Studies on Regulation. 507 



thus confirming the suggestion already made regarding the 

 earlier stage of regeneration (pp. 487 and 488). 



In all cases pieces from the region anterior to the cephalic 

 ganglia died within two or three days after section. In some of 

 these a small amount of unpigmented "new" tissue appeared upon 

 the cut surface but the early death of the pieces prevented further 

 regeneration. 



e. Resume of Experiments on Posterior Regeneration. 



The experiments described show that the presence of the ceph- 

 alic ganglia is not necessary for regeneration in the posterior 

 direction at any level posterior to the ganglia. When they are 

 present the size of the regenerated part is larger but regeneration 

 is qualitatively complete in their absence. From these facts we 

 are justified in concluding that no "formative stimuli" for the 

 parts under consideration proceed from the cephalic ganglia. 

 The relation between the ganglia and the amount of regeneration, 

 on the other hand, shows that the conditions upon which regenera- 

 tion depends are quantitatively affected by the presence of the 

 ganglia. As I have endeavored to show, the facts indicate that 

 at least certain of these conditions are those resulting from the 

 characteristic motor activity of the animal; probably other func- 

 tional conditions besides those connected with movement are also 

 concerned, though their existence is less readily demonstrated. 



The difference in motor activity of the posterior parts between 

 the pieces with and those without cephalic ganglia is essentially 

 one of degree; in the absence of the ganglia all conditions and 

 stimuli connected with motor activity are less intense and occur 

 in less orderly sequence, though very probably none are wholly 

 absent. If these are "formative factors" it follows that the re- 

 generative processes must occur in less degree in the absence of 

 the ganglia. According to this view the relation between the 

 ganglia and regeneration is indirect, not direct; the ganglia are not 

 the "centers" for special formative stimuli, but are merely more 

 or less complex portions of the nervous system connected on the 

 one hand with certain sense organs and on the other with other 

 parts of the nervous system and so with the various regions of the 



