (1) by a 

 molt, during which the new feathers may have the same pigmentation 

 as tlieir predecessors or a different one ; (2) by a loss of certain portions 

 of the feather ; or (3) by physical disintegration in the cortex of the 

 feather as the residt of exposure. There is no satisfactory evidence of a 

 process of repigmentation, and the histological conditions of the feather 

 render such a process highly improbable. 



1 wish to express my sincere gratitude to Professors IMark and G, H. 

 Parker for helpful criticism and revision of the manuscript. 



