128 



ELEVENTH REPORT. 



It 0^. 6 



factor in orientation." Has he not left out of consideration a very important 

 factor, that of light intensity? Change of intensity has already been shown 

 to be the important stimulus in the ordinary reactions to light. To test 

 whether it was ray direction or intensity that determines where the medusae 

 will collect the following experiments were tried: The aquarium used in 

 jjrevious experiments was ])laced before an open west window at 3 p. m. in 

 good dilTused daylight. Fig. 1. In 15 minutes the majority of the medusae 

 had retreated to the end of the aciuarium away from the window. Now a 



