NERVOUS TRANSMISSION IN THE ACTINIANS 



91 



In all the experiments thus far described the responses of the 

 longitudinal mesenteric muscles followed quickly the applica- 

 tion of the stimuli, certainly in less than a second. There seems 

 therefore to be no doubt that the transmission is a true nervous 

 operation. Moreover, as the position of the application of the 

 stimuli and the direction of the cuts show, the pedal disc, the 

 column, and the oral disc must contain nervous connections of a 

 net-like character by which the ectodermic surfaces are put into 

 direct connection with the longitudinal mesenteric muscles. 

 There is further the strongest kind of physiological evidence for 

 nervous connections from the ectoderm directly through the 



Fig. 3 Side view of a Metridium on which an oblong outline has been cut 

 through the column wall (Experiment 10) ; A', region of stimulation. 



mesogloea to the entoderm. Of the regions thus far mentioned 

 the one in which these nervous connections are least developed 

 is the equator of the column. 



11. If a Metridium is cut vertically in two so that the result- 

 ant parts are connected only by the lips, not even the esophagus 

 or the oral disc remaining intact, and a mechanical stimulus is 

 applied to the column of one part, the portion of the oral disc 

 in that part regularly retracts, that in the other usually does not. 

 This form of experiment was repeated many times and with al- 

 most invariable results; it was onl}^ very rarely that the appli- 

 cation of a stimulus to the column of one side was followed by a 

 fesponse from the longitudinal muscles of the other side. It, 



