46 Nature of the Formative Stimulus 



ing somewhat for example with the alternating electric 

 current, or indeed might arise in another way of which 

 perhaps we can not in advance form any conception at all. 

 It is sufficient for our purpose, we repeat, to suppose that 

 these specific modes of being can combine and break up 

 according to laws which are definite even though so far 

 quite unknown. For the very fact of the existence of 

 these laws would imply also the existence of correspond- 

 ing laws on which the circulation or distribution of 

 nervous energy in definite networks would depend. 



If one accepts such a hypothesis of the circulation 

 or the distribution of nervous energy in the organism, 

 one could find the immediate explanation of certain 

 phenomena of development whose cause has so far 

 remained a secret. These phenomena consist in the recip- 

 rocal influences which certain parts of the embryo, even 

 though widely separated, exert upon one another in spite 

 of the lack of any functional adaptation and by which the 

 development of these parts is wholly or partially 

 determined. 



One can, indeed, attempt to give the beginning of 

 an explanation of these phenomena of correlation, by 

 supposing the different parts which exercise this reciprocal 

 influence to be situated, maybe upon the same partial 

 network of the general circulatory system, maybe upon 

 different partial networks which nevertheless come off 

 at one common given point from the same principal 

 branch, or maybe finally, in the case of contiguous parts, 

 upon different partial networks which are however 

 provided with direct communications between some of 

 their respective nuclei. The absence of any analogous 

 reciprocal action between other parts also contiguous 

 may be explained by the lack of any such direct con- 



