Studies on Regulation. 521 



(Fig. 5). I am inclined to believe that functional conditions may 

 account in large part for this difference. The larger the part 

 which the new tissue represents the greater and more varied is its 

 activity and if the various conditions connected with this activity 

 affect growth in any way a more or less exact proportionality 

 between the rapidity of regeneration and the size of the part 

 removed may be expected. 



3. Anterior Regeneration from Levels Immediately Posterior to 

 the Cephalic Ganglia. 



Anterior regeneration from levels only a short distance poste- 

 rior to the cephalic ganglia differs in certain respects from that 

 occurring from levels farther removed from the ganglia. Al- 

 though nothing like a head is ever regenerated the amount of 

 regeneration is usually somewhat greater than at other levels 

 posterior to the ganglia and the new tissue possesses a somewhat 

 different form. Individual differences which occur are doubtless 

 due in part to slight differences in level of the plane of section, 

 though, as will appear below, some cases indicate that internal 

 factors differ in different individuals. The history of a series 

 will serve to illustrate these points. 



Series Ji. The head and ganglia were removed from a number 

 of large specimens by a cut just posterior to the ganglia as in 

 Fig. 14. In all cases this cut was made as near as possible to the 

 eyes, but without including any part of them in the posterior 

 piece. All pieces were examined after section and those in which 

 eyes were present in the posterior piece or in which the plane of 

 section lay too far posteriorly were discarded. Five posterior 

 pieces were finally obtained for the experiment. 



A few hours after section all pieces appeared much like Fig. 15; 

 contraction of the cut surface had occurred and as is usual in 

 pieces without ganglia considerable longitudinal contraction had 

 occurred so that the width of the body was greater than before 

 section. 



The pieces were examined every few days and the following 

 figures show the condition of the various pieces six, seventeen and 

 thirty-two days after section. Three types were recognizable as 



