Studies on Regulation. ■ 525 



these pieces differences of this kind cannot be correlated with 

 differences in the size of the part removed, since this was approxi- 

 mately the same in all cases. They are rather to be compared 

 with the cases described in the preceding paper (Child '04b) in 

 which the rapidity and amount of posterior regeneration from a, 

 given level was much greater in the presence of the ganglia than in 

 their absence, and I believe that they are to be explained in the 

 same manner, viz: as due chiefly to differences in motor activity. 

 Numerous similar experiments afforded similar results. In no 

 case did a characteristic head regenerate in the absence of the 

 ganglia, but regeneration from a level immediately posterior to 

 the ganglia was in almost every case more rapid and greater in 

 amount than from more posterior levels. Moreover, whenever 

 differences in motor activity could be distinguished the most 

 active pieces showed the greatest amount of regeneration. 



4. Anterior Regeneration from Other Levels Posterior to the 

 Cephalic Ganglia. 



When both the ganglia and the region immediately posterior to 

 them are removed, anterior regeneration is usually even less in 

 amount than in the cases above described; occasional exceptions 

 to this rule occur, however, some of which will be described below. 

 But in general the amount of anterior regeneration from these 

 levels is inversely proportional to the size of the part removed, or 

 in other words, the farther posterior the level from which it occurs, 

 the less the regeneration. This relation is exactly the reverse of 

 that observed in connection with posterior regeneration (Child, 

 '04b); there the amount of regeneration is directly proportional 

 to the size of the part removed. 



My experiments along these lines include nearly two hundred 

 specimens but with only one marked exception as regards the 

 amount of new tissue and three cases in which a few eye-spots 

 appeared. Experiments in three different regions are selected 

 for description. The levels are indicated by the three unbroken 

 transverse lines in Fig. 27. The results obtained from section at 

 the most anterior of these three levels are indicated in Figs. 28-35. 

 Figs. 28-31 represent the history of a piece in which the cut surface 



