LIGHT REACTIONS OF THE MEDUSA GOXIONEMUS. 359 



upon different individuals in the main " gave 70 per cent, in 

 favor of the view "that light has a directly orienting effect." In 

 considering this experiment we should know how many different 

 individuals were used, and should bear in mind that the time 

 limit for response was from five seconds to three minutes, and 

 that the turning began to show only after several pulsations. 

 This would seem to be different from Yerkes's view which is 

 that the medusae turn directly on stimulation by strong light. 



As my experiments were made before the above results were 

 published, and they favor the view of Yerkes that strong light 

 turns the animal immediately they may be added here. The 

 first test was made by using a horizontal band of sunlight as 

 wide as the aquarium, i cm. deep, and a little distance- -5 cm. 

 from the bottom. Darkening the aquarium momentarily was 

 the means of starting the medusae swimming up toward the band 

 of light. Usually five or more medusas were used to begin the 

 experiment. Forty-three per cent, were turned back by the band 

 of light, away from the source ; 33 per cent, turned toward the 

 source ; and 24 per cent, swam straight through the band of 

 sunlight. 1 ' 5 Now it was thought that an oblique band of sun- 

 light (similar to Fig. 3) would be more decisive, as one side of 

 the up-swimming,. medusa would be stimulated, not only more 

 strongly, but in ^divaiwe !pf>,the other. In this case 50 per cent, 

 of the medusae turned away from the direction of the sunlight 

 and 41 per cent, toward it ; 9 per cent, did not respond. A re- 

 laxed medusa, allowed to float bell downward, showed a more 

 striking result on touching the oblique band of sunlight. It 

 turned, and after swimming upward a few strokes, floated down, 

 only to do the same on striking the band ; the next time it floated 

 through and on emerging below turned in the opposite direction, 

 again away from the band of sunlight, but it continued in a circle 

 which again carried it up through the sunlight. 



There is enough difference in methods employed in our ex- 

 periments to leave no doubt that the medusae do turn at a sudden 

 transition into strong light, especially when they are in very weak 



15 I am compelled to agree with Morse that the collecting of this medusa in strong 

 sunlight is not a normal reaction, but rather due to previous excessive stimulation of 

 some kind. 



