176 bulletin: museum of comparative zoology. 



reappearance of the normal color after drying was not due to any true 

 regeneration, Init to the fact that upon drying a pliysical change had 

 taken place in the pigment and that it had not been dissolved. 



When the feather is completed, the dermal pulp possesses no func- 

 tional connection with it; tl»e barbs and barbules are tlien practically 

 isolated from the vital processes of the organism and have no further 

 power of growth. 



The arguments against change of color Avithout molt through repig- 

 mentation or regeneration of pigment may be summed up as follows : 



1. Most feather pigments are too resistant to chemical reagents to 

 warrant belief in their solution and redistribution. 



2. Pigmentation of the featlier has been observed to take place only 

 in the younger stages of the feather germ. 



3. At the end of cornification melanin granules have a detinite ar- 

 rangement, which is permanent, 



4. When cornification has ensued, the various elements of the feather 

 are hard, more or less solid, structures and their pigment contents are 

 effectually isolated from one another. 



5. There is no satisfactory evidence of the occurrence of repigmenta- 

 tion, and all the histological conditions render such an event highly im- 

 probable. 



VII. Summary. 



1. The intermediate cells at the base of the feather germ multiply by 

 mitosis, not all of them being derived from the cylinder-cell layer directly. 



2. The barbules are formed each from a single column of cells 

 placed end to end. These columns are arranged parallel to each other 

 and form the two lateral plates in each ridge of the feather fundament. 

 The lateral plates correspond respectively to distal and proximal sets of 

 barbules. The final form of the barbule results from a change in the 

 shape of its component cells. 



3. Each of tlie cells composing the distal half of a distal barbule may 

 send out one or two processes, the barbicels. 



4. The barbs are differentiated from cells making up the axial plate, 

 and appear later (Figs. 20, 21) than the, barbules. On tlie ventral 

 cortex of the barb is often found an asymmetrical ridge, which lias its 

 apex pointing towards the rhachis, as may be seen in a cross-section of 

 the feather germ. The epitrichium described by Haecker as covering 

 the cortex, I consider to be only an optical effect. 



5. A basal membrane composed of flattened dermal cells separates the 



