210 Cc. M. CHILD 
conditions existed at the beginning or elsewhere in the course of 
the regulation, and in many cases we can determine what those 
conditions are. For example, pieces of Planaria which give rise to 
‘wholes’ at a certain temperature and under certain other conditions, 
can be made to produce headless forms or tailless heads, accord- 
ing to the region of the body from which they are taken, by sub- 
jecting them to lower temperatures, by starving the animals before 
beginning the experiment, by placing the pieces in dilute alcohol 
or ether, etc. Nothing has gone astray in these cases, there is no 
error, the same laws have been followed as when ‘wholes’ are pro- 
duced, different conditions simply lead to different results. Else- 
where (Child, ’10c) I have attempted to analyze some of the con- 
ditions which bring about so-called heteromorphosis in Tubu- 
laria and other forms, and have shown that they are similar in 
character to those which bring about asexual reproduction in 
nature. 
There are many cases in which the occurrence of reconstitution 
as opposed to restitution is so obvious that there can be no ques- 
tioning it. A piece from the body of Hydra, for example, does not 
restore the missing parts, but reconstitutes itself into an organism, 
smaller, simpler, possessing fewer tentacles and undoubtedly 
physiologically younger than the original animal. In Clavellina 
also, as Driesch himself has shown (Driesch, ’02), the isolated 
branchial region or a part of it does not replace the missing parts, 
but undergoes a process of reconstitution. In these cases the physi- 
ological effect upon the parts remaining of the removal of cer- 
tain parts is so great that these parts do not retain their original 
structure, and a dedifferentiation and redifferentiation occurs. 
But the effects so apparent in these cases are simply more extreme 
than in cases where only a small part isremoved. Przibram (’07) | 
has called attention to a number of cases which show very clearly 
that the removal of a part results, not in the restoration of the 
original, but in the establishment of a new equilibrium, differing 
more or less widely from that. 
It is obvious that the process of reconstitution is an equilibra- 
tion and just as obvious that it leads to different results under dif- 
ferent internal and external conditions. As different rivers differ 
