l66 C. M. CHILD. 



clearly dissociate the idea of organic structure from the dynamic 

 activities which it exhibits. For the sake of critical analysis, 

 however, it is necessary to emphasize the fact that organic struc- 

 ture is primarily a typical arrangement of heterogeneous com- 

 ponents without regard to their constitution. This becomes 

 evident at once from the following consideration : if each com- 

 ponent of a given organic structural complex could be distin- 

 guished it would be possible to build up artificially an identical 

 structure in which each component was different in constitution 

 from the corresponding component in the original structure. On 

 the other hand, if all the different components of an organic 

 structural complex could be isolated without altering their con- 

 dition and then mixed together the mixture would not represent 

 the original structure. 



It thus becomes evident that the space-relations of the com- 

 ponents, not their constitution, are the characteristic feature of 

 structure proper. From this conclusion it follows that formative 

 substances, if they exist, must be specific substances which de- 

 termine the arrangement of the component parts of a structural 

 complex. In order to determine whether formative substances 

 do exist we have first to consider the possible methods of origin 

 and action of such substances. As regards the individual, for 

 example, each substance must either be represented in the prim- 

 itive germ-cell by an ultimate " unit of organization " of the 

 same nature as itself, or it must have arisen from other sub- 

 stances in the course of development. 



In the one case development is merely the " unfolding," "ac- 

 tivation," or whatever we prefer to call it, of preformed " germs," 

 "determinants," or "definite, determinate and primary " units 

 of organization. In the other case it is, properly speaking, an 

 epigenesis, in the course of which new formative substances ap- 

 p -ar as the result of the activity of others, and the complexity 

 of the developing organs increases. 



Directing our attention first to the preformation hypothesis we 

 must inquire as to the nature of these ultimate units which 

 represent both the formative substances and the structures of 

 laler stages. Are they simply molecules or groups of similar 

 molecules, or are they something more complex? 



