Studies on Regulation. 485 



why are certain structures formed in the new tissue of smaller 

 size or of less complexity in the absence of the ganglia ? It is 

 hoped that the following discussion of these points may throw 

 some light upon the problem and afford some hints for future 

 investigation. 



The only satisfactory answer to the above questions is to be 

 found in the differences in functional activity of the parts in the 

 two pieces. In the pieces with cephalic ganglia, the locomotion 

 being much more rapid and all movements more intense, the pos- 

 terior parts including the new tissue are used to a much greater 

 extent than in the pieces without ganglia. This greater functional 

 activity comprises many elements, attachment of the margins 

 and posterior end to the substratum and consequent tension 

 upon the parts; the constantly changing but characteristic me- 

 chanical conditions to which the parts are subjected in consequence 

 of the coordinated muscular activity and the pressure of the 

 intestinal contents and perhaps of other internal fluids resulting 

 from the movements; and the motor stimuli which may possibly 

 influence growth — these are some of the conditions which accom- 

 pany the motor activity of a given part, many of which in my 

 opinion may be formative factors. All of these conditions are 

 present in much greater degree in the pieces with intact ganglia, 

 and since the posterior part of the body has been removed, the 

 region of the cut surface and the new tissue as it appears must 

 be especially affected by them for these parts so far as function 

 is concerned supply the place of the parts removed. For example 

 in a case where the greater part of the body has been removed as 

 in Series 73 and 82, the region of the cut surface and the new tissue 

 arising from it are used by the animal, or at least the attempt is 

 made to use them, as the part removed would be used if it were 

 present. The greater the degree of functional activity affecting 

 these parts the greater the stimuli to growth and the more power- 

 ful the mechanical factors which assist in arranging the new 

 material or perhaps themselves stimulate growth. Thus the first 

 of the above questions finds its answer in the fact that the func- 

 tional activity of the regenerating region is greater in the pieces 

 with ganglia than in those without. I think no one who com- 



