^ ■ 'u Yerkes, Behavior of Gonionemus. 463 



destroy one another. When Gonionemus in swimming from a 

 low intensity of Hght into a high intensity responds to the sudden 

 increase of light by turning over and sinking to the bottom, its 

 reactions conform to the local action tropism theory in that 

 stronger stimulation of the bell on one side than on the other, causes 

 that side to contract in such a manner as to turn the bell away from 

 the strongly stimulated side. If the organism happens to make a 

 complete circle because of the force of contraction of the stimu- 

 lated side of the bell, and this often occurs, it is brought into the 

 strong light again and the same reaction may be repeated, with 

 some variation perhaps. Unless this directive influence of the 

 unequal contraction soon brings the medusa into the weak light, 

 other forms of reaction inevitably appear, for the relation of the 

 animal to the stimulus has changed because of the continued action 

 of the light. Is this a series of trial and error reactions or is it 

 merely an instance of the complex relations of local action and the 

 various forms of reaction exhibited by Gonionemus } I should say 

 that it is trial and error only from a superficial view, for analysis of 

 the conditions of reaction indicates that local action determines 

 the direction of the medusa's movement in a pronounced way 

 when certain rather unusual conditions exist. Change the condi- 

 tions — even the repetition of a given photic stimulus may meet 

 with a form of reaction markedly diff'erent from the directed 

 movement due to the local action eff^ect of the original stimulus 

 because of the changes in the physiological condition of the organ- 

 ism — and a new form of reaction appears. 



At the earliest possible date I shall undertake a thorough study 

 of the light reactions of Gonionemus in their relations to other 

 external conditions, as well as to the physiological states of the 

 organism. 



Woods Hole, Mass. 

 September 20, 1906. 



