380 C. M. Child 



In short, when we consider the various features of this pecuHar 

 regulation as primarily "functional adaptations" or better as func- 

 tional regulations, the morphological changes and results are 

 readily interpreted. Moreover, I fail to see any other possible 

 basis for interpretation. That additional factors may be involved, 

 which have not been recognized, is extremely probable, but the 

 facts themselves seem to me to indicate that mechanical conditions 

 play a large part in determining the character of the functional 

 regulation, which, in my opinion, is the basis of the morphological 

 changes. Undoubtedly the process is, at least in large part, a 

 complex physiological reaction, not a simple mechanical distortion. 



2 Intestinal Regulation in Correlation zuith Anterior Form- 

 er 



Regulation 



Anterior regulation is complete only at levels anterior to, 

 through, and immediately posterior to the cephalic ganglia. The 

 parts replaced are replaced chiefly by regeneration from the cut 

 surface. In the case of regeneration of the head the ingrowth of 

 the intestine into the new tissue requires no special consideration 

 here, since it is similar to intestinal regeneration in various other 

 species of turbellaria. 



In certain cases, however, in which the anterior end has been 

 removed posterior to the ganglia and no new head is formed, cer- 

 tain features of interest appear and these are considered briefly 

 below. 



Pieces from which the anterior end has been removed at a level 

 not far posterior to the cephalic ganglia {a, Fig. i) behave and 

 react more like normal animals than pieces from which more of 

 the anterior end has been removed: they are more active and react 

 to slighter stimuli than the other headless pieces, but do not regen- 

 erate heads, although they produce more new tissue anteriorly 

 than the others (Child '05a, '05c). In such pieces the only visible 

 changes in the intestine consist in reduction of a type resembling 

 that observed in normal animals. Fig. 13 shows a piece from 

 which the anterior end was removed at a level corresponding to a, 

 Fig. I. The specimen was originally somewhat smaller than that 



