StiiJ/t's oil Rt'gulntion jgj 



ments ot the hypothesis and 1 tail to see how any other interpre- 

 tation of them is possible. They all indicate that the rapidity of 

 degeneration of the intestinal branches is dependent, at least in 

 large measure, on the degree of change in the mechanical func- 

 tional conditions connected with the presence and movements of 

 the intestinal contents, irrespective of their nutritive value. 



But when we compare normal animals with pieces which pos- 

 sess heads the case is somewhat different. The very rapid intes- 

 tinal degeneration in the redifferentiating regions of such pieces 

 has already been discussed in Section III c, and does not concern, 

 us here, but the rapidity of intestinal degeneration in othpr parts 

 of the body differs from that in normal animals and also differs 

 according to the length of the pieces. In such pieces the activity 

 remains the same as in normal animals, or in short pieces includ- 

 ing little besides the head-region, is apparently even greater than 

 normal. Consequently these pieces must require as much nutri- 

 tive material in proportion to their size as do normal animals, or 

 probably even more in the case of short pieces. Moreover, these 

 pieces undergo qualitatively complete form-regulation, producing 

 a new postpharyngeal and pharyngeal region with a new pharynx. 

 These changes must also require nutritive material. In such pieces 

 the intestinal contents decrease rapidly in amount — the shorter 

 the piece, the more rapid the decrease — and those portions of the 

 intestine remaining never contain any considerable amount of the 

 products of degeneration as do those of the shorter headless pieces. 

 These products appear to undergo resorption almost as rapidly as 

 thev are formed. Consequently the quantity of intestinal con- 

 tents becomes very small and the axial intestine and all other parts 

 become very slender (Compare for example Figs. 9 and 10 with 

 Figs. 15 and Figs. 18 and 19). As noted above this difference 

 indicates that the products of degeneration serve as nutritive mate- 

 rial. Since this does not accumulate to any extent in the pieces 

 with heads the intestine becomes almost empty and, notwithstand- 

 ing the normal movements of these pieces, the mechanical stimu- 

 lation oi the intestinal walls must be very slight and must decrease 

 centrifugally. Consequently the branches disappear and the 

 rapidity of degeneration is determined, at least in part, by the 



