FOOD AND THE NERVE-NET 143 



vidual. This has been tested by cutting out the cesoph- 

 ageal tubes from several specimens of Metridium, laying 

 them open and experimenting with them as ciliated mem- 

 branes. If they are carefully prepared from animals that 

 have not been recently fed, they will show a well-marked 

 ciliary reversal to pieces of clean niter-paper. To frag- 

 ments of mussel they reverse the ciliary stroke in the 

 way characteristic 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. It is, there- 

 fore, believed that the general metabolism of Metridium 

 is not so much concerned with the change in the charac- 

 ter of the response of the cilia to filter-paper as the fa- 

 tiguing of the receptive mechanism of the ciliated surface 

 is. In the undisturbed state this mechanism is at its 

 greatest sensitiveness, but, on feeding, its efficiency dimin- 

 ishes and hence filter-paper no longer excites a reversal, 

 a change which is now called forth only by the more vig- 

 orous stimulation from the dissolved products of the food. 

 Hence the activities of the oral cilia are probably even 

 more independent of the rest of the actinian than Alla- 

 bach (1905) was inclined to insist upon. 



The feeding movements of the tentacles in actinians 

 are obvious neuromuscular reactions, as their disappear- 

 ance on narcotization with chloretone amply shows. The 

 independence of the individual tentacles in their feeding 

 reactions has been demonstrated in a number of forms, 

 in which these responses have been observed after the 

 tentacles have been cut from the polyp. That one ten- 

 tacle can influence another through connections in the 



