86 



ROBERT M. YERKES. 



a rapid lengthening of the time of reaction. Thus : first reaction, 

 .506 sec. ; second, 1.003 ; third, 3.607. 



As compared with the reactions of the small medusa Gonione- 

 j/n/s, those of the jelly-fish Cyanca arctica are slow. Some indi- 

 vidual reaction-times of a single individual (Cyaned) to a four-cell 

 current, with electrodes in contact with opposite points on the 

 margin follow. 



Mean. 



1.530 Mean variation. .248 



Relative Variability 16.2. 



REACTION-TIME TO PHOTIC STIMULI. 



The reaction-time of Gonionemus to increase in light intensity, 

 as I have stated in another paper, 1 varies with the strength of the 

 stimulus, temperature, condition of the organism, etc., from one 

 to thirty seconds. To daylight the organism usually responds in 

 about seven seconds ; to sunlight the reaction is at first much 

 quicker, but it rapidly lengthens as the organism is exposed to 

 the influence of the intense light. The relation of time of reac- 

 tion to intensity is indicated by the following averages : Weak 

 daylight, 9.4 sec. ; daylight, 7.0 sec. ; sunlight, 5.5 sec. 



Moreover, the reaction-time varies with the size, sex, and pig- 

 mentation of the individual, as well as with such external condi- 

 tions as temperature, density, and chemical constitution of the 

 medium. Increase in temperature gradually shortens the time 

 from about 8-9 sec. at 19 C., to 2-3 sec. at 32 C. Decrease 

 in temperature lengthens the time, until reactions fail entirely at 

 about 10-12 C. 



1 Yerkes, Robert M., with the assistance of James B. Ayer, jr.: "A Study of the 

 Reactions and Reaction-Time of the Medusa Gonionema miirbackii to Photic 

 stimuli." Amer.Journ. Physiol., Vol. 9, 1903, pp. 279-307. 



