202 G. H. PARKER 



especially if the region through which the puncture is made is 

 previously anesthetised with magnesium sulphate. I could not 

 see that the injected juice escaped from the mouths of the ani- 

 ! mals which, however, took in a considerable amount of sea- 

 water and enlarged much as well fed actinians do. After an 

 hour or so I tested the tentacles of the injected actinians with 

 fragments of mussel and found them very noticeably insensitive 

 to food. It therefore seemed clear that it was the food in the 

 gastrovascular cavity rather than any accidental overflow that 

 had influenced the tentacles. 



I have already pointed out reasons for believing that the 

 change in the responses of the tentacles after continuous feeding 



I is due to sensory fatigue and not to a general metabolic change 

 and I believe that the same is also true in the particular instance 

 under consideration. Though the meat juice injected into the 

 gastrovascular cavity unquestionably serves as material for 

 metabolism and eventually must have its influence on the ani- 

 mal's general state, its first condition is that of a component of 



X the fluid mixture which bathes the inner surfaces of the actinian. 

 ^ These surfaces include the cavities of the tentacles. As I have 

 'shown elsewhere (Parker, '17a) substances in solution in the 

 gastrovascular space of such organs as the large tentacles of 

 iCondylactis penetrate in a very short time the thin walls of 

 (these parts and thus make their way to the exterior. In doing 



v^so they must come in contact with the sensory ectoderm. Since 

 the changes in the reactions of the tentacles produced by food 

 juices injected into the gastrovascular cavity are in the direc- 

 tion of diminished response and since these changes come over 

 the tentacles with considerable rapidity and before a modified 

 metabolism dependent upon new food could have got much 

 headway, I believe that the loss of responsiveness in this instance, 

 like that in the former case, is due to sensory fatigue and not 



' changed metabolism. In the first instance the fatigue was pro- 

 duced by the direct application of stimulating substances to the 

 exterior of the tentacles; in the second to the transfusion of those 

 substances from the cavities of the tentacles to their sensory 

 mechanism. If this explanation is correct, as there is good reason 



