Much misunderstanding has arisen in connection with the term “formative force.” In the first place we naturally associate with this term the meanings attached to it by writers of the seventeenth and eighteenth centuries. They assumed a formative principle in living things, that is an expression of a formative force. Roux, who has more recently used the term, has attempted to avoid misunderstanding by using the plural,--“the formative forces of the organism”; but even under these circumstances, differences of opinion have arisen, as shown by the controversy between Roux (’97) and Hertwig (’94 and ’97), on this point. A change in form carries with it a change of position of the parts, and the latter involves the idea of forces, but the nature of these forces is entirely obscure to us, at least we cannot refer them to any better-known category of physical or chemical forces. They may, perhaps, be most profitably compared to the forces of chemical union, but whether they are very numerous or can be reduced to a limited number of kinds of force, we do not know. If it could be shown that the changes in the organism are due to molecular changes, then the formative forces might appear to be only molecular forces, but we are not in position at present to demonstrate that this is the case, however probable it may appear. Finally, the use of the term “organization” may be considered, although from what has been said already it is clear that there must be a certain amount of vagueness connected with our idea of what the organization can be. The organization, from the point of view that I have adopted, is a structure, or arrangement of the material basis of the organism, and to it are to be referred all the fundamental changes in form, and perhaps of function as well. We also use the term as applied to the completed structure, by which we mean that the organism consists of typical parts having a characteristic arrangement carrying out definite functions. When applied to the egg, or to a regenerating piece, the term refers to some more subtle structure that we are led to suppose to be present from the mode of behavior of the substance. As pointed out, we know this organization at present from only a few attributes that we ascribe to it, and are not in a position even to picture to ourselves the arrangement that we suppose to exist. _REGENERATION AND ADAPTATION_