312 G. H. PABKER 



one to expect that the longitudinal muscle would be more fully 

 developed on the oral than on the aboral side of the tentacle, 

 but of this I have been unable to find any evidence in sections 

 of these tentacles. 



The distal tentacles, which are much more restlessly active 

 than the proximal ones (Torrey, '04 a, p. 397), in moments of 

 rest form a cluster more or less surrounding the mouth. On 

 stimulation they quickly jerk backward away from the mouth 

 (Torrey, '04 a, p. 400) and point their tips toward the aboral 

 portion of the hydranth, after which they more slowly return 

 to their original position. On applying an anesthetic, mag- 

 nesium sulphate or chloretone, to a whole hydranth or to a 

 single isolated distal tentacle, all these reactions disappear in 

 from one to three minutes, to reappear after the material has 

 been for about two minutes in pure sea-water. It, therefore, 

 seems probable that in the case of the distal tentacles the reac- 

 tions are dependent upon the same interplay of parts as in the 

 proximal ones except that the longitudinal muscles of the dis- 

 tal 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 medusae them- 

 selves. The peduncles contract on stimulation and the medusae 

 are more or less rhythmically contractile. Both cease this 

 activity when they are anesthetized with magnesium sulphate 

 or chloretone, and both quickly recover from this condition on 

 being placed in pure sea-water. Hence their muscles are pre- 

 sumably under nervous control. 



Of the six sets of muscles in Corymorpha the two entodermic 

 muscles, the circular muscle of the stalk and the circular muscle 

 of the proboscis, are both slow in action 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 '10) 

 and in certain regions in actinians (Parker, '16). Possibly the 

 circular muscle of the proboscis is at times somewhat under 

 nervous control as, for instance, when that organ exhibits peri- 



