StitJirs oil Regulation 36 1 



l^Lir it is in connection with experiments on form-regulation 

 that the extreme plasticity of the turbellarian intestine becomes 

 evident. The changes in form and arrangement of the intestinal 

 branches in the experiments of Lillie ('01) and Bardeen ('01, '02, 

 '03) are sufficient to illustrate this point, although they do not 

 demonstrate its correlation with the functional conditions result- 

 ing from the movements and pressures ot fluid contents. 



In most triclads and polyclads intestinal regeneration is usually 

 much less complete than the regeneration of other parts when the 

 animals are not fed. Moreover, and this seems to me to be a 

 crucial point, it is much less complete in pieces without the ceph- 

 alic ganglia than m pieces contammg the ganglia (Child '04a). 

 It can scarcely be supposed that there is any essential difference in 

 nutritive conditions between pieces with and those without the 

 ganglia. If anything, more nutritive material should be avail- 

 able for growth in the piece without ganglia since it is much less 

 active than the other. I do not believe, however, that such differ- 

 ences in intestinal regulation can be due primarily to the differ- 

 ences in nutritive conditions. The only reasonable basis for 

 interpretation seems to me to lie in the differences in activity. 

 In the piece without ganglia the movements of the intestinal con- 

 tents are less frequent and less energetic, and consequently the 

 stimulus to intestinal growth in the new tissue is less than in the 

 piece containing the ganglia. Observation of two such pieces and 

 of the movements of intestinal contents in their bodies shows very 

 clearly that the intestinal pressures and tensions are much greater 

 in the piece containing the ganglia than in that without them. 



All the data thus far available seem to me to indicate that the 

 form and arrangement of parts of the turbellarian intestine is 

 determined very largely by mechanical factors due to the presence 

 and movements within it of fluid contents. This statement is not 

 to be interpreted, however, as signifying that nutritive factors plav 

 no part in determining intestinal form. The form must be altered 

 to a certain extent by the presence or absence of reserve material 

 in the cells, by the general metabolic conditions, the relation 

 between intake and output, etc. But I find it difficult to under- 

 stand how such factors as these can possibly determine the general 



