366 



L. MURBACH. 



hausted. The fact that inhibition and turning do not take place 

 under glass indicates that light does not cause either. The above 

 observations suggested to me that contact of the apex of the 

 bell with air may cause cessation of movement. This idea is 

 apparently supported by holding a layer of air imprisoned 

 under a petrie dish cover some distance below the surface of the 

 water. The animals respond the same as at the surface. 

 Nevertheless, longer observation of the behavior suggests that 

 it is after all, perhaps, nothing more than the recoil of a last 

 ineffective stroke ; something as when a person, finding one less 

 step than he expected at the top of a stairway, does not immedi- 

 ately contract his muscles for another step but loses his equi- 

 librium. Light not being the cause of the inversion (with 

 Morse 38 ), nor of inhibition, no further discussion is warranted 

 here. 



ARE THE MEDUS/E DIRECTED BY LIGHT RAYS? 

 Morse 39 has decided from an experiment with oblique illumina- 

 tion over the end of a shaded aquarium, because the medusas col- 

 lect in the ray-direction-end of the aquarium rather than in the 

 shaded end, that " the direction of the ray of light is the important 



re 

 CL 



C/q 



o 











FIG. 2. Top View. 



factor in orientation." Has he not left out of consideration another 

 important factor, that of light intensity in the aquarium ? Change 

 of intensity has already been shown to be the important stimulus 

 in reactions to light, nevertheless, it seemed worth while to test 

 whether it is ray direction or intensity that determines where the 



Jour. Comp. A T eurol. Psycho!., 1906, Vol. XVI., pp. 450, 451. 

 39 Amer. Nat., 1907, Vol. XLL, p. 684. 



