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In obedience to these, a division of the nucleus accompanies each qualitative change in the idioplasm, in which process the different qualities are distributed between the two resulting halves of the chromatin rods.'

Unfortunately, Weismann's hypothesis tells us nothing at all about these internal causes, that depend upon the physical nature of the idioplasm; that is to say, nothing at all about the causes which, working in a fashion so contradictory and astonishing, really produce the whole development.

The presence of idioplasm in all parts containing the primary constituents does not help us in this respect.'

Cells and cell-properties are essential parts of Weismann's theory; while Naegeli has attempted to make his theory of the idioplasm independent of the whole conception of cells.

In investigating Darwin's pangenesis, Galton's doctrine of the stirp, Naegeli's idioplasm, Weismann's germplasm, the intracellular pangenesis of De Vries, His' doctrinal of germinal foci for the formation of organs, or Roux's mosaic theory, I believe that one must face the question: How far do these doctrines agree with what we know about the structure and function of the cell?