356 



L. MURBACH. 



before a window (cf. Fig. i). If the light is still stronger than 

 their normal they will continue in their attempt to get farther 

 away. When the aquarium is evenly lighted with subdued light 

 the medusae are evenly distributed and generally at rest. This 

 may be brought about by darkening the window, and the room 

 if necessary, until the light is uniformly weak. If, now, the side 



crq 



FIG. I. Top View. 



of the aquarium away from the window is darkened still more, 

 then the medusas are again set into activity, moving about until, 

 after some minutes, they will be found collected in the side of 

 the aquarium near the window. 3 In nature there is probably no 

 collecting in groups, as they are not confined. 



v DIRECTED MOVEMENTS. 



The main question in my mind has always been whether these 

 medusae are really directed by light, or properly oriented, even if 

 they could keep the course, /. e., continue oriented or directed. 

 My own experiments have led me to believe that the movements 

 of Gonionemus in response to light are not so definitely directed 

 by light as has heretofore been held, and that quantitative differ- 

 ences near their optimum constitute the natural light stimulus. 

 In regard to directed movement, Yerkes 4 says : " It is impossible 

 because of the form of the medusa and its mode of locomotion, 

 that the direction of its movements be as accurately determined by 

 light stimulation as are those of ... other animals whose structure 

 permits of more accurate orientation in reference to the source of 

 light." While no doubt in a measure true, to me it seems that 

 this statement is not wholly borne out by the fact that it can swim 



3 Because of the observation above I cannot agree witb Morse that Gonionemus 

 is not positively phototactic. 



4 Amer. Jour. Physio/., 1902, Vol. VI., p. 448. 



