688 



THE AMERICAN NATURALIST [Vol. XLI 



highly reflectmg sides. Moreover, it is not clear from Yerkes' 

 text that light of the same intensity was used since some of his 

 experiments were conducted from 4 in the afternoon until 9 at 

 night; at such times the light would be constantly decreasing in 

 intensity. Again, he obtained the reaction by agitating the water, 

 setting the medusae swimming in all directions. Under such con- 

 ditions it would be very difficult to determine how much the move- 

 ments of the jelly-fish were due to its own activities and how much 

 to the currents set up by the agitation. 



The writer's experiment described above where light was thrown 

 on a swimming medusa shows too, that the reaction to light is the 



as Yerkes believes. Inasmuch as experiments conducted under 

 more normal and more carefully arranged conditions do not exhibit 

 the reaction, the writer believes that Gonionemus is at no time 

 positively phototactic. 



These experiments lead, moreover, to the conclusion that the 

 reaction of Gonionemus to light is a tropic one, and that the 

 accumulation of the animals in shaded areas is referable to the 

 method of "trial and error." 



The thanks of the writer are due to Dr. T. H. Morgan for many 

 suggestions in regard to the work and to the IMarine Biological 

 Laboratory for facilities. 



College of the City of New York 



