One of the most important facts in connection with the organization is that a part, if separated from the rest, may become a new whole, and this appears to be a fundamental peculiarity of living things. Analogies can be found, perhaps, in inorganic phenomena, as for instance a storm dividing into two or more parts and each developing a new storm centre of its own, or when a suspended drop is divided and each half becomes a new sphere; but these comparisons lack some of the essential features of the organic phenomenon. A progressive change takes place as development proceeds, so that a stage once passed through is not repeated if a part is separated from the rest, as illustrated by Driesch’s experiments with the blastula and gastrula of the sea-urchin and starfish, and by the method of development of pieces of the adult, that do not pass through the embryonic stages. As the protoplasm changes new conditions may arise, either because the protoplasm in its new form can be acted upon by those internal or external conditions to which it did not respond at first, as Driesch has supposed, or, as I think equally probable, because the series of reactions that have begun with the first step in the development work themselves out in the same way that a chemical reaction once started may pass through a long series of stages depending upon the nature of the substance. The difference between these views lies in this, that the former supposes latent substances, or elementary processes or forces, whatever they may be called, to be present in the egg and to act when a medium that responds to them has come into existence; the other idea supposes that the whole process is started with the first change and once set going is of such a kind as to continue to an end through a regular series of stages. Both views are suppositions, and, it may be, reduce themselves ultimately to the same thing.