378 J. M. D. OLMSTED 
have evidently made their way into the bud from an outside 
source. These included cells may be classified under two main 
types occurring in approximately equal numbers. The first is 
a very small cell which appears as a naked nucleus with a very 
pronounced nucleolus (fig. 3, a). This type of cell seems to be 
identical with the small leucocyte occurring normally in the blood. 
Under favorable conditions, e.g., in blood smears, in sections of 
blood-vessels, and in clear spaces between cells of the epidermis, 
one can see a small amount of faintly staining cytoplasm sur- 
rounding the nucleus. The clear area which often appears in 
tissue surrounding the cell is apparently due to the dissolving 
away of the protoplasm of the cells which are in contact with 
it (fig. 3, b). The other type of included cell is larger than the 
first and further distinguished from it by having a varying accumu- 
lation of brown pigment granules (fig. 2, b, c). This pigment 
is exactly similar to that seen in the irregularly branching chroma- 
tophores scattered throughout both epidermis and dermis (fig. 
2, d), though in the ordinary chromatophore the granules are 
often so dense as to form a homogeneous black mass. The 
wandering pigment cells in buds fixed in fluids containing osmic 
acid, and stained in Heidenhain’s iron-hematoxylin, nearly always 
contain one or more globules of varying sizes, probably of fatty 
‘material, since they are spherical, homogeneous, non-granular, 
and stain either a very deep blue or black (fig. 3, c, d). The 
cells are most irregular in shape and vary greatly in size, but 
they always lie in a clear area as if they had been fixed during 
the process of phagocytosis. — 
One can arrange a perfectly graded series of these included 
cells from the typical leucocyte to the wandering pigment cell. 
The first of the series is the small leucocyte consisting of almost 
nothing but a naked nucleus with its heavily staining nucleolus. 
This cell gives no evidence of phagocytizing the cells around it. 
Under favorable conditions a thin ring of cytoplasm can be seen 
surrounding the nucleus. The next step is a cell like the first 
except that the cytoplasm is more evident and there is most 
certainly the beginning of a clear area about the cell, showing 
that phagocytosis has begun. The third stage is the addition of 
