EXPERIMENTAL MORPHOGENESIS 117 



satisfactory ; for what has to be done in restitution in 

 each case is not a simple homogeneous act, for which one 

 special material might account, but is a very complicated 

 work in itself. It was the defect of the theory of " organ- 

 forming substances " as advocated by Sachs, that it over- 

 looked this point. 



So all we know about the proper stimuli of restitutions 

 is far from resting on any valid grounds at all ; let us not 

 forget that we are here on the uncertain ground of what 

 may be called the newest and most up-to-date branch of 

 the physiology of form. Xo doubt, there will be something 

 discovered some day, and the idea of the " whole ' in 

 organisation will probably play some part in it. But in 

 what manner that will happen we are quite unable to 

 predict. 



This is the first time that, hypothetically at least, the 

 idea of the whole has entered into our discussion. The 

 same idea may be said to have entered it already in a 

 more implicit form in the statement of the threefold 

 harmony in ontogeny. 



Let us now see whether we can find the same problem 

 of the " whole' 1 elsewhere, and perhaps in more explicit 

 and less hypothetical form. Let us see whether our 

 analytical theory of development is in fact as complete as 

 it seemed to be, whether there are no gaps left in it which 

 will have to be filled up. 



