STKONG: development of color IX DEFINITIVE FEATHEK. 177 



epidermis of the feather germ from the pulp. This was seen by 

 Studer, but apparently overlooked by Davies. 



6. The cylinder-cell layer comprises cells having the characteristic 

 cylindrical form, except in the region where there is an extensive 

 growth of the intermediate cells which go to form the barbules. 



7. The initiative in the differentiation of " ridges " is taken by the 

 intermediate cells, not by the cylinder-cell layer, nor by the dermis. 



.8. The condition of asymmetry with reference to the rhachis in 

 the vane of the completed feather is represented in a cross-section of the 

 feather germ by an unequal number of ridges on the two sides of the 

 rhachis. 



9. The " Langsfurchen " described by Davies as occurring between 

 successive ridges, and also within the ridges themselves, are artificial 

 clefts due to imperfect fixation. 



■ 10. The longitudinal extension of the feather germ is accomplished 

 by proliferation of cells at its base and also by the growth of the cells 

 composing the feather fundament. 



11. The columns of cells composing barbules experience bendings in 

 two directions, resulting in a slightly spiral course. (1) By the growth 

 of its component cells the barbule column increases greatly in length. 

 Lateral extension in the feather germ being prevented by the confining 

 sheath, its more distal portions are bent inwards until they come to 

 lie nearly parallel with the long axis of the feather germ. (2) During 

 the development of the feather the ridges become larger near their 

 attachment to the rhachis. At a given level, as may be seen in cross- 

 sections, this results in a crowding or lateral displacement of ridges 

 towards the ventral side of the feather germ. The lateral plates (com- 

 posed of barbule columns) are bent so that they present a concave face 

 towards the rhachis. This condition is represented in a cross-section by 

 the curving of the roivs of barbule cells. 



12. While a deposit of melanin pigment in the more central of the 

 medullary cells of the barb is usually associated with the production of 

 blue, as described by Haecker, the pigment may occur in the barbules 

 and not in the barbs. This is the case in the indigo bunting (Passerina 

 cyanea). 



13. The melanins are supplied to the feather by branching pig- 

 ment cells, which distribute their pigment rods to cei'tain cells of the 

 feather fundament during, or immediately preceding, early stages of 

 cornificatiou. 



14. The granules of melanin found in feathers are formed in the cyto- 



VOL. XL. — NO. 3. 3 



