CELLS LINING THE PERITONEAL CAVITY 405 
2. Cells covering the omentum. 
3. Cells covering the spleen. 
A. Cells covering the ovary, the so-called germinal epithelium. 
The first division is a composite one, including all the cells 
which have no very sharp differences from each other, and 
besides all of these cells agree in general in storing smaller amounts 
of the dyes than do those of the spleen and ovary and differ 
from the cells of the omentum in certain peculiarities other than 
the amount of dye stored. The lining cells of the mesentery 
are very much like those of the omentum, but have cer- 
tain local differences which are more like the general lining cells 
elsewhere, thus placing the cells covering the mesentery midway 
between the ordinary serosal lining cells and the cells covering 
the omentum. In this way there are all gradations between 
the cells covering the intestine which take less vital dye than 
any other serosal cells, and the cells covering the spleen and the 
ovary, both of which show a characteristic vital staining with 
considerable ease. The other variations and what evidence 
there is of a parallel physiological relationship will be taken up 
later. 
The most obvious characteristic which has been observed in 
the manner in which the lining cells store vital dyes is the collec- 
tion of the dye concretions into an area more or less regular in 
shape in a definite portion of the cytoplasm. The distribution 
of dye-granules in a perinuclear rosette is also characteristic of 
the serosal cells, but requires longer exposure to the dye for its 
development and is never so universally present as the specific 
separate mass in the cytoplasm. These two specific types of 
staining are often found combined, but each and particularly 
the clump of granules may appear alone or with many minor 
variations, which are in part characteristic of the cellular surface, 
in part the result of the kind of dye employed, but to a greater 
extent due to the length of time during which the cells have been 
exposed to the dyes. Again it has been noted in general that 
carmine tends to remain more definitely collected in a small area, 
while trypan blue tends much more to form perinuclear rosettes, 
usually with, but sometimes without, local concentrations. It 
