STRONG: DEVELOPMENT OF COLOR IN 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 D, 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 share 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 different 
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. 
