SOME PROBLEMS OF CELL-ORGANIZATION The remarkable history of the chromatic substance in the maturation of the germ-cells forces upon our attention the problem of the ultimate morphological organization of the nucleus, and this in its turn involves our whole conception of protoplasm and the cell. The grosser and more obvious organization is revealed to us by the microscope as a differentiation of its substance into nucleus, cytoplasm, and centrosome. But, as Strasburger has well said, it would indeed be a strange accident if the highest powers of our present microscopes had laid bare the ultimate organization of the cell. Brucke insisted more than thirty years ago that protoplasm must possess a far more complicated morphological organization than is revealed to us in the visible structure of the cell, and suggested the possible existence of vital units ranking between the molecule and the cell. Many biological thinkers since Brucke's time have in one form or other accepted this conception, which indeed lies at the root of nearly all recent attempts to analyze exhaustively the phenomena of cell-life. I shall make no attempt to review the a priori arguments that have been urged in favour of this but will rather inquire what are the extreme conclusions justified by the known facts of cellstructure.