strong: development of color IX DEFINITIVE FEATHER. 167 



the number of cells of each group found at the indicated distances 

 from the basement membrane. 



The measurements given in this table show that there is no no- 

 ticeable correlation between the position of pigment cells and their stages 

 of development. Moreover in stages later than those of Group Z), the 

 pigment cells come to occupy a position very close to the pulp, seeming 

 in some cases to migrate towards rather than away from it. 



It would be absurd to deny all physiological relation whatever of the 

 melanins to the blood, since the whole feather germ is of course depend- 

 ent on the blood for nourishment. 



I have observed that the nuclei of pigment cells lose stainable chro- 

 matin, as described by Jarisch ('92), and it is only reasonable to sup- 

 pose that the nucleus must sliare to some extent in the profound 

 changes that take place in the pigment cell. The first visible pigment 

 elements appear, however, in the cytoplasm, and it seems probable that 

 the pigment rods are formed from cytoplasmic material. 



Against the hypothesis that pigment is an excretion product, may be 

 urged the striking variations in amount of pigmentation for djfferent 

 animals, where there is no reason to believe that corresponding differ- 

 ences in excretion occur. Albinos lack entirely melanin pigmentation 

 in integumentary structures, yet no one would deny that they have 

 normal excretory processes. Then, too, such a theory requires, as Kru- 

 kenberg ('84) has said, a marvellous selective power on the part of the 

 pigment cells, and it is more difficult to conceive of this than it is to 

 imagine that certain cells manufacture from a common nourishing 

 material the pigment granules that are to be supplied to neighboring 

 cells. 



