THE RATE OF TRANSMISSION IN THE NERVE NET OF 

 THE COELENTERATES. 



By G. H. PARKER. 



(Contributions from the Zoological Laboratory of the Museum of Comparative 

 Zoology, Harvard College, Cambridge, No. 313.) 



(Received for publication, September 2, 1918.) 



Direct measurements of the rate of transmission in the nerve net 

 of the coelenterates seem never to have been undertaken heretofore. 

 Romanes (1878) and Harvey (1912) have both recorded the rate of 

 the contraction wave in medusae and, while it is probable that this 

 wave, as it can be seen coursing around the jellyfish bell, represents 

 the rate of nervous transmission, this method of determining such a 

 rate is at best indirect. In sea anemones the nervous and muscular 

 elements for some of their more striking responses are so much more 

 separated anatomically than they are in the jellyfishes that an inde- 

 pendent determination of the rate of nervous transmission is possible. 

 This is particularly true of Metridium marginatum, whose large size 

 permits the preparation of considerable lengths of tissue through which 

 transmission may be accomplished. 



It is well known that when the pedal edge of the column of Metrid- 

 ium is stimulated, the animal quickly responds by a vigorous con- 

 traction of the longitudinal mesenteric muscles, by which the oral 

 disc is retracted. This response occurs without the appearance of 

 muscular activity in the region intervening between the point of 

 stimulation and the responding muscles, and hence this region must be 

 assumed to be bridged over through the activity of nervous tissue. 

 Moreover, the pedal edge of the column of Metridium may be partly 

 cut off as a long tongue of tissue, one end of which can be left still 

 attached to the animal (Fig. 1). When the free end of this tongue, 

 which may be 10 to 15 cm. in length, is stimulated, the animal re- 

 sponds in the characteristic way but without exhibiting muscular 

 contraction on the length of the tongue itself. This portion of the 



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