REGULATORY PROCESSES IN ORGANISMS 209 
result. Driesch’s assumption of ‘equipotentiality’ of different 
parts is shown by the facts themselves to be incorrect, and I 
believe that his ‘harmonious-equipotential systems’ do not exist 
in nature, as systems capable of development but only as ab- 
stractions of the human mind. 
For these reasons the term ‘restitution’ seems tome to carry with 
it implications which, when we analyze them, we cannot, in the 
light of the facts, accept. The piece does most certainly not 
restore what it lost: it reconstitutes itself into something more or 
less widely different from that of which it formed a part, and this 
something often possesses visible structural characteristics which 
we have come to regard as characteristic of a whole. Seeing these 
resemblances, we abstract from the differences and say that it is 
the same as that of which it formed a part. 
Closer examination shows us that even visibly it is not the same, 
but different; moreover, visible characteristics are not the sole 
criterion of resemblance and differencein organisms. The processes 
occurring are just as characteristic as the visible structure. I 
have shown elsewhere (Child, ’11b) that in Planaria the process 
of form regulation results in a rejuvenation, the pieces after 
undergoing regulation are physiologically younger than the ani- 
mals from which they were taken, and the degree of rejuvenation 
varies with the degree of reconstitutional change. Manifestly 
then these pieces are not the same after regulation as the wholes 
of which they formed parts. To say that they are is simply to 
deny the facts as they stand before us. 
In many cases, moreover, the pieces do not produce anything 
that can be called a whole. Pieces of Planaria may produce 
double heads or double tails, tailless heads orheadless forms. For 
those who with Driesch regard the formation of a ‘whole’ as the 
uniform result of so-called restitution, these cases are difficult to 
interpret. The process of regulation has apparently followed the 
wrong track, it has gone astray and so failed of the correct result. 
But when we take the position that the part, when isolated, under- 
goes a reconstitution, which differs in its results according to the 
existing conditions, internal and external, we see that these ‘abnor- 
malities’ differ from ‘normal’ results simply because different 
