78 PIGMENT. 
very minute granules, which exhibit a lively molecular motion. 
This motion may sometimes be observed even within the cells, 
so that the rest of their contents must be fluid. As it is also 
known, that the pigment-granules may sometimes be pressed out 
from the cells, no doubt can exist respecting the cellular nature 
of these bodies, formerly called pigment-globules. The wall of 
the pigment-cells exhibits a nucleus, which is already familiar to 
some observers. It may be seen in the foetal condition of the 
pigment cells of the choroid coat in mammalia, at different 
points in that of the very young feetal pig for instance, quite 
distinctly ; and it occasions the well-known white spot in the 
centre of the cells. It commonly contains one or two nucleoli. 
It sometimes happens that no pigment-granules are deposited 
around the nucleus, but that it is surrounded by a clear, trans- 
parent areola. 
Some pigment-cells undergo a most remarkable transforma- 
tion, and one which acquires an especial importance, from the 
fact that it serves as a type of formation for other more im- 
portant classes of cells. This transformation consists in the 
cells being elongated on three or more sides into hollow fibres. 
These we shall name stellated cells. It has, indeed, been 
necessary to allude to them already when treating of bone. 
The characteristic contents of the pigment-cells render them 
best adapted for an accurate examination of this type of for- 
mation. The stellated pigment-cells, known under the name 
pigment-ramifications, are best observed in the skin of the 
tadpole. They exhibit varieties in form; we select for our 
description such of them as present the longest fibres. (See plate 
II, fig. 9.) Their appearance is that of separate black spots, 
from which slender black fibres issue on different sides. The 
black spots represent the bodies of the cells filled with pigment ; 
the fibres are the prolongations of the cells filled with the 
same material. The separate pigment-granules may be dis- 
tinguished in many situations. The body of the cell, which is 
sharply defined on its exterior, sometimes presents a clearer 
spot of a round or oval form, through which the cell-nucleus 
glimmers, and in some few instances can be distinctly per- 
ceived with its nucleolus. The diminution of the cell in various 
directions, in order to pass over into a fibre, is so gradual that 
there is no defined limit between them. The fibres pass be- 
