360 L. MURBACH. 



light. Morse obtained his result with a limited number of rest- 

 ing or moving medusae. From the conditions of his experiment 

 we may infer that in some cases he did not get a response in less 

 than three minutes. In my own experiments I rejected any re- 

 actions that did not take place within a minute after the stimulus 

 was applied. As to the direction of turning into or away from sun- 

 light there is not so great uniformity. Had I taken a few cases 

 like the one of the relaxed medusa above, I would have gotten 

 high percentages. As it is, I have a large enough result (56 per 

 cent.) to conclude with others that Gonionemus turns away from 

 strong light. But on carefully observing this turning it is evident 

 that not in many cases do the medusae turn in such a way that 

 their continued swimming would take them parallel with the light 

 direction. Not infrequently they turn back into the strong light, 

 as has also been observed by others, 15 or are not turned far 

 enough. Is not Morse's ingenious explanation, given below, also 

 a tacit admission that the mere turning by strong light does not 

 cause a medusa to move parallel to the light direction? This 

 turning, therefore, cannot be considered true orientation, and 

 would not lead to swimming directly away from the source of 

 light. But since it has been shown to be a response to strong 

 light, the question remains as to its use to the. organism. In 

 nature the medusae are probably exposed to sunlight only when 

 they are disturbed and swim to the surface, or when the location 

 of one is exposed as the sun's rays come in a different direction. 

 If now the medusas were to be oriented and swim away from the 

 light it would take them downward, as Morse 16 has already 

 pointed out. It is to be noticed also that both in nature and in 

 aquaria, the bottom prevents this, and in a measure compels 

 swimming toward the region of lesser illumination if the turning 

 by light has been anywhere within half a sphere. It will be seen 

 that this behavior, repeated, even if no further directed move- 

 ment takes place, will be helpful in temporary escape from strong 

 sunlight. 



WAYS OF GETTING INTO OPTIMUM LIGHT. 

 If I have succeeded, so far, in making my position understood 

 the question will naturally arise, How do the medusae get into 



w jottr. of Comp. Neural. Psyehol., 1906, Vol. XVI., p. 455. 



