ACTINIAN BEHAVIOR 199 



That tentacular responses in actinians change with continued 

 activity has long been recognized. Jennings ('05, p. 400) 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 ('05, p. 38) noted that in Metridium the tentacular 

 reactions became gradually slower or even ceased as feeding 

 progressed, and the same is recorded by Gee ('13, p. 320) for 

 Cribrina. I long ago published evidence of this in Metridium 

 and my recent work on this point is entirely confirmatory. 



Jennings ('05) attempted to explain this change as due to loss 

 of hunger,' but (Allabach, '05) showed that it also occurred when 

 the tentacles were stimulated but the animal was not allowed 

 to swallow the food. Her conclusion is that it is simply the 

 effect of fatigue. Gee ('13, p. 324), however, declined to accept 

 this explanation because if an actinian that will ordinarily show 

 this tentacular 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 tentacles are 

 found not to have lost their responsiveness. But both Allabach 

 and Gee have failed to recognize that there are several kinds of 

 fatigue. It is perfectly clear, from Gee's experiment, that mus- 

 cular fatigue is not accountable for the change in the responsive- 

 ness of the tentacles, but it is entirely possible that it may have 

 been caused by sensory fatigue. It is a common observation 

 that if a sensory surface is placed under active stimulation, it 

 is often only a short time before it will fall off very considerably 

 in its receptiveness and it is this form of fatigue, I believe, that 

 is accountable for the change in the tentacular responses of 

 Metridium on continuous feeding. I have had occasion several 

 times to repeat AUabach's experiment of placing food on the 

 tentacles of Metridium and, after they have responded, of remov- i 

 ing it from the lips before it was swallowed, and in all instances 



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 sensation due to 

 movements of the stomach (Cannon and Washburn, '12); less commonly for in- 

 suflacient bodily nutrition. Pathology has long since demonstrated that these 

 two phenomena are not necessarily connected, but in which sense Jennings in- 

 tended to use the term is not always wholly clear. 



