MICHIGAN ACADEMY OF SCIENCE. 



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large mirror (M. Fig. 2) was placed vertically against one corner of the 

 aciuarium 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 

 op])osite 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 15 minutes. Many of the medusae were scattered about, 

 Ixit again there was a larger number collected in the corner farthest from 

 the sources of light. In two other experiments a sort of spotlight effect 

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