538 C. M. Child. 



representing in themselves a "head" or other morphological 

 features are present it is difficult to believe. The head of Lepto- 

 plana, like other parts of the body, represents the effect of a series 

 of characteristic activities upon a given complex of substances in 

 a given environment. 



B. LATERAL REGENERATION. 



Only a brief consideration of the phenomena of lateral regener- 

 ation is necessary since the relations are not essentially different 

 from those already described for anterior and posterior regenera- 

 tion. In general the amount and rapidity of lateral regeneration 

 in the presence of the cephalic ganglia are directly proportional 

 to the amount of tissue removed. In the absence of the ganglia 

 the amount and rapidity of regeneration differ in different cases; 

 if the size of the part removed is not great the amount and rapidity 

 of regeneration are directly proportional to it; if on the other hand 

 the portions removed constitute the greater part of the body the 

 amount and rapidity of regeneration are inversely proportional 

 to the size of the part removed Qualitatively, however, lateral 

 regeneration resembles in most respects posterior regeneration, 

 in that absence of the cephalic ganglia does not alter the structural 

 character of the regenerated tissue except in the extreme anterior 

 region, though it does reduce its amount. 



As in the case of anterior and posterior regeneration it was found 

 that when about half or more of the ganglionic tissue was present 

 complete regeneration occurred, but when less than this amount 

 was present the results approached those obtained from pieces 

 without ganglia. Specimens separated into halves along the 

 median line, each half containing one-half of the ganglionic mass, 

 were capable of complete regeneration (Child, '04a). If, how- 

 ever, the plane of section did not coincide with the median plane 

 complete regeneration occurred only in the piece containing the 

 larger part of the ganglionic mass. 



As might be expected the relation between the cephalic ganglia 

 and motor activity is the same in pieces cut longitudinally as in 

 other pieces. When half or more of the ganglionic substance is 

 present the pieces behave essentially like normal animals, but 



