184 THE ELEMENTAEY NERVOUS SYSTEM 



appear after the material has been for about two minutes 

 in pure seawater. It, therefore, seems probable that in 

 the case of the distal tentacles the reactions are depen- 

 dent upon the same interplay of parts as in the proximal 

 ones, except that the longitudinal muscles of the distal 

 tentacles are probably more fully developed on their 

 aboral than on their oral faces. 



No attempt was made to work on the muscles of the 

 peduncles of the medusae or on those of the medusse them- 

 selves. The peduncles contract on stimulation and the 

 medusaB are more or less rhythmically contractile. Both 

 cease this activity when they are anesthetized with mag- 

 nesium sulphate or chloretone, and both quickly recover 

 from this condition on being placed in pure seawater. 

 Hence their muscles are presumably under nervous 

 control. 



Of the six sets of muscles in Corymorplia, the two 

 entodermic muscles, the circular muscle of the stalk, and 

 the circular muscle of the proboscis are both slow in ac- 

 tion and uninfluenced by such anesthetics as magnesium 

 sulphate and chloretone. They are, therefore, probably 

 directly stimulated and represent a primitive type of 

 muscle such as is found in sponges (Parker, 1910 a) and 

 in certain regions in actinians (Parker, 1916 a). Pos- 

 sibly the circular muscle of the proboscis is under certain 

 circumstances somewhat under nervous control as, for 

 instance, when that organ exhibits peristalsis, but or- 

 dinarily this muscle, like that of the stalk, probably re- 

 sponds only to direct stimulation. 



The four ectodermic muscles, the longitudinal muscles 

 of the stalk, of the proboscis, and of the two sets of ten- 

 tacles, are relatively quick in action and cease to respond 

 under the influence of anesthetics. These are probably 



