198 G. H. PARKER 



The occasion of this loss of the power to reverse the stroke of 

 the oral cilia on mechanical stimulation has been ascribed by 

 AUabach ('G5, p. 39) to the difference in metabolism between a 

 well fed and an underfed individual. I have tested this by 

 cutting out the esophageal tubes from several specimens of 

 Metridium, lajdng them open and experimenting with them as 

 ciliated membranes. If they are carefully prepared from ani- 

 mals that have not been recently fed, they will show a well 

 marked ciliary reversal to pieces of clean filter-paper. To frag- 

 ments of mussel they reverse the ciliary stroke in the way char- 

 acteristic for food and after a dozen or more such trials they 

 will no longer reverse to pieces of clean filter-paper. Thus the 

 isolated membrane exhibits all the changes that it does as a 

 part of the whole animal and under conditions where it is quite 

 obvious that the one change that it has suffered is fatigue. I 

 therefore believe that the general metabolism of Metridium is 

 not so much concerned with the change in the character of the 

 response of the cilia to filter-paper as the fatiguing of the recep- 

 tive mechanism of the ciliated surface is. In the undisturbed 

 state this mechanism is at its greatest sensitiveness but on feed- 

 ing its efficiency diminishes and hence filter-paper no longer 

 excites a reversal, a change which is now called forth only by 

 the more vigorous stimulation from the dissolved products of 

 the food. Hence in my opinion the activities of the oral cilia 

 are more independent of the rest of the actinian than even 

 Allabach ('05, p. 38) was inclined to insist upon. 



The feeding movements of the tentacles in actinians are obvi- 

 ous neuromuscular reactions, as their disappearance on narcoti- 

 zation with chloretone amply shows. The independence of the 

 individual tentacles in iheir feeding reactions has been demon- 

 strated in a number of forms, in which these responses have 

 been observed after the tentacles have been cut from the polyp. 

 That one tentacle can influence another through connections in 

 the oral disc has been proved for Condylactis and is probably 

 true for Metridium. The muscular responses of the tentacles 

 in feeding, therefore, give much more opportunity for unified 

 action than do the ciliary responses just considered. 



