Studies on Regulation. 475 



alic ganglia: in general the motor activity falls further and further 

 below the normal as the portion of the ganglia removed or injured 

 increases. It is often difficult with the present technique of 

 operation upon these forms to determine the extent of injury to 

 the small ganglia, but notwithstanding this difficulty my observa- 

 tions indicate very clearly that a relation exists between coordi- 

 nated motor activity and the amount of ganglionic tissue present. 

 When the cut passes through the middle of the ganglia both pieces 

 separated behave essentially like normal animals, but when less 

 than half of the ganglionic tissue remains intact the piece behaves 

 much like specimens without ganglia and if the portions of the 

 ganglia remaining are very small there is almost no motor activity 

 except the ciliary movement, unless the piece is strongly stimu- 

 lated. Since the ganglia are small and the difficulty of making a 

 section in them at exactly the level desired is great, and since it is 

 often difficult to determine after section just what parts of the 

 ganglia remain, the results of these experiments are not exact. 

 But the fact that the two pieces of an individual separated by a 

 cut through the middle of the ganglia both behave like normal 

 animals shows that the removal of half of the ganglionic tissue 

 does not affect the behavior appreciably. Moreover, it makes 

 no difference in such cases whether the cut is-longitudinal or other- 

 wise. Anterior and posterior halves and right and left halves of 

 the ganglia seem to be essentially alike in this respect. 



Pieces from the region anterior to the ganglia show almost no 

 motor activity except that of the cilia, which continue to beat, and 

 some degree of contraction after strong stimulation. Such pieces 

 die in the course of two or three days. 



These relations between the various regions of the nerve cords 

 and the cephalic ganglia and coordinated motor activity will be 

 illustrated in the consideration of individual cases. The fact of 

 the relation is of interest and indicates, in my opinion, that co- 

 ordination is connected in these forms rather with a certain extent 

 and structural complexity than with certain definite organs or 

 centers. Certainly the cephalic ganglia are more important for 

 motor activity and coordination than the other portions of the 

 nervous system, but it is possible that their connection with the 



