208 Cc. M. CHILD 
brings about not simply its restitution, but an equilibration 
extending more or less widely, and strictly speaking, probably 
throughout the system. The system reconstitutes itself and the 
whole formed is different from the original quantitatively or 
qualitatively. The whole process is a complex of equilibrations, 
of compensations and transformations, resulting in that which 
we call a whole, but no two wholes are alike. 
If for example, we consider this process in a piece of the Plan- 
arian body, we find that it differs in rate and character according 
to size of the piece, region of the body from which it is taken, tem- 
perature and other factors which influence metabolism. The ani- 
mal formed as the result resembles the original in its general shape 
and activity, but it is far from being identical with it. It is usually 
smaller than the original, the pharynx may be in quite different 
position in the body, and the arrangement, number and form of the 
intestinal branches differs more or less widely, according to con- 
ditions. Moreover, under various conditions, various degrees 
and kinds of incompleteness appear. Some pieces develop only a 
single eye, or the eyes are partially fused or otherwise different 
from those in the original animal,some pieces develop no pharynx 
and no posterior end, others no head or-an ‘imperfect’ one, some 
develop the postpharyngeal intestinal branches more rapidly 
and more completely, others the prepharyngeal branches, some 
produce a larger, others a smaller head, some show niore ‘regen- 
eration,’ others more ‘redifferentiation’ and so on. If we place 
the different sorts of wholes under closely similar conditions and 
give them food they become more or less like each other because 
these conditions bring about further regulations but these regu- _ 
lations do not properly belong to the regulatory process which re- 
sulted from the isolation of the part, but are independent of it and 
are such as were occurring in the original animal during its life. It 
is probably not too much to say that no two pieces of the 
Planarian body attain the same condition in the process of regu- 
lation. When we say that because some or all of them produce 
wholes they are all potentially alike, we are simply assuming that 
all wholes must be alike, which is obviously untrue. As each piece 
is different at the start from the others, so it attains a different 
