Nägeli has stated that each part acts as though it _knew_ what the other parts are doing. His idea of the idioplasm involves a conception of the organism as a whole and not simply the sum total of a number of parts. Hertwig, who maintained at one time that the development of the embryo is the resultant of the action of the cells on each other, admits in his work on _Die Zelle und die Gewebe_ that while this is in part true, yet on the other hand the whole also exerts an influence on its parts. Driesch, who hypothetically suggested at one time that the nuclei act as centres of control of the cell by means of enzymes, has later adopted a widely different view. Whitman has made a strong argument to the effect that the cell theory is too narrow a standpoint from which to treat the organism, and on several occasions I have urged that the organism is not the sum total of the action and interaction of its cells, but has a structure of its own independent of that of the cells. This discussion will suffice to show some of the opinions that have been held as to the nature of the organization of the organism. Let us next ask what properties we may ascribe to it. It has been found that certain polar, or rather dimensional, relations are characteristic of the organization. The term “polarity” expresses this in a limited way, but refers only to one line having two directions, while we now know that the dimensional properties relate to the three dimensions of space, and for this idea we might make use of the term heterotropy. Thus we find that a piece of a bilateral animal regenerates a new anterior end from the part that lay nearer the anterior end of the original animal, a new right side from the part that was nearest the original right side, and a new dorsal part from the region that lay near the original dorsal part, etc. The polarity of a part can be changed in certain forms, as in tubularia, by exposing the posterior cut-end to the external factors that bring about the formation of a hydranth, or, as in hydra, by grafting in a reversed direction a smaller piece on a larger one. In _Planaria lugubris_ and in the earthworm the polarity of the new tissue may be reversed, as compared with that of the part from which it develops, if the new part arises from certain regions of the body. A curious instance of the effect of the polarity is shown by the regeneration from an oblique surface in planarians. The new head arises from the more anterior part of the new material, rather than from the middle of the anterior oblique surface, and the new tail arises from the more posterior part of the posterior oblique surface. As an analysis of this result has been already attempted in an earlier chapter, it will not be necessary to go further into this question here.