26 EDWIN G. CONKLIN 
which are frequently filled with vacuoles and sap so that the size 
of the cell gives no true idea of the volume of the cytoplasm. 
Among animals adult tissue cells often become filled with the 
products of differentiation or metabolism, such as fibers, granules, 
secretions, oil, etc., which greatly increase the cell dimensions. 
It is evidently a difficult if not impossible task to determine the 
quantity of real protoplasm in such cells and thus to discover the 
true “Kernplasma-Relation.’’ However in certain less highly 
differentiated cells, especially in epithelial and glandular tissue, 
the true Kernplasma-Relation may be established with a fair 
degree of accuracy. 
Unquestionably the physiological state of a cell has much to 
do with its nuclear-plasmic ratio. Hodge (’92) found the nuclei 
of nerve cells shrunken after extreme stimulation, and it has been 
long known that the same is true of gland cells. In Crepidula 
the liver cells, when active, are filled with secretion and are among 
the largest in the body, but when the secretion has been discharged 
and they have returned to an inactive condition, the cell body is 
much smaller and the nucleus larger. 
I have measured the cells and nuclei of a number of tissues of 
Crepidula plana, derived from the three germ layers, and the 
results are given in table 7. Since these cells vary in shape to a 
great extent, and in order to facilitate comparison of cell diam- 
eter and nuclear diameter, cells were chosen for measurement 
which were as nearly as possible spherical or cubical in shape. 
‘In all elongated cells the long axisand one cross axis were measured 
and it was assumed that the other cross axis was of the same di- 
mensions as the one observed. 
It is evident that in these tissue cells of Crepidula plana there 
is no marked increase of protoplasm over nucleus as compared 
with the blastomeres of the same species; throughout the cleavage, 
with the exception of the cells 3A-3D and 4A-4D, the average 
Kernplasma-Relation for nuclei and cells of mean size is about 
1 : 15, for nuclei and cells of maximum size about 1 : 6; the aver- 
age ratio in adult tissue cells, which are not filled with metabolic 
products, is about 1:10.5. In the case of the ganglion cells the 
nuclei are relatively and absolutely larger than in the other tissues, 
