REACTION-TIME OF GONIONEMUS MURBACHII. 9! 



tentacle to the increase in light intensity caused by suddenly 

 uncovering a dish containing the medusa is from two to five 

 seconds. Reaction-time averages for three conditions of the 

 tentacle are given in table on page 90. 



A fact significant in this connection is that the excised tentacle 

 rapidly loses its power to react to photic stimuli. To the first 

 four or five repetitions of a stimulus it usually reacts quickly, 

 then the time of reaction, as is shown in the series herewith pre- 

 sented, rapidly increases until reaction fails entirely. 



SERIES OF REACTIONS OF AN EXCISED TENTACLE TO DAYLIGHT. 



Reaction I 4.6 



2 2.5 



3 8.7 



4 15-6 



5 35-o 



6 No reaction except to 



7 , mechanical stimulation. 



The reaction-time of the normal tentacle, 3.1 seconds, is con- 

 siderably shorter, as would be expected, than that of the bell. 

 Its variability is low. The reactions of the tentacles of excised 

 margins are slightly quicker, 2.4, according to the results pre- 

 sented, than are those of the normal animal, but they are also 

 more variable. The quickness of these reactions may possibly be 

 due to a temporary increase in the irritability of the margin caused 

 by the operation. Finally, the reactions of excised tentacles 

 are much longer, 4.5, and more variable than are those of either 

 the normal animal or the excised margin. This may mean that 

 the tentacle contraction in response to light is. normally initiated 

 by stimulation of the margin, or that the ability of the organ to 

 react is lessened by its separation from the bell. At any rate there 

 is a marked difference here indicated in the time of reaction of 

 isolated and normally attached organs, a difference which may 

 possibly be an indication of a function of the central nervous 

 system or of the special organs of light stimulation which are in 

 all probability situated in the margin of the bell. 



RELATION OF QUALITY OF STIMULUS TO TIME OF REACTION. 



The motor reaction of Gonionemus to increase in light is much 



slower than that to other forms of stimuli. This is due in part 



