454 'Journal of Comparative Neurology and Psychology. 



to YERKES,the medusae seldom swimming in a direction away from 

 the shadow. With these observations the work of the present writer 

 does not agree. He has failed to find that, in the case of the porce- 

 lain dish experiment, the vessel being illuminated by sunlight fall- 

 ing directly perpendicularly, the medusae swim oftener toward the 

 shadow than in any other direction. The medusae begin to swim 

 in all directions, many of them upward, some following the walls 

 of the vessel directly away from the shadow. Being thus in motion 

 almost incessantly, and swimming in all directions, it is obvious 

 that sooner or later they will enter the dark area. Once having 

 entered this area, the stimulating effect of sunlight being cut off, 

 they remain as in a trap. 



The application of the theory of trial and error which Jennings 

 ('06) has used so effectually for Protozoa and Rotifera, Mast ('03) 

 for Hydra, and Hargitt ('06) for tubicolous annelids, to the 

 present case is quite evident and requires no comment. Yerkes 

 has accounted for the reaction in the light of the theory of tropisms 

 of Verworn, J. LoEB, Holt and Lee, and others. He believes 

 that the sunlight striking one side the bell more directly, stimu- 

 lated this one side to contract in advance of the other, or more 

 strongly, the result being to turn the animal back into the shadow. 

 On this explanation it is difficult to see how, w^hen the medusae are 

 swimming, a beam of sunlight, falling perpendicularly, would cause 

 the medusae to swim into dark, as they do, as will be seen from 

 the accompanying table: 



Table Showing' the Movement of Gonionemus from the Sunlight into the Shadow. 



No. 



