CONTBTBUTIONS FROM THE ZOOLOGICAL LABORATORY OF THE MUSEUM OP COMPARATIVE ZOOLOQT AT 



HARVARD COLLf:GE. NO. 284. 



NERVOUS TRANSMISSION IN THE ACTINIANS 



G. H. PARKER 



THREE FIGURES 



Experimental studies of the direction of nervous transmission 

 in the discs of medusae have been made by many investigators 

 since the days of Eimer ('78) and Romanes ('85), but very little 

 work of this kind has been done on polyps. The following ob- 

 servations were made on medium-sized specimens of Metridium 

 marginatum Milne-Edwards with the view of ascertaining some- 

 thing of the course of transmission in these animals. 



Perhaps the most usual response that Metridium and other like 

 actinians show is the retraction of the oral disc, and this response 

 has been made the chief basis of the following research. It can 

 be called forth easily by mechanical stimulation and it serves as 

 a reasonably good test for the sensitiveness of different parts of 

 the actinian's body to this form of stimulus. An exploration of 

 the surface of Metridium by means of a delicate, blunt glass rod 

 showed degrees of sensitiveness in various regions as follows : 



A. Almost insensitive to contact with the rod were the general 

 surface of the pedal disc, the lips, and the esophagus. 



B. Only very slightly sensitive were the column between the 

 oral disc and the sphincter, the intermediate zone of the oral 

 disc (the space between the tentacles and the lips), and the sur- 

 face of the siphonoglyph. 



C. Slightly sensitive were the tentacles and the equatorial 

 portion of the column. 



D. Fairly sensitive was the surface of the column in the neigh- 

 borhood of the sphincter. 



E. Most sensitive was the surface of the column near its 

 pedal margin, a fact already pointed out for other species by 

 Fleure and Walton ('07, p. 213). 



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