Studies on Regulation. • 493 



Or we may put the case in a somewhat different form : admitting 

 that the total amount of regeneration is proportional to the degree 

 in which the conditions for regeneration are present, each part of 

 the regenerating portion attains a certain size and form which 

 represent in a way the proportionality between the stimuli affect- 

 ing it and those affecting other parts. If, as I have suggested, 

 these stimuli are at least in part the functional stimuli, we may say 

 that the size of the pharynx in a regenerating part is dependent 

 upon the size of the part and upon the relation between functional 

 conditions affecting the pharynx and those affecting other regions. 



In short, the difference in size of the pharynx in the pieces with 

 and those without ganglia is simply a particular expression of the 

 factors which determine the difference in the amount of regenera- 

 tion in the two cases, viz: the functional conditions. If, as 

 Bardeen ('01, '03) supposes, the pressure of the intestinal contents 

 is a factor in the formation of the pharynx, it is evident that this 

 factor must be present in much greater degree in the pieces with 

 ganglia since the movements and muscular contractions of the 

 various parts which force the intestinal contents out of the 

 branches toward the central parts are much more frequent and 

 intense in these pieces than in the others. At any rate it is evident 

 that the regenerating part is functionally active in much greater 

 degree in the presence of the ganglia, and since I believe that the 

 various conditions connected with functional activity are impor- 

 tant factors in the production and maintenance of organic form, 

 the difference in size of the regenerated pharynx in the two sets is 

 in full agreement with the other facts already discussed. 



The extent to which the intestinal branches regenerate also 

 differs in the pieces under consideration. Examination of the 

 figures will show that in every case, even in the earlier stages, the 

 regeneration of the intestinal branches is more advanced in the 

 pieces with ganglia. Compare Figs. 8 and 1 1 (ganglia present) 

 with Figs. 7, 9 and 10 (ganglia absent). Figs. 13, 15 and 16 

 (ganglia present) with Figs. 14, 17 and 18 (ganglia absent), and 

 Figs. 20, 21, 24, 25 (ganglia present) with Figs. 22, 23, 26, 27 

 (ganglia absent). 



The intestinal branches appear to rise in all cases from the cut 



