STRONG: DEVELOPMENT OF COLOR IN DEFINITIVE FEATHER. 151 



Passerina cyanea Linn,, Munia atricapilla Hume, and the common dove 

 have been studied ; and dry feathers from the following birds have also 

 been used : Cyanocitta cristata Linn., Sialia sialis Linn., Pitta sordida 

 Sharpe, Pitta moluccensis Swinh., Cotinga cayana Bp., and Megascops 

 asio Linn. 



I wish here to expi-ess my thanks to Messrs. Outram Bangs and J. D. 

 Sornborger for aid in procuring material. 



III. The Development of the Feather. 

 A. The Feather Germ. 



Of the many accounts of the structure and development of the feather, 

 by far the most accurate and thorough is that of Davies ('89), who 

 also gave an extended review of the literature up to the time of his 

 writing. He studied the feather witli particular reference to its homol- 

 ogies with other integumentary structures, but did not consider the 

 question of color. 



According to Davies the definitive feather is always preceded by a 

 down feather, — though in some cases the latter is represented by only 

 a rudimentary structure, — and it has the same follicle and the same 

 dermal papilla or pulp as the down feather. The epidermal fundament 

 of the future definitive feather has the same cell layers as the down 

 feather, except tliat the epitrichial layer is absent. In a longitudinal sec- 

 tion of the feather germ, it is easily seen that the cylinder-cell layer, 

 the intermediate cells, and the layer of cornifying cells are continuous 

 with corresponding layers in the epidermis of the skin. 



A description of the development of color in the feather can be better 

 appreciated if it is preceded by an account of the various steps in the 

 differentiation of the barbs and barbules. The formation of the latter, 

 especially, is complicated, and must be explained before giving a de- 

 scription of the process of pigmentation. 



Davies gave a good description of the differentiation of the various 

 parts of the feather, but his account of the formation of the barbs and 

 barbules, especially of the latter, is incomplete. Moreover, his prepa- 

 rations had evident defects in preservation, which led him into some 

 errors in his description of the conditions connected with the differen- 

 tiation of the feather fundament, which I hope to correct. 



Since the portions of the feather germ near the inferior umbilicus 

 constantly present conditions which are younger than those of portions 



