No. 2.] COMPARATIVE CYTOLOG/CAL STUDIES. 
535 
consisting of a substance, or different substances, taken into 
the nucleus from the cell body. It seems probable, further, 
that these substances stand in some relation to the nutritive 
processes of the nucleus, and in a relation to the growth of the 
latter. Thus those nuclei which are characterized by an espe¬ 
cially large amount of nucleolar substance are growing nuclei, 
i.e.y those of egg cells in the maturation period, those of the 
subcuticular gland cells of Piscicola , the mesenchym cells of 
Cerebratulus . In the gland cells of Piscicola the volume of the 
nucleolar substance rapidly increases in amount during the 
phase of growth of the nucleus, but diminishes when the latter 
decreases in volume. Somatic cells, on the contrary, at least 
those which are undergoing no dimensional changes, contain 
a relatively small amount of this substance. It* is doubtful 
whether Hacker (’ 95 ) is quite correct in assuming that the 
amount of the nucleolar substance stands in a direct proportion 
to the intensity of the functional changes which take place 
between the nucleus and the cytoplasm; at least there are but 
few criteria to enable one to compute the degree of such an 
intensity. Thus one would suppose that in nerve cells there 
was a close and intimate correlation between nucleus and cell 
body, but the nucleoli of the ganglion cells of the nemerteans 
and Piscicola are very small. Hacker’s deduction might be 
modified as follows : where there is a close physiological rap¬ 
port ', in regard to processes of nutrition, between the nucleus 
and the cell body a relatively large amount of nucleolar sub¬ 
stance occurs in the former. 
Accordingly, we find a relatively large amount of nucleolar 
substance in growing nuclei, and hence conclude that this sub¬ 
stance stands in some connection with the processes of nutrition, 
is itself either nutritive in function or represents that portion of 
substances assimilated by the nucleus from which all nourish¬ 
ment has been extracted, and in this case it would be a waste 
product. A third possibility is that the nucleoli may represent 
accumulations of nutritive substance retained in the nucleus as 
a reserve supply; but this does not seem to be very probable, 
for by this assumption it would be difficult to explain the uni¬ 
formity in the size of the nucleoli in a given species of cell. 
