Studies on Regulation. 549 



Pieces from the region anterior to the gangHa, those from the 

 extreme lateral margins of the body and those from the extreme 

 posterior end are almost incapable of regeneration and live but a 

 short time. 



In cases like that of Leptoplana where regeneration takes place 

 by the differentiation in a particular manner of new tissue formed 

 upon a cut surface it is very evident that the fate of the new tissue 

 is determined primarily by its relation to the old. The old part 

 is already definitely organized and functions in a particular man- 

 ner, thus determining the conditions to which the new tissue is 

 subjected. Attention has been called repeatedly to this relation 

 in the description and discussion of the experiments, and a close 

 parallelism between the amount and kind of motor activity and 

 the amount and rapidity of regeneration and the morphological 

 character of the regenerated part has been shown to exist. This 

 relation between motor activity and regeneration is undoubtedly 

 complex in character and requires some consideration. 



In the preceding paper (Child, '04b) the question of the relation 

 between the nervous system and morphogenesis was briefly dis- 

 cussed and attention was called to the possibility that an apparent 

 relation may exist in cases where the nervous stimuli themselves 

 are not the formative factors but merely determine the functional 

 conditions. Now that the description of the experiments is com- 

 pleted it is desirable to return to thi§ question and consider it in 

 the light of the experimental data. Three possibilities must be 

 considered: First among these is the question as to whether 

 nervous stimuli themselves exercise a "trophic" or a formative 

 influence. The experiments leave no room for doubt that some 

 considerable portion of the central nervous system must be present 

 in pieces from adult specimens of Leptoplana in order that life 

 may continue. Small anterior, lateral, and posterior pieces con- 

 taining only peripheral branches from the ganglia or cords die 

 within a few days. These facts may be regarded as indicating 

 that the nervous system is necessary for continued existence. But 

 since neither the ganglia nor the other parts which constitute a 

 head regenerate after removal of the ganglia we must conclude 

 either that the influence of the nervous system is not sufficient in 



