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- 
