146 THE ELEMENTARY NERVOUS SYSTEM 



condition in Cribrina. From these observations it seems 

 clear that changes induced in the muscular responses of 

 the tentacles of one side influence to no small degree the 

 reactions of the tentacles on the other side. As Jennings 

 (1905) has put it, the animal reacts as a unit, one side 

 influencing the other. Experiments of this kind have 

 been repeated on Metridium, and though the results were 

 not so striking as those described by the authors already 

 quoted, it was clear that when a Metridium was fed per- 

 sistently by means of the tentacles of one side and so as 

 to avoid touching with the food those of the other side, 

 the opposite tentacles w^ere nevertheless eventually in- 

 fluenced in their reactiveness and became less responsive 

 as the feeding proceeded. Here would seem to be a good 

 instance of some such general effect as that of changed 

 metabolism or the general utilization even of nervous 

 experience. 



To ascertain whether changes in the tentacular re- 

 sponses of one side of the disc are transmitted nervously 

 to the other side, small pieces of mussel were fed to the 

 tentacles of one side of a Metridium but removed before 

 they were swallowed and then, after the tentacles of that 

 side began to lose in responsiveness, those of the other 

 side were tested to see if they too had lost in their ca- 

 pacity to respond. The time in seconds required for the 

 swallowing of each piece of food is recorded in the fol- 

 lowing table. The rejection of a piece of food is indicated 

 by the sign of infinity. 



It must be evident from an inspection of Table 3 that 

 the right side of the animal gave no evidence of having 

 been influenced by the left and that therefore there is no 

 ground for the assumption that the experience of one side 

 is transmitted nervously to the other. In other experi- 



