No. 2.] COMPARATIVE CYTOLOGICAL 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., those of egg cells in the maturation period, those of the 

 subcuticular gland cells of Piscicola, the mesenchym cells of 

 Cerebratiihis. 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. 



