StuJuw on Regulation 379 



trequenr, hence the change in conditions in the region undergoing 

 regulation is less extreme than when the ganglia are present, and 

 degeneration is therefore somewhat less rapid than in pieces with 

 ganglia. As will appear below, however, this is true only for 

 headless prepharyngeal pieces of considerable length in which but 

 little of the anterior end posterior to the ganglia has been removed. 

 In short pieces neither a new postpharyngeal region nor a new 

 pharynx is formed and the intestinal changes are very different 

 from those described above. 



The development of new short and slender intestmal branches 

 in the postpharyngeal region after redifferentiation in the longer 

 pieces is in all probability also a response to a functional stimulus. 

 These branches correspond m arrangement and direction to the 

 branches in a normal postpharyngeal region (Fig. 9). Their 

 failure to appear in the shorter anterior prepharyngeal pieces is 

 undoubtedly due to the fact that in these pieces the intestinal con- 

 tents are used up more rapidly than in longer pieces, probably in 

 consequence of the extreme activity which is characteristic of the 

 short pieces: perhaps also the terminal region of the intestine con- 

 tains less reserve material than other parts. Thus the intestine 

 becomes almost completely empty and very thin-walled after about 

 two months in pieces including only the anterior fourth of the pre- 

 pharyngeal region, and the pieces die, while in pieces including the 

 anterior three-fourths of this region this condition is not reached 

 after about five months. Thus in the short pieces there is proba- 

 bly neither sufficient nutritive material available nor sufficient 

 intestinal contents to furnish a stimulus to the formation of new 

 intestinal branches in the redifferentiated postpharyngeal region. 



It is of interest also to note that when new intestinal branches 

 appear in the redifferentiated region they never develop to larger 

 size than the intestinal branches of other regions which are under- 

 going reduction. It seems difficult to account for this early ces- 

 sation of development on any other than a functional basis, but 

 according to this hypothesis it is difficult to see why development 

 should proceed farther, for the functional conditions connected 

 with the presence of fluid contents are similar, quantitatively, in 

 this region as elsewhere. 



