288 RE GENERA TION 



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 misunderstand- 

 ing 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 com- 

 pared 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 organ- 

 ism 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 arrange- 

 ment carrying out definite functions. When applied to the egg, 

 or to a regenerating piece, the term refers to some more subtle struc- 

 ture that we are led to suppose to be present from the mode of be- 

 havior 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 



One of the most difficult questions with which the biologist has 

 to deal is the meaning of the adaptation of organisms to their environ- 

 ment. Pfluger, in an article entitled "The Teleological Mechanics of 

 Living Nature," has drawn attention to the teleological character, or 

 purposefulness, of certain processes in the living organism. " There 



