28 EDWIN G. CONKLIN 
Crepidula the embryonic ratio of nucleus to plasma is main- 
tained with little change. In all the odcytes up to the time that 
yolk formation begins the nuclei are relatively large, the ratio 
of nucleus to plasma being about 1 : 3.6, and in the younger and 
smaller odcytes the nuclei are relatively larger than in the older 
and larger ones. 
Eycleshymer (’04) found that the volume of the plasma in the 
striated muscle cells of Necturus increased about ten times as 
much as the nuclear volume, during development from the 8 mm. 
embryo to the adult condition. There is, therefore, in these later 
stages a notable shifting of the Kernplasma-Relation in favor of 
the plasma. It is probable however that the contractile substance 
which makes up the larger part of the muscle cell, does not con- 
tribute to the growth of the nucleus as does the protoplasm of 
embryonic cells—that so far as the growth of the nucleus is con- 
cerned it acts as does yolk, oil, membranes, fibers and other 
products of metabolism and differentiation. If only the sarco- 
plasm of the muscle cell and not its contractile substance is able 
to contribute to the growth of the nucleus, the small volume of the 
nuclei as compared with the entire cell would find a ready explan- 
ation. There can be no doubt that the plasma is the chief seat 
of differentiation, as Minot has emphasized, and that highly 
differentiated cells, such as muscle, nerve, and some kinds of 
connective tissue, have a larger amount of plasma and its products, 
relative to the nucleus, than have embryonic cells. In the case 
of fiber cells, fat cells, and probably muscle cells, the cell body 
becomes filled with the products of differentiation and metabo- 
lism, which like the yolk in egg cells, or the secretion products in 
liver cells cannot enter the nucleus and consequently do not influ- 
ence its size. In such tissue cells the cell body is relatively much 
greater as compared with the nucleus, than in purely protoplas- 
mic cells, but I have been unable to find any evidence that the 
ratio of protoplasm (using this term in its usual sense) to the 
nucleus is greater in tissue cells of Crepidula than in the blas- 
tomeres. 
