REACTfON-TIME OF GONIONEMUS MURBACHII. 



Between these reaction-times of the Coelenterata and those of 

 most vertebrates, as well as of many invertebrates, there is a strik- 

 ing difference in rapidity. Whereas, the jelty-fish and medusa re- 

 spond to an electric stimulus in from one to four seconds, the fish 

 or frog responds in a fraction of a second, usually not more than 

 one fourth, and sometimes one tenth. Observe the reaction of 

 the fiddler crab to a shadow, and note how quick it is in com- 

 parison with the reaction of Gonionemus to the same change in 

 illumination. Is this difference in reaction-time due to a differ- 

 ence in sensitiveness (/. r., is the latency period of stimulation 

 longer) ; is there a difference in the rate of impulse transmission, 

 of central nerve processes, or of muscle contraction ? Such ques- 

 tions should be answered by means of reaction-time investigations. 

 The rate of impulse transmission (presumably nerve transmission) 

 is much slower in the medusa Gonionevnis than in the vertebrates 

 and most invertebrates thus far studied. Furthermore, it differs 

 for different regions of the medusa ; the margin and the radial 



canal regions transmit impulses much more rapidly than do the 

 inter-radial regions. The exumbrellar layer of tissue, so far as 

 I have been able to determine, does not transmit impulses at all. * 

 The frog reacts to such an electric stimulus as was applied to 

 Gonionevius in . i 50 .200 sec. In comparison the medusa's reac- 

 tion-time is very long ; but it differs in yet another respect it 

 is far more variable. The reaction -times and variabilities of the 

 reactions of frogs to three intensities of electric stimulation as 

 determined in an experimental investigation - are here given for 

 comparison with the results given by Goiiioncinus to three inten- 

 sities of light. 



1 Yerkes, Robert M. : "A Contribution to the Physiology of the Nervous System of 

 the Medusa Gonionema Murbachii. Part II. The Physiology of the Central Nervous 

 System,' 'Amer. Jour. Physiol., Vol. 7, 1902, p. 193. 



2 Harvard Psychological Studies, Vol. I., 1903, pp. 616-618. 



