LIGHT REACTIONS OF THE MEDUSA GON1ONEMUS. 



367 



medusas will collect. The following experiments were tried : 

 The aquarium used in previous experiments was placed before an 

 open west window at three o'clock in the afternoon, in good dif- 

 fused daylight. In fifteen minutes the majority of the medusae had 

 retreated to the end of the aquarium away from the window (Fig. 

 r > P- 356). Now a large mirror (M, Fig. 2) was placed vertically 

 against one corner of the aquarium away from the window, so as 

 to throw light across the end of the aquarium. In fifteen minutes 

 most of the medusae had collected in the opposite corner of the 

 aquarium away from the window and where the light was least 

 intense. The mirror was now placed at this corner and record 

 again made in fifteen minutes. Many of the medusae were scat- 

 tered about, but again there was a larger number collected in the 



FIG. 3. 



FIG. 4. 



corner farthest from the sources of light. In two other experi- 

 ments a sort of spot-light effect was produced, by having the 

 aquarium darkened except at one end, and a vertical strip 

 (Fig. 3) at one side next the open end so as to throw sunlight 

 across the open end diagonally. There was also a slit near the 

 top of the closed end of the aquarium for a band of sunlight or a 

 mirror beam. The medusae gathered farthest from the source of 

 light when sunlight was passed through the end of the aquarium. 

 Now crossing this sunlight by a beam from a small mirror, 

 through the slit, made the medusae leave the place where the 

 light overlapped- -where it was more intense. The position of 

 the sunbeam and mirror was reversed with a corresponding re- 

 sult. In this case the mirror was held high enough so that its 

 circumscribed area of reflected light fell on the farther corner of 



