460 ^Journal of Comparative Neurology and Psychology. 



rate, Mr. Morse noted no definite reaction as the medusa passed 

 from light to shadow, but instead merely a gradual cessation of 

 activity due, as he believes, to the absence of stimulation. 



I am compelled to disagree with the view that decrease in the 

 intensity of light means absence of stimulation. I have already 

 shown that a rather sudden increase in the intensity of light inhibits 

 the movement of an active Gonionemus, in most cases, whereas a 

 considerable decrease causes a more gradual cessation of activity, 

 and I have abundant evidence that change in the intensity of 

 light stimulates the medusa. Whether this change be increase or 

 decrease in intensity, it may either augment or inhibit the activity 

 of a moving individual and it may or it may not bring a resting 

 individual into movement. 



According to Mr. Morse, the third paradoxical statement in my 

 papers is that "the reaction to sunlight is a direct response whereby 

 the medusa turns directly toward the shadow and swims into it. "^ 

 I have never made any such statement, I believe, and I agree with 

 Mr. Morse that it is false. What I have said is, not that the 

 medusa swims toward the shadow, but instead that, "when it 

 chances to cross from the shaded region into the sunlight, it in 

 most cases immediately ceases swimming, turns over and sinks 

 passively to the bottom. But in this case when it again becomes 

 active, it does not move indifferently in any direction as it does 

 when in the shadow; instead it usually turns in such a way as to 

 move back into the shaded region."^ This is precisely what I said 

 and what I meant; I repeat the statement in the light of further 

 observations made during September, 1906. 



Mr. Morse's criticisms have served the good purpose of reveal- 

 ing to me an important omission in the description of the condi- 

 tions under which Mr. Ayer and I observed the behavior 

 described below. We omitted to state that the direct sunlight by 

 which the earthenware dish was illuminated came from a south- 

 east window and was not exactly perpendicular to the surface of the 

 water and the bottom of the dish. From our description, one is 

 led to infer that the line between light and shadow was perpen- 

 dicular to the bottom of the dish, whereas it inclined slightly 

 toward the shaded region. In the figure given in our paper^ to 



^Jour. Comp. Neurol. Psychol., Vol. l6, P. 45^- 1906. 



^Amer. Jour. Physiol., Vol. 9, p. 282. 1903. 



'Ibid. 



