REGULATORY PROCESSES IN ORGANISMS 215 
v7. €., continued life. The new whole is, however, different from the 
old in size, physiological conditions, number and proportion of 
various parts, ete. 
In the process of regeneration in the stricter sense the new part 
is usually at first small and increases rapidly in size. I believe 
that this growth in size is assentially similar to the functional hy- 
pertrophy of organs. The part which was removed possesses a 
certain size in relation to other parts, because its size was deter- 
mined chiefly by correlative factors. Just so far as the new develop- 
ing part is subjected to similar correlative factors, it will 
tend to attain the same size as the part removed. Consequently 
it does not always attain the same size with respect to other parts. 
In Planaria the relative size of the new head differs according to the 
region of the body from which the piece is taken, to the nutritive 
condition aud various other factors. The process of reconstitu- 
_ tion ceases when a certain stage, differing under different condi- 
tions, is attained. This stage represents an equilibrium of physi- 
ological correlation, 7. e., of interaction between the parts; it is 
primarily a dynamic equilibrium, a proportioaality of processes, 
not of form. We can alter this condition of equilibrium experi- 
mentally by food, by starvation, by temperature, and in short by 
all factors which affect the processes. 
In various papers Driesch has distinguished a number of differ- 
ent forms of reconstitution (restitution). His distinctions are 
based primarily upon differences in the visible phenomena of 
development or dedifferentiation and for him the chief interest 
lies in the recognition of the different forms, rather than in the 
attempt to determine how they differ from each other physiologi- 
cally, since from his point of view the physiological factors are in 
many cases only ‘means’ which the entelechy employs. It is 
impossible to consider here these various forms of reconstitution, 
and since my point of view is so widely different from that of 
Driesch such a consideration would show merely that his basis 
of distinction could not be accepted for purposes of a physiological 
analysis. While it is convenient to distinguish different forms or 
methods of reconstitution, I believe that it is much more impor- 
tant to resolve the phenomena into processes. 
