Yerkes, Behavior of Gonionemus. 459 



first of these apparently paradoxical statements made by me'is that, 

 the medusas under certain conditions at first gather in a region of 

 bright illumination and later come to rest in a shaded region. In 

 his experiments, Mr. Morse did not observe "a collection of the 

 medusae in the illuminated portion of the vessel."^ As I was 

 utterly unable to account for the disagreement in our results I at 

 once repeated my former experiments. Eleven medusae were 

 placed in a white earthenware dish such as Ayer and I used in our 

 experiments with Gonionemus. The dish was illuminated by 

 direct sunlight from a southeast window. All of the animals at 

 once began to swim about actively, mostly, however, keeping close 

 to the bottom of the dish as if seeking to move away from the light. 

 After a few seconds one-half of the dish was covered with a piece 

 of black cardboard. Within a minute, ten of the eleven medusae 

 were in the sunlit portion of the dish, and there they remained 

 for about two and a half minutes, swimming about actively but 

 without moving far in any direction. Then, as quickly as they 

 had gathered in the sunlit portion, they moved to the shaded 

 portion, and in less than a minute all but two were in the shade of 

 the cardboard. 



There is no doubt in my mind that the behavior just described is 

 due to a complex of stimuli and internal states of which light, 

 temperature and the condition of the organism are of prime impor- 

 tance. I have always suspected that the temporary gathering of 

 the medusae in bright light which I have repeatedly observed is due 

 rather to the strong stimulating power of the light than to any 

 definite directive influence. The matter deserves further attention, 

 for Ayer and I have done little more than call attention to the 

 fact. 



The second paradox appears in my statement that "when an 

 individual, in swimming about, chances to cross from the sunlit 

 region into the shadow, it very quickly ceases swimming and sinks 

 to the bottom. If, later, in swimming about it chances to cross 

 from the shaded region into the sunlight, it in most cases immedi- 

 ately ceases swimming, turns over, and sinks passively to the 

 bottom. "2 



Perhaps the contrast between "very quickly" and "immedi- 

 ately" in the above description was not sharp enough. At any 



^Journ. Comp. Neurol. Psychol., Vol. i6, p. 452. 1906. 

 ^Amer. Jour. Physiol., Vol. 9, p. 282. 1 903. 



