L. MURBACH. 



ence from his original experiment was correct for all medusae 

 falling on the border between sunlight and shade so that " part 

 of the body is in the shadow." 



DOES LIGHT ORIENT Gonionemus? 



Although Gonionemus does not move parallel to the direction 

 of stronger light it has been held that its 'movements are directed 

 by stronger light and that it thus gets from an unfavorable to a 

 favorable light place by direct responses or movements suited to 

 this purpose. Yerkes says : n " This is apparently accomplished 

 by the more forceful and earlier contraction of that side of the 

 bell farthest away from the shadow.'' In the case of other 

 stimuli (tactual and electrical) he had demonstrated this but not 

 in the case of light. Though, page 285, we read: "Observa- 

 tion indicates that the side of the organism which is exposed to 

 the most intense light contracts first and most strongly thus 

 forcing the bell over," yet there is scarcely the weight of proof 

 in this observation. In a later paper Yerkes 12 says: "... 

 brilliant illumination of one side of the bell . . . brings about 

 movement toward the region of lower illumination." This is 

 based on an experiment of throwing sunlight on part of a 

 medusa. He gives 66 per cent, as turning toward the region 

 of lower illumination. 



Morse 13 restates the same explanation of the turning mechanism, 

 and from the experiment of mutilating one side of the medusa 

 shows that by the resulting one-sided contraction circle swim- 

 ming is induced. In a later publication 14 he has shown that 

 light has the same effect, i. e., to turn the animal. Half of a 

 medusa in the dark was illuminated by a vertical beam of light. 

 This caused "... the medusa to swim vertically upward, and 

 it was only after it had pulsated three or four times that its path 

 veered from the perpendicular. The result of one hundred trials, 



only sunlight falling perpendicularly, and in another experiment in which he used 

 oblique light it had no reference to Yerkes's former experiment. More medusae would 

 fall in oblique light with bodies partly in the shadow than in vertical. 



n Airier. Jour. Physio/., 1903, Vol. IX., p. 284. 



I2 jaur. of Comp. Neurol. Psycho!., 1906, Vol. XVI., p. 461. 



I3 jour. of Comp. Xeurol. Psycho/., 1906, Vol. XVI., p. 451. 



u Amer. Nat., 1907, Vol. XLI., p. 683. 



