Stiidn's on Regulation 369 



the very frequent slight contractions of the anterior and posterior 

 end all tend to keep the middle regions of the intestine more dis- 

 tended than the peripheral regions. 



Very probably the other functions, /. e., the digestive and storage 

 functions, also play a part in determining atrophy. Of course 

 absence of intestinal contents from any part of the intestme means 

 absence of food to be digested and stored up. Hence the cells of 

 this region may atrophy or change their character because of the 

 partial or total absence of the stimulus to the digestive function 

 or because of malnutrition: or again degeneration may occur 

 because the demands upon these cells for nutritive material are 

 so great in relation to the supply, that they are exhausted or forced 

 so far from equilibrium that continued existence is impossible: 

 degeneration from either of these causes would affect the peripheral 

 regions first and proceed toward the middle. 



But as will appear below, in certain experimental cases it is 

 impossible to account for the regulatory intestinal changes on 

 any other basis than that of mechanical stimuli from the contents. 



Ill INTESTINAL REGULATION IN CORRELATION WITH FORM- 

 REGULATION OF PIECES 



The character of form-regulation in general in this species was 

 described in an earlier paper (Child '05a). It will be recalled 

 that regulation after removal of posterior pieces consists almost 

 entirely in redifTerentiation of the parts remaining, only a very 

 small amount of new tissue being formed on the cut surface. 

 Posterior regulation is qualitatively, i.e., functionally, complete at 

 all levels except anterior to, in, and immediately posterior to the 

 cephalic ganglia. Regulation in the anterior direction, on the 

 other hand, consists almost wholly of regeneration, except as 

 regards certain cases of pharynx-formation, and is complete only 

 at levels anterior to, in, and immediately posterior to the ganglia, 

 being slight in amount elsewhere. 



As might be expected from these differences, intestinal regula- 

 tion is much more extensive in correlation with posterior than with 

 anterior regulation. But the most remarkable cases of intestinal 



