ROBERT M. YERKES. 



special significance in the life of the medusa. And in support of 

 this belief it is worth noting that they are almost always held dif- 

 ferently from the others. When the majority of the tentacles of a 

 "bell up" (exumbrellar surface uppermost) individual are resting 

 on the bottom of the vessel, the primary tentacles are usually held 

 slightly higher in the water than the others. They are used for 

 attachment and for food seizing sooner than the others. These 

 facts point toward either a specialization or a modification in func- 

 tion which is of interest because of its bearing upon certain 

 neuro-anatomical facts which have been presented by Miss Hyde. 1 

 She finds well-defined cell-fiber tracts along the radial canals. 

 This being the case we should expect the radial canal tentacles to 

 have a more important and direct influence upon the reactions of 

 the organism than have the other tentacles. 



When the medusa is stimulated to motion by light the tenta- 

 cles contract from . I .2 second before the bell. At times tentacle 

 reactions occur in the absence of a general bell contraction. 

 As determined with a stop-watch the reaction-time of the normal 



I. REACTION-TIME OF NORMAL TENTACLES TO DAYLIGHT. 



II. REACTION-TIME OF TENTACLES OF EXCISED MARGIN TO DAYLIGHT. 



II. REACTION-TIME OF EXCISED TENTACLES TO DAYLIGHT. (AVERAGE OF 



FIRST THREE REACTIONS.) 



1 Hyde, Ida H.: " The Nervous System of Gonionema Murbachii," BIOLOGICAL 

 BULLETIN, Vol. IV., 1902, pp. 40-45. 



