144 THE ELEMENTARY NERVOUS SYSTEM 



oral disc has been proved for Condylactis and is prob- 

 ably true for Metridium. The muscular responses of the 

 tentacle in feeding, therefore, give much more opportu- 

 nity for unified action than do the ciliary responses just 

 considered. 



That tentacular responses in actinians change with 

 continued activity has long been recognized. Jennings 

 (1905) found that the tentacles of Stoichactis after they 

 had been vigorously plied for a while with meat ceased 

 for a time to react to food. Allabach (1905) noted that in 

 Metridium the tentacular reactions became gradually 

 slower or even ceased as feeding progressed, and the 

 same is recorded by Gee (1913) for Cribrina. Evidence 

 of this in Metridium was long ago published (Parker, 

 1896) and recent work on this point has been entirely 

 confirmatory. 



Jennings (1905) attempted to explain this change as 

 due to loss of hunger, 1 but Allabach (1905) showed that 

 it also occurred when the tentacles were stimulated, 

 though the animal was not allowed to swallow the food. 

 Her conclusion is that it is simply the effect of fatigue. 

 Gee (1913), however, declined to accept this explanation 

 because if an actinian that will ordinarily show this ten- 

 tacular change after having been fed eight or ten times, 

 is experimented upon when in a fresh condition and is 

 made to contract about the same number of times, its ten- 

 tacles are found not to have lost their responsiveness. 

 But both Allabach and Gee have failed to recognize that 

 ill ore are several kinds of fatigue. It is perfectly clear, 



1 It is perhaps unfortunate that the term hunger should have been used, 

 for it is somewhat ambiguous. Usually it stands for a well known sensa- 

 tion due to movements of the stomach (Cannon and Washburn, 1912) ; less 

 commonly for insufficient bodily nutrition. Pathology has long since demon- 

 strated that these two phenomena are not necessarily connected, but in 

 which sense Jennings intended to uo the term is not always wholly clear. 



