196 THE ELEMENTARY NERVOUS SYSTEM 



tentacles of the hydranth close and open at regular inter- 

 vals as they did in the normal feeding responses; the 

 rates of response in the two parts are, however, quite 

 different. Thus in a normal polyp whose feeding move- 

 ments had been carried out for some time at intervals of 

 2.5 to 3 minutes the hydranth and stalk were separated, 

 after which the stalk responded every 8 to 9 minutes and 

 the hydranth every 3.5 to 4 minutes. Thus each part in- 

 dividually had a slower rate than the whole animal, the 

 > stalk being much slower than the hydranth. It would be 

 natural to expect that one or other of these parts might 

 serve as a pacemaker for the whole system, but of this 

 there is no evidence. 



In a similar way a stalk may be cut crosswise in 

 halves and the two halves will continue to show rhythmic 

 contractions. As in the former case, both halves have a 

 slower rate than the whole stalk had. Possibly in both 

 cases the reduced rates give evidence of a general con- 

 trol which is somewhat disturbed by the cutting, though 

 of this there is no conclusive evidence. 



Besides the type of feeding that has just been con- 

 sidered and that is apparently characteristic of quiet 

 water, a second type is also to be noted (Torrey, 1904 &). 

 When detritus of one kind or another is carried by a 

 gentle current on to the expanded proximal tentacles of 

 an erect Corymorpha, these are very likely to wave in- 

 ward, carrying everything with them toward the distal 

 tentacles, which in turn move quickly outward to meet 

 the incoming proximal members and eventually trans- 

 port their booty to the mouth. In this way under favor- 

 able circumstances much food is doubtless obtained, but 

 the success of this operation is inn. \\ more dependent 

 upon accident and tin 1 whole procodnt seems to have less 



